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r

Section and, Rounthwaite^s Pocket Book.

PATENT ASH DISCHARCIMC*"'^'*""'

SEE'S Patent Hydro- Pneumatic ASH EJECTOR

DIRECT-ACTING ASH HOIST , SELF-TIPPING ASH BUCKETS

No Noise. No Dirt.

No Waste of Steam.

Adopted by all the leading SteamBhlp Owners of the World. Fitted on every type of Steamer, including Passenger and Cargo Steamers, Warships, Yachts, Tugs, Trawlers, &c., <&a

GREAT SAVING OF LABOUR.

Ashes mixed with Sea-water discharged well clear of Ship's side.

Sole Proprietors and Patentees—

F. J. TR

Naval Arch 43 Bllllte

Telegraphic Address **

OR, L™

neers,

Section and RounthwaUe^s Pocket Bock.

I

THE YOBKSHIBE COPPEB WORKS, LIMITED,

LEEDS.

CONTRACTORS TO THE ADMIRALTY AND ALL GOVERNMENT DEPARTMENTS

SOLID DRAWN

TUBES

COPPER & BBASS

LONDON ^ ^

" 30 Gt. St Helen's, E^C 3

LIVERPOOL

" Royal Liver Building

GLASGOW ' '

" 78 McAlpine Street

NEWCASTLE ^

" Milburn House

CARDIFF ' '

" Asbestos House, Harrowby St,

''BEMAL" Brass Condenser Tubes

"LEESPEC

Copper Boiler Tubes

(Registered Trade Names)

Seaton and SourUkwaiie'a Pocket Booh.

COCHRAN

DONKEY

BOILERS

COAL OR OIL PIRBD FOR BTMM OP MOTOR SHIM ■UILT IN 32 BIZEB UP TO

1000 8q. Pt. HUTINO lURFME

WRITK POR OATALOQUE

^k

urn

^

SEATON & ROUNTHWAITE'S

MARINE ENGINEERING POCKET-BOOK

ENGINEERING

^n illiuitrateir Witthin lotrmal

PRIOE 1/-; post ftBOf 1/2^

FOR THE ENOINEERINQ TRADE AND PROFESSION AT HOME AND ABROAD

THE LEADING TECHNICAL JOURNAL

AND THE

BEST MEDIUM FOR ADVERTISEMENTS

A copy of our Directory of Current Adver- tisements (first issued in 1885), together with our Scale of Charges, will be sent post free on application. Over 100,000 are dis- tributed of each edition throughout the world to buyers of machinery.

SOLE ADDRESS —

35-36 BEDFORD STREET, STRAND,

LONDON, W.C.2

A POCKET-BOOK OF

MARINE ENGINEERING

RULES AND TABLES.

FOR THE USE OP

MARINE ENGINEERS, NAVAL ARCHITECTS,

DESIGNERS, DRAUGHTSMEN,

SUPERINTENDENTS,

AND ALL ENGAGED IN THE DESIGN, CON€TRUCTION, AND CARE OF

MARINE MACHINERY, NAVAL & MERCANTILE

BY

A. E. §EATON,

M.lNST.C.E., M.Inst.Mech.E., Vice-President, Inst N.A.,

M.Inst.MarineE., and Mem Cncl. Inst. Metals, &c. ;

AND

H. M. ROUNTHWAITE, M.Inst.Mech.E., M.Inst.N.A.

Fifteenth Edition, Revised.

WITH DIAGRAMS.

LONDON:

CHARLES GRIFFIN & COMPANY, LIMITED.

NEW YORK: D. VAN NOSTRAND CO.

1922. \^All Rights Reserved.]

31 91 82 jun 22 mi ttf

PREFACE TO FIRST EDITION. ;|^^

-»♦■

QuuiG

A special Pocket-book of Memoranda, Tables, &c., has long been a desideratum with Marine Engineers. In the existing pocket- books, Marine Engineering matters are only dealt with generally, and such information as is given is in some cases very restricted, in others obsolete, and in all too scattered to be useful. We, ourselves, have experienced this want, and have heard on all hands the desire expressed for a Pocket-book in which Marine Engineering questions are dealt with thoroughly, are easy to find, and not "mixed up" with general information in such a way as to render the seeking of them difficult and tedious.

We therefore trust that in presenting this book to the public we have not only fulfilled the task we set ourselves, but have supplied this long-felt want in a manner that will prove satis- factory to all engaged in Marine Engineering affairs. While we have been careful to make the book of special value to Marine ^ Engineers, we have omitted nothing, so far as we know, that is^ would be of use and importance to others having to do with Ships •* and their machinery ; at the same time, we nave avoided tne ^ introduction of extraneous matter of only general interest, which * would make the volume so bulky, and the arrangement of it so complex, as to very materially detract from its usefulness. Hence, we nave, while not altogether neglecting past experience, but omitting information now almost only historic, devoted our attention generally to the most modem and approved practice.

We have dealt with steel as the material in general use, and not, as heretofore, an exceptional thing to be found only in high- class structures ; the Tables of Weights, &c., are, therefore, given fully for this material.

Inasmuch as the practice in a considerable part of the Mer- cantile Marine is now more nearly approaching that followed in Naval ships, as to speed and economy of weight, than was formerly tne case, the information and formulae pertaining to light fast-running machinery have been elaborated and based on the most recent practice of the leading firms of Manufacturing Engineers.

In conclusion, we trust that the book may be received favour- ably, and found of use by practical men, and that any short- comings may be overlooked on the score that it is the production of the spare moments of busy men, rather than of those having ample leisure.

A. E S. H. M. R. October 1893.

V

^

PREFACE TO THE FIFTEENTH EDITION.

-M-

This is the Fifteenth Edition of the Pocket-book which was projected just thirty years ago, so that on the average a new edition has been published at intervals of two years. Each of these editions, by amendments and additions, has been brought thereby up to date, so as to accord with the best practice of the day as quickly as possible. This process is always a somewhat troublesome task for the Author and a more or less costly one for the Publishers ; it would have been at one time much easier for both to merely reprint some more copies as the others were sold out. It has been, however, a satisfaction and reward to both Publisher and Author to find their enterprise and efforts rewarded by such a continued demand as to necessitate so many editions.

This new edition, however, has required a more drastic and extensive treatment than usual, inasmuch as so many of the old rules of the Board of Trade, of Lloyd's Register, of the British Corporation, and of the Bureau Veritas have been superseded by the new unified rules based on the recommendations of the British Marine Engineering Design and Construction Committee, and now adopted by these four authorities. This change has also necessitated a recasting of the tables and schedules based on the^e new arrangements.

The rules formerly in force in Government shipping circles in Germany have been expunged from this edition, as apparently they are no longer in general use there. Moreover, there is reason to anticipate that the recommendations of the British Marine Engineering Design and Construction Committee will be taken as the basis for those to be formulated there shortly.

The rules and regulations laid down for the guidance of the responsible marine surveyors in the United States of America are now given in a somewhat condensed form in the Appendix.

They differ considerably from those obtaining in this country by giving more permissive terms, and leaving much to the judgment of the designer and manufacturer. In passing it may be perhaps not out of place to note that much is likewise thereby added to their responsibilities.

vii ^

Till PREFACE.

Additions to the text in various parts have been made as a consequence of the extended experience with modem boilers, as also with machinery of every kind. It may be noted that while geared turbines and internal combustion engines of various sorts and designs are very much to the front now and continue in considerable demand, the triple and quadruple compound reciprocators continue, notwithstanding, to be held in high esteem by those who are of opinion that rate of consumption of fuel is not the only criterion of value. For the ordinar}' tramp cargo ship these steam engines are considered to be the most appropriate, as with them any fuel that will raise steam can be used, and besides their auxiliary machinery is such as to require small space and not much attention when at work. For the passenger ship oil fuel is, of course, the best in every way, and lor steam raising it may be of a quality and cost very different from what the internal combustion engine requires for continued good working.

The saving in space occupied by the machinery, and the reduc- tion in the engineers' crew make the internal combustion engine so attractive a proposition that most builders of marine machinery have now placed themselves in a position to supply them. It is to be regretted, however, that they mostly seem unable or unwill- ing to do so without making use of the patents and designs of foreign inventors. It is to be hoped, therefore, that those who have been content to develop those of British origin will meet with the success that their enterprise deserves.

The opposed piston oil engines and the double-acting oil engines are now being experimented with, and it will be interesting to follow their course, as it has been in the past to follow that of the various types of steam engine from the time when the S.S. Comet made a start over a hundred years ago.

A- E. S.

January 1922;

GENERAL TABLE OF CONTENTS.

-♦♦-

PAQBS

Prime Movers on Shipboard.— Steam-driyen Reciproca- tors, Internal Combustion Reciprocators : Turbines: Combinations : Geared Turbines : Multiple Screws, , 1-2

Engine Power Measurements. — Nominal Horse-power, various Rules for : Estimated Horse-power : Normal I.H.P. : Standard sizes of Cylinders of N.E. Coast Makers : Board of Trade and Lloyd's Rules for N.H.P. : Indicated Horse-power, Shaft Horse-power, Nett Horse- power, Thrust Horse-power, ka, : Mean Pressure in Cylinder and Effective Pressure on Piston as shown by Indicators: Torsion Meters and Application of for Shaft Horse-power, ..... 3-17

Efficiency of Marine Machinery. — Boiler, Steam, an4 Thermal Efficiencies : Mechanical and General Efficiency : Propulsive Efficiency : Froude's Curves : Friction : Ex- periments on Friction by various Scientists : Maximum output of Energy from a pound of Steam : Effect of Jacketing on Efficiency, ..... 17-27

Propulsion of Ships and Resistance. — General Resistance, Residual Resistance : Admiralty Formulae, derivation of them : Sir William White's Observations on Speed and Power : Cruiser and Destroyer Tests at varying Speeds : Results of Steamship Trials at ordinary and at very high Speeds by Reciprocators and Turbines: Eirk*s Method of Analysis of Form: Table of Appropriate Angles of Entrance : Wetted Skin, Mumfora's, Kirk's, and Seaton's Rules for : Seatou's Rules for Co-efficients of Form and Speed Factors : Curves of Power, &c. : Model Experiments : Co-efficients of Fineness : Friction of Im- mersed Surfaces: John's Co-efficients for computing Horse-power : True Mean Speed : Relation of Speeds and Powers: Tables of Times and Speeds: Table of Two- thirds Powers of Numbers from 100 to 56,000, . 27-56

Compound Engines. — Multiple and Simple : Advantages of Triple over Simple Compound in Loads and Consump- tion of Steam : Cylinder Ratios in various Compound Engines : Mercantile and Normal Cylinder arrangements, 66-66

ix

X

CONTENTS.

Steam Expanding and doin^ Work.— Mean Pressure, equivalent in Compound Engines : Mean Pressure, Rules for : Steam Expansion, Isothermic and Adiabatic : Maxi- mum Work : Table of Steam used Expansively : Effect of Clearance, Compression : Tables of Mean Pressure, taking account of Clearance ; Mean Pressure expanded Adiabatic- ally : Ratio of Mean Pressure in Practice to the Theoretical : Trials of Marine Engines, showing Mean Pressures,

Piston Speeds and Revolutions of Engines. — As in Prac- tice m the Navy and Mercantile Marine with various kinds of Engines : Rules for rate of Revolutions, Stroke of Piston, ko. , .

Cylinders.— Diameter of: Sizes of Ports, &c. : Flow of Steam : Ratios of Pipes and Passages : Strengths of : Thickness of Barrels and Liners, Steel and Cast Iron: Cylinder Ends and Covers : Cylinder Valve Boxes, kc : Safety and Escape Valves : Drain Cocks : Starting and Auxiliary Valves : Column Feet and Bolts : Horizontal Engines : Oscillating Cylinders : Clearance of Pistons : Stuffing-boxes and GKands : Studs and Bolts,

Pistons. — Cast Iron and Cast Steel : Proportions and Scant- lings : Forged Steel : Fittings and Details : Junk Rings and Packings, ......

Piston Rods. — Loads and Stresses: Proportions: Naval and Mercantile Practice: Fitting to nstons: Guides and Guide Blocks : Fittings, &c. , .

Connecting^- Rods. — Loads and Stresses: Proportions: Gud- geons : Brasses : Caps and Bolts : Scantlings of Bearings and Brasses, ......

Shafting^. — Loads and Stresses: Bendine and Twisting Moments : Torsional Stiffness : Solid and Hollow Shafts : Shafts of Screw Engines and Paddle Engines: Crank- shafts: Equivalent Twisting Moments: Curves of Inertia Forces, Effect of on Shafts: Crank-pins and Main Bearings, Surfaces: Multiple Cranks, Effect of: Crank- arms: Shaft-coupling Bolts: Built-up Crankshafts: Crankshafts of Paddle Engines : Keys on Shafts : Board of Trade Rules for Shafts : Lloyd's Rules,

Thrust Shafts and Blocks.— Loads and Stresses : Indicated Thrust : Effective Horse-power producing Thrust : Pres- sure on Collars*: Scantlings : Types of Blocks, .

Stem-Tubes.— How Made and Fitted: Proportions and Scantlings : Stern-bushes : Length of Bearing : Stuffing-

DOX , &C. ,. . . . . . •

Main Bearingfs of Crankshafts. — Arrangements of: Caps and Bolts: Loads and Stresses: Brasses, Types and Fitting: Materials: Engine Frames, Design, &c.: Columns, Loads and Stresses, « . . • .

PA0E8

66-76

76-78

78-105 106-113 118-116 116-122

122-189 189-142 142-145

145-149

CONTENTS. Zi

PAaiS

Condensers. — ^Gapacity of Jet Condensers : Injection Water : Low-pressure Steam, Properties of: Surface Condensers : Effect of Vacuum on Consumption : Forms and Arrange- ments, Weir's, Morison's : Cooling Surface : Tempera- ture of Sea-water in yarious purts of the World : Cooling Water, Quantity and Application: Condenser Tubes, Sizes and Fitting of: Tube-plates : Number Tubes per square foot : Devils and Fittmgs, . . 149-158

Air Pumps.— TVpes of: Method of Working: Size of: Weir's Dual Pumps : Vacuum Augmenters : Bods, Bolts, &c : Loads and Stresses : Pump Barrels, &c. : Scantlings of : Valves, ko. : Speed of Buckets : Suction and Dis- charge Pipes : Air Escapes, .... 158-168

Cooling water Pumps. — Types of: Methods of Working: Capacity: Reciprocating Pumps, Details of: Valves, Beds, Pipes, ko. : Centrifugal Pumps : Sizes of Cylinders, Impellers, Pipes &c., . . . . . 163-168

Feed and other Pomps— Gross and Nett Feed-water: Capacity of Pumps : Valves, Rods, &c. : Suction and Delivery Pipes : Feed Tanks : Reserve Tanks : Feed Heaters : Board of Trade Rules : Lloyd's Rules for Feed Pumps, ....... 168-172

Bilge Pumps, Pipes, and Fittings. — Capacity of: Boxes, Strainers, &c. : Directing Boxes : Board of Irade Regula- tions: Lloyd's Rules, ..... 172-175

Pump Levers and Gear. — Arrangements: Sixes: Loads and Stresses : Links, Pins, and Urossheads, Surfaces and Sizes of: Details and Fitthigs, .... 175-177

Slide Valves for Steam Distribution, &c. — Travel : Single and Double Ports : Surface for Rubbing : Relief Rin^ : Port Openings and Leads : Valve Proportions : Tnck Valves : Piston Path Diagram : Zeuner's Dia^m for Common Valve Motion: Diagram showing Effect of ** Notching up " (a) " Open " Rods, (6) " Crossed " Rods : Obliquity of Eccentric Rods: Diagram of Oscillating Cylinder Valve Motion, ..... 177-186

Valve Gears. — Loads and Stresses : Valve Rods, Rules for : Guides : Links of various Kinds, and their Scantlings : Position of Suspension Pins : Proportions of Double-bar Links : Eccentrics, Construction and Scantlings : Straps and Rods : Joy's Valve Gear, Diagram of, . . 186-198

Reversing Gears for Valve Motions. — Types compared : Direct and All-round Gears : Weigh Shafts, sizes of: Steam Cylinders for : Worm Wheels of All-round Gears : 198-200

Steam Turning Gears.— Speed of: Steam Cylinders for:

Worms and Wheels : Construction and Scantlings, . 200-202

Screw Propellers.— Numbers of Screws : Numbers of Blades to each : Shape of Blades : Section of Blades : Materials

Xii CONTENTS.

PAGBS

of Screws : DimensionB of Screws : Diameter : Pitch Ratio: Surface of Blade: Ratio of: Thrust: Slip, Real and Apparent : Rules for Diameter Pitch, Surface, &c. : Acting Surface: Scantlings: Materials: Attachment of Blades : Weight : Bosses, Studs, &c. : Particulars of various kinds of Screws, ..... 200-214

Paddle- Wheel Propellers.— Common Radial: Effective Diameter : Thrust : Area of Floats : Slip, Apparent and Real : Numher of Floats : Scantlings of Floats : Design of Wheel : Wheel Frames, Scantlings of : Shaft Bearings and Feathering Gear, ..... 214-222

Sea Valves for V^ter Supply, &c. — Naval and Mercantile :

Fittings and Materials, . . . . 222

Steam Turbines. — Types used for Propulsion of Ships : Re- versing : Efficiency : Arrangements : Simple : Com- gmnd, Division over two or more Shafts : Geared : vdraulicTi'ansmission : Electric Transmission : Methods followed in Naval and Mercantile Ships : Combination with Reciprocators, R.M.S. Olympic, S.S. Otakii Geared Turbines in S.S. Vespasian, S.S. Nor- mania I Comparison of two Twin- Screw Reciprocating Engine Ships with S.S. Sarnia, ordinary Turbine, and S.S. Normania, Geared Turbine driven : Proportions of Screw Propellers for Turbine-driven Ships : Pressures on Journal of Turbine Shafts : Diameter of Shafting, Board of Trade and Bureau Veritas Rules for : Rotor Drums : Bate of Revolution : Blades of Turbines : Area through Blades : Diameter of Rotors : Exhaust Passages : Leak- ages : Water Tests, Admiralty, Board of Trade, &c. : Weight of Installations : Steam Consumption, Power de- veloped, how measured: Torsion Meters: Shaft Horse- power : Consumption of S.S. LusiUiniaBX various Speeds, also of S.S. Otaki, H.M.S. Amethyst \ Trials of Samia, Normania, H.M. Cruisers **City" Class, S.S. Beina Victoria Eugenia : Caimcross and Caimgowan com- pared, ....... 222-238

Internal Combustion Eng^es.— Various kinds: Gas, Petrol, Paraffin, and Heavy Oils : Oil Fuels used in such Engines: Values: Oil Engines Classified: Diesel and Semi-Diesel Engines: Two- and Four-stroke Cycles: Double-acting Oil Engine : Number of Cylinders : Re- versing of Propeller : General Design : Cylinders : Pistons : Guides : Size of Shafting : Lloyd's and Bureau Veritas Rules for Shafts: Auxiliaries necessary for Oil Engines : Fuel Consumption of Diesels : Consumption at various Powers : Trials of various Oil Fuels : Efficiency, Mechanical, Thermal, and General : Mean Pressure : Rate of Revolution : Burmcister & Wuin*s Practice : Augsburg-

OONTBNTS. xiil

PAGX8

Niimberg Ga's Practice: Salzer's Practice: British Practice: Weights of Oil Engines, Space occupied by: Advantages of Diesel's: Indicated Horse-power Formulse: Cylinder, Thickness of: Trials of Diesel Engine at Full and Slow Speed : Trials of S.S. Eavesione, Selandia, &c., &c., . . . . . 238-262

Motor Boats, &c., usingf Petrol. ~6oard of Trade Rules for: Lloyd's Rules for Petrol and other Oils on Ship- board, ....... 262-258

Superheated Steam. — Modem Practice: Economy: Maxi- mum safe Temperature: Specific Heat of Superheated Steam : Total Heat of : Transmission of Superheated Steam: Maximum Work of: Heating Surface required for Superheating, ...... 268-262

Skin Fitting and valves.— Blow-otf Valves : Method At- tachment to Skin, Naval and Mercantile : Discharge Valves : Board of Trade Regulations : Lloyd's Rules : Details and Fittings, ..... 262-266

Results of Trials of Eng^ines.— Three-crank Triples : Four- crank Triples : Four-crank Quadruples, . . . 266-268

Wire Gauges.— Various and their Equivalents, . . 270-271

Copper Pipes.— Suitable to various Conditions, . . 272-273

Wrought- Iron Pipes.— Suitable to various Conditions, . 274

Copper Pipe Flanges and Fittings.— Scantlings and Pro- portions, ....... 276-276

Bronze and Cast-Steel Pipes. — ^Theoretical and Practical, . 277

Pipes in General — Board of Trade Rules: Lloyd's Rules: Expansion by Temperature : Safety Devices : Steel Steam Pipes: Thickness of Steel Pipes in Practice: Solid- drawn Feed and Steam Pipes : Welded Pipes : Exhaust Pipes : Bendine of Solid-drawn Pipes : Flanges : Admir- alty Tests of Solid-drawn Steel Pipes, also of Welded Pipes, ....... 278-286

Stop and Regulating Valves.— Construction : Details and

Fittings, ....... 286-287

Balancing Engines. — Various Forces: Methods of Static Balance : Dynamite Balancing : Inertia Forces : Yarrow Schlick • Tweedy System of Balancing four Crank Engines, ....... 287-^96

Geometry of Balancing Engines, .... 296-298 Boilers. — Fuels, various Solid and Liquid, their Characteristics and Values : British Thermal Unit : Mechanical Equiva- lent of Heat : Specific Heat : Total Heat of Combustion : Air required for Combustion : Composition of Fuels, Liquid and Solid: Oil Fuels used in U.S.A. Navy: Viscosity of Oil Fuels : Lloyd's Rules for Stowing and Using Oil Fuels : Admiralty Conditions of Contract for Oil Fuels : Rates of Combustion in Practice, . . 298-30©

xiv CONTENTS.

PAOBS

Boilers and their Fittingfs.— Efficiency of Grates : Gbimney Draught: Flow in Funnels: '*Head" required for Draught : Fuel Consumed : Size and Height of Funnels : Table of Funnel Capacities: Scantlings of Funnels and Riveting : Forced Draught : Naval : Howden*s System : Results of Forced Draught: Air Pressure in Boiler Booms : Rates of Combustion and Evaporation, Practical Examples of: Express Boilers: Water Consumption of H.M.S. Diana, R.M.S. LusUaniaf and various other Ships : Domestic Uses, ko,, . . . . 309-321

Boilers.— Various Types and Designs of: Tank and Water- Tube Boilers : Cylindrical, various Sorts : Gunboat, Loco- motive, Double-ended' Water-Tube Boilers, {a) Large Tube, {b) Small Tube: Yarrow, Babcock, Niclausse, Hohenstein, Miyabara, Mumford, White-Forster, Thorny- croft, &c., &c. : Total Heating Surface and Weight of Boilers, ....... 821-325

Boilers. — Efficiency of various Types : Examples of, . . 326

Boilers. — Evaporation, Heating Surface, &c. : Efficiency of: Materials of Construction : Condition of Heating Sur- faces : Circulation of Water : Tubes, sizes of : Water per pound of Fuel: Equivalent Evaporation from and at 212* F. : Examples of various Tank Boilers, . . 827-332

Boilers, Proportions of. — Furnaces, Size and Number of: Total Heating Surface Required for Various Services: Examples of Latest Practice: Water Consumption for Several Departments on Various Services : Auxiliary Machinery and Domestic Demands : Steam Room Allow- ance : Water Spaces : Pitch of Tubes: Multipliers to find Equivalent Evaporation : Weights of Various Installa- tions : Various Designs Compared for Weight, . . 832-339

Boilers of Steel, Construction of. — Admiralty Tests of Steel : Board of Trade Tests and Conditions for Steel Materials, Plates, Forgings, Angle and Plain Bars, Rivets, Forgings, Castings, Tubes, Solid and Lap-welded, &c. : Board of Trade Conditions for Construction : Cylin- drical Shells: Riveting of Various Kinds: Differing Thickness for Varying Tensile Strengths : New Board of Trade and Lloyd's Rules for Shells, and Quality of Steel : Tests for Boiler Material required by Lloyd's : Working Pressures : Riveting : Flat Surfaces and Stays, Board of Trade Rules for, with Tables: Dished Receiver Ends, ko. : Flat Surfaces and Stays, Lloyd's Rules for : Plates in Compression, Board of Trade and other Rules for: Girders and Stays : Stays and Tubes, Admiralty, Board of Trade; and other Rules for : Tables of Surfaces : Furnaces of all Kinds, Board of Trade and other Rules for : Testing by Water, ..... 840-376

OONTBNTS. XT

PAOBS

Evaporators. — Board of Trade Roles and Regalations, . 876

Boilers, Construction. — Lloyd's General Rules for, . . 879

Boilers, Construction. — Board of Trade Rules for Shell

Joints : Examples of Various Kinds of Riveting, . . 380-889

Boiler Work. — Supervision of, as required by British Admiralty, and the I^ocedure in Manufacture: Treat- ment of Mild Steel by Heat : Pickling Processes, . 389-892

Boiler Mounting's and Fittings. —Stop Valves: Steam passed through pipes of vanous sizes : Safety Valves, Rules of Board of Trade and B.M.E.D. & C. Committee, kc. &c. : Spiral Springs, Rules for : Feed Valves and Pipes: Blow-off and Scum Valves: Water Gauges: Weight of Water at Varying Temperatures : Circulating Apparatus : Board of Trade Regulations for Mountings, &C. : Lloyd's Rules for same, .... 392-408

Furnace Fittings. — Doors, Size and Construction : Fire-bars :

Bridges, ....... 408-409

Ladders and Platforms. — Proportions and Scantlings, . 410

Eng^e and Boiler Seatings.— Arrangement and Scant- lings, Screw Engines, Paddle Engines and Thrust Blocks : Holding-down Bolts : Stavs : Boiler Seatings : Methods of Securing Boilers : Lloyd's Rules for Seatings, Bearers, Beams, Bulkheads, Shaft Tunnels, . . . 411-414

Lloyd's Rules. — For Valves in Bulkheads^ Openings in

Decks, Coamings to Hatchways : Deck Casings, . . 414-417

Steam Trawlers.— Lloyd's Rules for Engine and Boiler

Rooms, .....•• 416

Pumps for Bilges, &c.— Lloj^d's Rules for Sluice Valves,

Sounding Pipes, Suction Pipes, Bilge Injection, &c., . 417-419

Surveys of Machinery. — Lloyd's Regulations for, . . 419-421

Spare Gear.— Lloyd's Requirements, . . . 421-422

Board of Trade General Rules and Regulations for Machinery Department. — Auxiliary Engine Suctions : Bilge Injections: Spare Tiller: Rudder Chains, &c. : Steering Engine Pipes : Steam Steering Engine Gearing : Fire-hoses and Fittings : Stand-pipes and C^ks : Chock- ing Boilers, ...... 422-426

Spare Gear desired by Board of Trade.— Main Engines:

for Distillers : Survey of Distillers, . . . 426-428

Chains and Ropes. — Admiralty Tests: Lloyd's Tests: Weight of Breaking Strengths : Special Flexible Wire Ropes: Hemp Ropes: Bullivant's Special Products: Admiralty Tarred Cordage, .... 429-436

Strength of Materials. — Cast Iron of various kinds : Iron Mixtures: Admiralty Requirements of Cast Iron: Wrought Iron of various Kinds and Qualities : Cast Steel : Admiralty and Lloyd's Tests for Steel Castings : Board of Trade Tests for Steel and Malleable Cast Iron : Steel

xvi CONTENTS.

PAGES

Bars and Plates: Admiralty, Lloyd's, and British Cor- poration Tests for Wrought Steel, . . . 436-447 Materials. —Copper, Admiralty Specification: Common Bronze or Gun-metal ; Admiralty Bronze : Phosphor and other Special Bronzes : Brass and Various Yellow Metals : Aluminium and its Alloys, &c. , .... 447-452

Composition, Properties, and Costs of Various Metals, . 453-457 Plates, Bars, Rolled Shafts, &c.— As manufactured in Great Britain, and the £xtras chargeable and other Conditions, ...... 458-461

Beams and Girders. — Effects of various Loads, . .463-470

Test Pressures on Flat Surfaces (Maximum Fluid), . . 471-473

Effect of Temperature on Metals, .... 474-477

Weights of Materials, &c., ..... 479-495

Weights, &c., of Machinery, .... 496-497

Water, Fresh and Salt. — Information on, . . . 498-502

Oils and Lubricants. — Viscosity: Specific Gravity: Flash- points of, • . . . . . . 502-504

Friction.— Co-efficients of, &c., . . . . 504-505

Conductivity of Metals. — Thermal, Electric, and Acoustic, . 606

Fuel Consumptions. — Solid and Liquid, . . . 508-509

Thermometers. — Fahrenheit, Celsius, and Reaumur com- pared, ....... 510-516

Steam, Saturated.— Properties of, .... 517-525

Knots, Miles, and Kilometres compared, . . 527-530

Metrical and British Standard Measures compared, . 530-546

Circles. —Properties : Tables,. .... 547-564

Spheres and Cones. —Properties : Tables, . . . 565-566

Square Cubes and Roots of Numbers, . . 567-611

Fourth Powers of Numbers, ..... 612-613

Hyperbolic Logarithms, ..... 614-616

Nomenclature and Definitions, .... 617-618

British Corporation.— Rules and Regulations for Machinery, 621-640 Bureau Veritas. — Rules and Regulations for Machinery, . 641-666 U. S. A. Government— Rules and Regulations for Machinery, 667-675 Electric Lighting, &c. — Lloyd's Rules and Regulations

for, ■ . . . . . . . 672-677

Refrigerating Machinery.— Lloyd's Rules and Regulations

for, ...... . 678-686

Steering Gear.— Lloyd's Rules and Regulations for, . 686-687

Lloyd's Instructions to Surveyors re Tests, &c. , . . 688-694

Lloyd's Rules for Diesel and other Oil Engines :—

(a) Nominal Horse Power ; (6) Rules for the Construction

and Survey of Diesel Engines^ and Auxiliaries, 695-704

Lloyd's Rules for Screw Shafts and Stern Tubes, . 705

Distances of Various Principal Ports, &c. . 706-718

Standard Specification of North -East Coast Engineers for

Triple Compound Engines, . • • . 719-721

CONTENTS. XVU

PAQIS

Russian Weights and Measures compared with British

and Metrical, ...... 725-726

Hydraulic and Steam Tests of the Admiralty and Register

Societies, &c. , . . • . . . 727-729

Melting-points of Various Metals, 780

Lloyd's New Unified Rules for the Survey and Con- struction of Engines and Boilers of Steam Vessels, . 731-756

Weight of Metal Plates per Square Foot, 757 «

Index, . * . . . . . . 758-770

XX

LIST OF TABLES.

No.

LXXXIII. LXXXIV.

LXXXV.

LXXXVI.

LXXXVIL LXXXVIIA. LXXXVIIB. . LXXXVIIO. LXXXVIlD. LXXXVIIB. LXXXVIIL

LXXXVIIIA.

LXXXIX.

xc.

XCI. XCII. and XCIIA. XCIII.

XCIV.

xcv.

XCVI.

xcvn.

xcvin.

xcix.

xcixa.

c.

CI.

CI A.

CII. CIIL CIV.

cv.

CVL

CVIL

CVIIL

CIX. CIXa.

ex.

CXI. CXII.

Subject Matter.

Thickness of bronze and cast-steel pipes, T pieces, Ac.

„ of cold solid -drawn steel st«am and feed

pipes in 64ths of an inch, ....

„ of welded or riveted steam pipes in 64th8 of

an inch,

„ of solid-drawn or riveted exhaust pipes in

64ths of an inch,

Composition and value of fuels,

„ „ of liquid fuels, ....

Consumption of various liquid fuels per 24 hours, . Composition, Ac. of certain liquid fuels as in practice, .

Oil fuels as used in U.S.A. Navy boilers

„ „ viscosity of,

Capacity of funnels for quantities of fuel burnt per

hour

Pitch, ^c, of riveting for funnels, casings, Ac

(Admiralty)

Results of trials of certain boilers at full powers, . Rates of combustion and evaporation (tank boilers), . Express boilers, particulars of surface, weight, Ac, Water-consumption trials of H.M.S. Diana and S.S.

Lugitania^

Consumption of water and fuel on trials of various

ships,

Thermal efficiency of various boilers, . . . . Particulars of destroyers built by Messrs Tarrow A Co., Comparison of water tube boilers with others in various

ships,

Leading jiarticulars of some boilers madfe in recent

years

Particulars of laige modem cylindrical boilers, scant-

Am^By • • • flr ••••••

Total heating surface per I.H.P. of various ships, . Allowance of steam room in boilers, .... Multipliers for converting weight of water evaporated

to the equivalent from and at 212* F., . . . . Relative weights of various boiler installations, . Ck>mparison of steel boilers of various designs. Board of

Trado rules for 160 lbs.

Admiralty tensile tests for steel boiler materials, . Board of Trade tensile tests for steel boiler materials. . Relative thickness of boiler plates for different tensile

strengths,

Board of Trade constants for flat surfaces,

Pitch of stays and area of flat surfaces of combustion

chambers (B.M.E.D. A C. Committee), . Pitch of stays supporting flat plates not exposed to

flame (B.M.E.D. & C. Committee rule), Pitch uf stays supporting flat plates when fitted with

washers (B.M.E.D. & C. Committee rule), . Working pressure, boiler shells of 28 tons tensile steel, .

»» •» »» »» •** It i» •

Lloyd's old rules for flat surfaces,

Corrugated furnaces, working pressure in lbs. per

BCJ« I Is CXly ••••••••••

Surface of plate supported by one screwed stay (B M.E.D. & C. Committee rule)

LIST OF TABLES.

XXI

Ko.

CXIIL

CXIV.

CXV.

CXVI. and

CXVII.

CXVIII.

GXIX.

CXX.

CXXI.

CXXII.

CXXIIL

CXXIIIA.

CXXIV.

cxxv.

CXXVL

CXX VIA.

CXXVII.

CXX VIII.

CXXIX.

CXXX.

ex XXL

CXXXII.

CXXXIIL

CXXXIV.

cxxxv.

CXXXVI.

CXXXVII.

CXXX VIII.

CXXXIX.

CXL.

CXLI.

CXLH.

cxLin.

CXLIV. CXLIVA.

cxlivb.

CXLIVo.

CXLIVd.

CXLV.

CXLVI.

CXLVIL

CXLVIIA.

CXLVIIB.

CXLVIII.

CXUX.

CXLIXA.

CL.

CU.

CLII.

CLIII.

CLIV. CLV.

Subject matter.

Surface of plate supported by one Btav of 28 tons tensile steel, B.M.E.D. & C. Committee rule, .... Tests (mechanical) of boiler materials, .... Joints of plates, their seTeral kinds and strengths.

Quantity of steam passed through pipes

Safety-valve springs, sizes of, by Board of Trade rules, . Weight of pure water at different temperatures, . Safety- valve areas for different pressures, Board of

Trade

Ladders and gratings, scantlings of , . . . . Sizes of bilge suction pipes ^Lloyd's rules). Admiralty tests, Ac., of stud-link chain cables,

.. „ „ short-link chains, •

Lloya's ,. „ stud-link chain cables,

Admiralty flexible steel wire ropes,

Breaking strength of steel wire hawsers (Lloyd's), . Special flexible steel wire ropes, . . BuUivant's steel wire ropes, galvanised, .... Mild plough steel wire crane ropes (Black), .

Admiralty tarred hemp cordage,

Composition and qualities of cast iron, .... Comparative requirements for steel castings, . Composition of white (bearing) metals, ....

Properties of various metals,

Prices of materials

Safe working stresses on various metals, ....

Bending moments, <fec., of beams,

Moments of inertia, modulus, &;c., of some sections. Forms of beams of uniform strength, .... Greatest fluid test pressure on flat surfaces of cast iron, Greatest fluid test pressure on flat surfaces of steel and

bronzes,

Greatest nuid test pressure on flat surfaces of bronze

castings,

Expansion of metals, &c., for rises in temperature. Effect of temperature on certain metals,

Melting-points of various metals,

Melting-points of various alloys,

Specific heat of various materials,

Thermal conductivity of metals,

Electrical resistance of metals,

Weights of various materials,

>¥eight of round and square bars of wrought iron,

,. „ „ mild steel,

„ round steel shafts,

„ „ hollow steel shafts, . . . .

„ flat bars of wrought iron,

„ „ mild steel,

„ large rectangular section steel bars,

,, angle bars of wrought iron, ....

„ „ mild steel,

,, boiler tubes of wrought iron, .... Standard list of sizes and prices, &c., of welded boiler

tubes

Weight of large steel tubes

„ seamless copper tubes,

I

87S 886 880

898

897 400

404 410 419 429 429 480 431 482 438 484 435 436 437 446 468 454 456 462 468 467 469 471

472

478

474 475 476 476 477 477 478 479 480 481 482 482 483 484 485 486 487 488

490 491 492

Y

XXll

LIST OP TABLES.

No.

CLVL

CLVII.

CLVHL

CLIX.

CLX,

CLXI.

CLXII.

CLXIII.

CLXIV.

CLXV.

CLX VI.

CLX VII.

CLXVITI.

CLXIX.

CLXX.

CLXXI.

CLXXII. CLXXIII. CLXXIV.

CLXXV. CLXXVI.

CLXxvn.

CLXXVIII. CLXXIX.

CLXXIXa.

CLXXX. CLXXXL

cLxxxn.

CLXXXIIA.

CLXXXIII.

CLXXXIV.

CLXXXV.

CLXXXVI.

CLXXXVII.

CLXXX VIIA.

CLxxxvin.

CLXXXIX.

cxc.

CXCL

CXCII.

CXCIII.

CXCIV.

cxcv.

CXCVI.

CXCVII.

CXCVIIA.

CXOVIIB.

CXCVIII.

CXCIX.

cxcixa.

CC.

CCI.

COIL

Subject Matter.

Whitworth's standard gas threads,

Weight of brass condenser tubes,

„ lead pipes

,1 sheet metals,

„ engines and boiler installations of all kinds,

Surface of tubes in square feet,

Weight of fresh- water per volume,

„ salt ,, „

Composition of solid matter in feed waters, .

Quantity of solid matter in sea-waters and various seas.

Composition of solid matter in sea-waters.

Weight of cubic foot of sea-water at various ports, <ftc..

Boiling-points of sea- waters of different densities,

Viscosity of oils at various temperatures,

Characteristics ol various lubricating oils of good quality,

Boiling, setting, and flash points of various oils, &c., .

Co-efficients of friction of various substances.

Conductivity, acoustic, electrical, thermal, of metals, .

Various gases, properties of,

Pressure of water due to various " heads,"

Coal consumed per day at various rates of consumption,

Oil fuels ., ., „ „

Comparison of thermometers,

Properties of saturated steam, temperature, density, heat, <frc

Total heat of evaporation from and at differing tempera- tures,

Knots, miles, kilometres, ftc, ......

Elilometres and Admiralty knots,

Millimetres and inches.

English feet and French metres

Decimal equivalents of fractions of an inch, .

Metrical „ „ „ • . .

Square feet and square metres,

Square metres and squure feet,

English pounds avoirdupois and kilogrammea,

Kilogrammes and pounds avoirdupois ....

Lbs. per sq. in. and kilogrammes per sq. centimetre, .

Kilogrammes per sq. centimetre and lbs. per sq. in., .

Kilogrammes per square millimetre and tons per eq. in.

Areas of segments of circles,

„ of circles,

Circumferences of circles,

Areas and circumferences of small circles.

Spheres, volume and surface of, also that of cones.

Squares, cubes, square roots, cube roots, and reciprocals.

Fourth power of numbers,

Fourth root of numbers,

Fourth power of shaft diameters,

Tons of water delivered through pipes with loss of head =6 lbs.,

Hyperbolic logarithms

Power transmitted per revolution of shafts, .

Horse power transmissible by shafts, ....

Insulating materials for boilers

Refractory materials for furnaces . . . .

Weight of metal plates per square foot ....

t

494 494 496 496 496 498 498 490 499 600 600 601 602 602

603 604 604 606 606 507 608 609 610

617

626 627 630 531 536 530 580 540 541 542 548 544 545 546 547 650 557 564 565 567 612 612 613

614 614 616 619 620 620 757

MARINE ENGINEERING RULES

AND TABLES.

MARINE ENGINES-VARIOUS KINDS OR

The prime movers employed on shipboard for driying the propellers are to-day: —

(1) Reciprocating Engines ; (2) Turbines ; (3) Combinations of both.

1. Reciprocating Eng^es are worked by means of steam or the com- bustion within their cylinders of gas or spray from liquid fuels, or the gas from solid fuel.

Steam-drivm reciproeators are direct acting, inverted in the case of screw ships and inclined for paddle ships. They are invariably of one of the compound types — that is, the steam is expanded and acts in a series of cylinders, instead of in one only. Marine engines of all steamers, except very special ones, such as tags, where economy of fuel is not of prime importance, are of the triple or quadruple expansion principle, so that there are three or more cylinders to each. Fast- running engines in express steamers and naval ships, whether triple or quad- ruple, have usually four cylinders operating on four cranks.

Oil-driven reciproeators. — There are two kinds, known generally as the Diesel and the Semi- Diesel ; they both consume heavy oil, but differ fundamentally as to the degree of compression of the air-charge before the liquid fuel is injected. In the case of the Diesel, the air compression (usually 35 atmospheres at least) results in a temperature high enough to ignite the incoming oil spray. In the Semi- Diesel the compression is considerably less, and the temperature is insuflBcient for the purpose of ignition ; in it hot bulb or plate igniters are fitted.

The Semi- Diesel engine works on the two- stroke cycle whereby an explosion occurs at each revolution.

The Diesel engine is sometimes worked on this cycle and sometimes on the four-stroke cycle, with an explosion only at each alternate revolution, that is, at one in four strokes.

In small craft, paraflSn is sometimes used as fuel with engines work- ing on the four-stroke cycle. Generally all these oil engines are single- acting, as double-acting ones have not so far proved to be satisfactory ill continuous running.

1

i BNOINB POWfiB — MEAStJRBMBNT Of.

2. The Turbine is a rotatory engine and essentially a velocit}^ machine, as against the previous kind, which are all actuated, by pressure. It derives its motion and power entirely from the kinetic energy of the steam particles, to which great velocity is imparted by the expansion during the loweiing of pressure from the initial to that at exit to the condenser.

The expansion may take place in one stage, as in the De Laval turbine, or it may be in a series of stages, just as in compound reciprocators.

Other rotatory machines whose motion and power are due to steam pressure acting on pistons or their equivalents nave been tried, but in small units only have they been successful.

3. The combination of a turbine with a reciprocator has been car- ried out on a very large scale in R.M.S. Olympic^ and on other ocean- going steamships of various sizes, all with satisfactory results. By means of the low-pressure turbine the energy remaining in the exhaust steam from a tiiple compound reciprocator is fully utilised, and the very high vacuum so easily and cheaply maintained in a marine con- denser thus made full use of effectively. The saving in fuel by this combination is generally about 15 per cent, over that of the triple or quadruple engine, or there is an increase in power developed to a corresponding extent from the same expenditure of fuel in each case.

Beeiprocators are nearly always connected direct to the propeller shaft- ing, as their rate of revolution is not unsuitable to that of the propellers.

All Turbines are now geared by pinion and wheels to the propeller shaft, so that they may not have so low a rate of revolution as that required for the high eflSciency of a satisfactory screw. The ejQBicienoy of the turbine to be good requires high peripheral velocity or a large number of stages for expansion, the former being desirable.

Ungeared Turbines used to be divided so that small ships had three screws and large full-powered ones four screws. Just before gearing was adopted the twin scrow arrangement, with a complete turbine combina- tion to each, was preferred for ** Destroyers" and ** Flotilla Leaders."

Geared Turbifies may be each divided into two parts, the high pressure and the low pressure. For cargo ships of low power one screw is usual, for higher powers multiple screws obtain, so that Naval ships of very high speed have as many as four screws. The gearing may be single for small powera, but now is usually double for larger powers, and is preferable.

Large ships vnth high power, even when driven by reciprocators, were sometimes designed with three screws both in the Naval and mercantile services, especially in some foreign ones.

ENGINE POWER— MEASUREMENT OF.

Nominal Horse-power, as understood by Watt, was a measure of the commercial value of an engine, being the power it might be expected to develop in ordinary work. Gradually, however, as it became possible to construct boilers to supply steam at higher than atmospheric pressure, the powers developed by engines exceeded the nominal horse-powers.

SNOIN& ^OWBR — ^MBAStmBHBKT OF. 3

until Watt's rule ceased to have this meaning and value, and the general use of the indicator and other means of ascertaining the actual power developed by the engine when working have caused the decline in the use of the expression. But there remains the need for some means of expressing in simple figures the size of a reciprocating engine for purposes of comparison and commerce. There are also other and technical demands for such a denomination, as will be shown.

Thus, for many years, a marine engine was expected to indicate about five times its nominal horse-power. The rule then in use was as follows : —

•»- ^ p __ Sum of squares of piston diameters * ' ~" 30 to 38 (according to district) *

boiler pressure, piston speed, &c., being left entirely out of considera- tion. It is, of course, hardly necessary to say that such a rule was quite useless for any scientific purpose ; whilst, even for commercial purposes, it gave only a very imperfect idea of the relative values of different engines. Its use, however, still survives in some districts, the divisor being 80, the normal stroke '618 of diameter of L.P. cylinder, and the normal heating surface 16 square feet per N.H.P.

The matter was still in this chaotic condition when, in 1888, Mr Seaton, in his "Manual of Marine Engineering," suggested the use of E.H.P., or Estimated Horse-power, which is now calculated in the following way: —

Rule I. Seatm's. E. H. P. = D^xV^xS^R

D is the diameter of L. P. cylinder and S the stroke of piston, both in inches ; P is the absolute boiler pressure ; R, the revolutions per

minute.

For naval ships with overloads, Z= 85,000. „ short passage express steamers, Z = 91,000. ,, long „ ,, Z= 94,500.

,, passenger cargo steamers, Z= 97,000.

cargo steamers, Z = 1 05, 000.

y*

Rule la. Seaton' 8, K H. P. = D^xWPxSxR

(r + 2)x 140,000

WP is the working or boiler pressure,

r is the ratio of the L.P. to the H.P. cylinder capacity.

These formulse give a very close approximation to the horse- power actually indicated when working at full speed.

In 1888, the North-East Coast Institution of Engineers and Ship- builders proposed the following very complete formulae : —

(D2>ys+3H\/P)"

Rule 2. N.E.C. Institution, N.I.H.P. =

100

4 fiNGmB POWftft — MftASUtlBMBNt Off.

Where N. I. H. P. = Maximum normal indicated horse-power, on loaded

trial trip, of surface-condensing screw engines, working at any pressure between 60 and 250 lbs. , under ** normal" conditions. D = Diameter of L. P. cylinder, in inches (if more than

one, D^ must equal sum of squares). S = Stroke, in inches.

P= Working pressure, in lbs., above atmosphere, H = Heating surface of boilers in sq. feet. Pm = Mean pressure, in lbs., referred to L.P. cylinder. Tlie conditions assumed as "normal " are as follows : —That

(1) Steam of all pressures is expanded down to the same terminal

pressure ;

(2) Expansion is effected with same degree of efficiency for all

pressures ;

(3) Piston speeds are proportional to cube roots of strokes, and,

further, actual loaded trial-trip piston speed may be taken

as 144>yS ;

(4) In all cases where relative proportions of engine and boiler

prevent (1) being fulfilled without violating (3), the coal consumption will not be i^ected, but will be constant for the same boiler pressure ;

(5) Boilers are of usual proportions and construction, and the

horse-power proportional to heating surface (H), and to cube root of pressure (^yP) ; and further, actual loaded trial-trip

horse-power may be taken as — ^^ ?

(6) Efficiency of engine mechanism is constant, and the propeller

such that engines will utilize boiler power, referred to in (5), in the manner prescribed in (3) and (4). As a result of (1) and (2), it follows that mean pressure referred to L.P. cylinder (Pm) may be assumed as proportional to cube root of boiler pressure (^^P), and further, that its actual loaded trial-trip value may be taken, without sensible error, as 5 "6 ^5/P.

The normal relation between engines and boilers is expressed by the equation.

H = 5^. ^ 3-25

The results obtained by the Rule 2 for N.J.H.P., if divided by 6, give quantities very near those found by the old nominal horse-power rule.

It is also claimed that, — for machinery of the same type and design, proportions and arrangement, built of similar materials, under similar circumstances, to similar factors of safety, and not differing very widely in size, — the weights and costs will vary almost exactly as N.I.H.P.

For paddle engines the same rule may be used, with the co-cfficieuta

ENGINE POWER — MEASUREMENT OF.

altered to suit the piston speeds usnal for these engines. Assuming that jinder (4), piston speed of paddle engines may be taken at

90 Ays, the rule may, without sensible error, be written, —

Rules. Paddle Engine, N.I.H.P.=^^'^^^^^^^^^

and the normal relation between engines and boilers will be expressed

by-

H=

Da-e/S

6-2

The " Standard practice ** formerly obtaining on the North- East Coast of England for triple compound engines working with steam of 160 lbs. pressure was as in Table I. To-day N.H.P. is not used there; in its place an estimated I.H.P. is taken for cargo steamer engines designed on Standard Rules {vide Appendix L) for a working pressure of 180 lbs. ThisLH.P. is =D«xSxN-^700.

Where D is the diameter of the L.P. cylinder in inches, S is the stroke in feet, and N the revolutions per minute, which by rule = 32(S 4- 4) -r S.

Taking the stroke in inches as S, and combining these, then estimated I.H.P.-D2(Si-|-4)-r262-6.

Table I.— Sizes of Cylinders, &c., and corresponding N.H.P.

I N.H.P.

Diara. of cyls. in inches.

Stroke in ins.

N.H.P.

Diars. of cyla. in inches.

oo ^o

CO —

36 36 39 39 39 39 42 42 45 46 48 .. •

H.P.

M.P.

L.P.

H.P.

M.P.

L.P.

514

53

54

56

57

59

60

63

66

69

71

• • •

20

30

40

50

60

70

80

90

100

110

120

130

8

94 11 124 134 14 154 16

164 17 18 184

13

154

18

20

22

23

25

26

27 •

28

29

30

22 26 30 33 36 38 40 43 45 46 48 50

18 21 21 24 24 27 27 30 30 33 33 33

140 150 160 170 180 190 200 225 250 275 300

• « •

19

20

20

204

21

214

22

23

244

25

26

•• •

314

324

33

34

35

36

364

38

40

414 43

• • ■

Rule 5. Board of Trade Rule for registration purposes : —

^ „ p (3H-hD'4/S)4/F j.^.xi.ir. - ^QQ

where H= heating surface of main boilers in square feet.

D^= square of diameter of low-pressure cylinder, or sum of squares of diameters of cylinders in non-compound engines, measured in inches. 8= length of stroke of engines in inches. P s pressure of main boilers.

ENGINE POWER — MEASUREMENT OP.

Rule 6. Lloyd's Rule for determining amount of survey fees, &c. , is as follows : —

p+c/pys H\ K V 100 isy

N.H.P.

where D is diameter of L.P. cylinder in inches; S, stroke in inches ; H, heating surface in* sq. feet ; P, working pressure in lbs. per sq. inch ; and

fi_ / 340 where boiler pressure is below 160 lbs. ^~\690 ,, ,, 160 lbs. or above.

jr_ ( 1000 „ ,, below 160 lbs.

\1500 ,, „ 160 lbs. or above.

H If the boilers are fitted for other than natural draught, ^ is to be

•a

substituted for — H includes surfaces of tubes, of back tube-plates,

15

and of furnaces and combustion chambers down to level of fire bars.

Since the capacity of the L.P. cylinder is the true measure of the size of the engine, and as the other cylinders have a relation to the L.P. which does not vary largely in any but naval engines ; and, further, as the standard stroke in general practice varies with the diameter of cylinders, the following gives a good criterion of the size of the engine, which may be usefully employed for various purposes : —

Rule 7. Se€Uon*8(2). N.H.P.=DxS-5-X,

where D and S are as before the diameter of L.P. cylinder and stroke in inches, and X a factor which for compound engines is 15, for triples 12 '5, and for quadruples 10*5, and extension of this is —

Rule 8. Seaton's (3). N. H. P. = ^ ^ ^Kf^^ ^^^ *^^ engines where P is the absolute boiler pressure.

ENOINB FOWBtt — UEASURBMBNT OP. 7

Table II.— Nomiiui HorsMkower of Triple Compound Engines (DxS-!-i2-fi).

a

ENGINB POWBB — MEASUREMENT OP.

Table III.— Nominal Horse-power of Quadruple Compound Engines.

^S

Strokes

•

meter Cyliad

•

oa

»

•

•

at

09

S

en

•

•

oa

• IB

00

•

a*

a

a

a

d

fl

Q

a

a

a

C

a

S

p

s

•8 .

•^

•rt

•r*

«^

M«

•»H

•v4

•<M

•■-«

XM

v4

•a

•■>«

5«^

^

t^

o

CO

to

o

04

lO

$

fH

'^

f«

g

C4

04

eo

m

M

M

^

■^

kO

to

«o

^

ins.

86

82

92

103

113

123

133

144

154

• •

• ■

• •

88

86

97

108

119

130

141

152

163

• ■

• •

• •

40

91

102

114

125

137

148

160

171

• •

■ •

42

96

108

1^0

132

144

156

168

180

192

•

• •

44

113

125

138

150

163

176

188

201

• •

• •

46

118

181

144

157

170

184

197

210

• •

• •

48

123

137

150

164

178

192

206

219

233

• •

« ■

50

142

157

171

186

200

214

228

242

257

• •

52

148

163

178

193

208

223

237

262

267

• •

• •

54

154

169

185

200

216

231

247

262

277

293

308

56

160

176

192

208

224

240

266

272

288

304

320

• •

53

182

198

215

232

248

265

281

298

315

331

• •

60

188

205

223

240

257

274

291

308

326

343

62

194

212

230

248

265

283

301

318

337

354

64

201

219

238

256

274

293

311

329

348

366

• •

66

207

226

245

264

283

302

321

339

358

377

390

68

213

232

252

272

291

811

330

349

869

388

408

70

220

240

260

280

300

320

340

360

380

403

420

72

247

267

288

308

329

349

370

391

411

432

74

254

276

296

317

338

369

380

402

423

444

76

260

282

304

325

347

369

390

412

434

456

78

267

290

312

334

356

879

401

423

446

468

80

274

297

320

342

365

388

411

434

457

480

82

281

304

328

351

374

398

421

445

468

492

84

287

311

336

359

883

407

431

456

479 504

1

Summary Rules for Estimating Horsepower.

1. Estimated I.H.P.=5VP+il^xl(Seatou, v, - Manual,"

p. 197). _ _

2. Nominal I.H.P. (Screw Engines) = ^^^^^'^^^^ n/P(N.E. Coast

Inst. E. andS.).

8. Nominal I.H.P. (Paddle Engine) = ^^'^^^ + ^^^ ^"^(N.E. Coast

Inst. E. and S.).

4. Estimated I.H.P.=D2(Sj + 4)-r262-5 (N.E, Coast Engineers, X917).

ENGINE POWER — MEASUREMENT OP.

5. Nominal H. P. (3 H + D^ ^S) x 4/P-T-700 ( Board of Trade).

6. Nominal H. P. = ^('^^^ + ^\ (Lloyd's).

7. Nominal H.P. =D x S-i-X (Seaton, v, ** Manual," p. 196).

8. Nominal H.P. = D x S x VP+T5 -f 150 (Seaton).

d is the diameter of the H.P. cylinder, dj that of the first inter- mediate, etc. , and D that of the low pressure ; S the stroke of piston ; all in inches. P the load pressure on safety valves in lbs. per sq. inch ; H the heating surface of the boilers in sq. feet ; 0 and K are 340 and 1000 respectively when the boiler pressure is under 160 lbs., and 590 and 1500 when above 160. R the revolutions per minute ; and X is 15 for. compound engines, 12'6 for triple, and 10*5 for quadruple. Z varies from 86-000 to 105*000 («. ante).

Table Ilia.— Horse-power in ft. -lbs. of Foreig^n Countries.

Oonntry.

British ft. -lbs. per minute.

Ratio of

foreign to

British.

Eilogrammetres per second.

France ....

Prussia

Austria

Saxony

Hanover

German Empire .

32,552 32,689 33,034 32,668 32,705 33,000

0-9865 0-9900 1-0010 0-9869 0-9906 1-000

76-000 75-325 76-119 75-045 75-361 76-041

Indicated Horse-power. — The indicated horse-power of an engine may be defined as the measure of work done in the steam cylinder, as deduced from the indicator diagrams, and is equal to (area of piston in square inches x mean pressure in lbs. per square inch x number df feet travelled through by piston, per minute) -r 33,000 ; or, —

Rule 9.

I.H.P.=

AxPxS 33,000

Piston speed, S,=: stroke in feet x2x number of revolutions per min.

In the case of engines having more than one 8ted.m cylinder, the I.H.P. of each cylinder is determined separately, and the sum of these is the I.H.P. of the engine.

Where accuracy is required, the sectional area- of piston rod should be deducted from the areas of piston.

Shaft Horse-power is that transmitted by the shaft and is measured by the torque on it. If Tq is the torque in lbs. , 0 the angle of torsion on a length of shaft I inches, whose diameter is d inches, then

10 BNQINE POWER — HBASURBMBNT OF.

6^xd^x revB.

Rule 10. S.H.P.

3-27 xZ

Nett Horse-power is that required to overcome the resistance of the ship only, then if R is the resistance in lbs., S the speed in knots per hour, we get

Rule IX. NettH.P/=.^iS^i580^RxS^

38,000 X 60 325

Tow-rope Horse-power is that required to tow the ship without a propeller, T is the tension on tow-rope in lbs.

Rule 12. TrH.P.=^^.

Propeller Horse-power is that received by the propeller. Thrust Horse-power is that delivered by the propeller for the pro- pulsion of the ship, so that T« is the thrust in lbs.

Rule 13. T,H.P.=?^.

Summarising^.

(1) I.H.P. is the gross power generated.

(2) S.H.P. is the nett power delivered by the engine to the shafting.

(3) PrH.P. is that received by the propeller, being S.H.P. minus the loss at the thrust and other bearings and in the stern tubes.

(4) T»H.P. is that delivered to drive the ship, being PrH.P. less that lost by friction, eddies, etc. , iu its working.

(5) TrH.P. is the thrust H.P. less that lost by the augmented resistance set up by the screw, and is practically nett H.P.

To determine the mean pressure from an indicator diagram the follow- ing is general practice : —

Let fig. 1 represent a pair of diagrams from the L.P. cylinder of a compound engine. Draw two perpendiculars to the atmospheric line AB, one at each end of and touching the diagrams ; divide the space between them into ten equal parts, placing the division marks so that there shall be half a space at each end, and draw a vertical ordinate through each mark ; measure off the breadths of the diagrams at each ordinate to the scale corresponding to the indicator spring and figure them on ends of ordinates as shown, keeping the figures referring to each diagram in a separate column.

The sum of each divided by ten gives two mean pressures, — one of which refers to each side of the piston, — and the mean of these two is the mean pressure required.

Planimeter. — Where there are many diagrams to be calculated, it is quicker to use a planimeter in place of the method ffiven above. The method is as follows : — Measure the area of the figure oy means of the instrument, and divide it by the length AB, when the quotient will be the mean breadth in inches; and this, multiplied by the

BNOINB POWER — MEASUREMENT OF.

11

'* acale" of the spring used (the number of pounds required to compress it one inch) will give the mean pressure required.

The Coffin averaging instrument is a form of planimeter specially designed for dealine with indicator diagrams. It leaves on tne card t^o needle pricks, the distance between which is the mean breadth of

^ •? !& ^

>% «? ^ Ss

^ g $ ^

S S S S fc ^

^ ^ ^ ^ ^ ^

Fio. 1.

S3^

^

I

I

I

11

the figure, — and thus performs mechanically the process of dividing area of figure by length.

The following equivalents may be useful in calculations connected with the above : —

{Pounds per sq. inch x '07 = Kilogrammes per sq. centimetre. Kilogrammes per sq. centimetre x 14 '22 = Pounds per sq. inch.

{Foot-pounds x 7 '233 = Kilogrammetres. Kilogrammetres x *138 = Foot-pounds.

/ Horse-power x 1*0139 = Chevaux. \ Chevaux x *9863= Horse-power.

See also " Tables of Pounds per square inch and Kilogrammes per square centimetre," Table CLXXXVIII.

The Continental ''Cheval'* is equal to 4500 kilogrammetres, or 82,549 foot-pounds per minute, as against 83,000 foot-pounds per minute, --the value of the English horse-power."

The following Table will considerably facilitate the computation of indicated horse-power :—

12

ENOINB POWER — MEASUREMENT OF.

Table IV.— Constant Multipliers for I.H.P.

area of cylinder

■

OoDstants diameter

^000 ; &nd I. H.P s constant X mean preen. X piston speed.

Diameter

Diameter

,

DUuneter

of

Constant

of

Constant

of

Constant

of

Constant

Cylinder.

Cylinder.

Cylinder.

Qylinder.

6

•00086

1634

•00648

84

•02761

60

•08569

34

•00092

%

•00668

34

•02833

61

•08866

Vl

•00100

17

•00688

36

•02916

62

•09149

%

•00108

34

•00708

34

•02999

63

•09447

7

•00116

34

•00728

36

•03084

64

•09748

34

•00126

%

•00749

34

•03171

66

•10065

K

•00134

18

•00771

37

•03268

66

•10368

%

•00143

34

•00792

34

•03347

67

•10684

8

•00162

34

•00814

38

•03437

68

•11006

34

•00162

%

•00836

34

•03628

69

•11332

3i

•00172

19

•00869

39

•03620

70

•11663

%

•00182

34

•00882

34

•03713

71

•11998

9

•00192

34

•00905

40

•03808

72

•12339

34

•00203

%

•00928

34

•03904

73

•12688

3i

•00214

20

•00952

41

•04001

74

•13088

94

•00226

34

•01000

34

•04099

76

•13388

10

•00238

21

•01049

42

•04198

76

•13748

34

•00260

34

•01100

34

•04299

77

•14112

3i

•00262

22

•01162

43

•04401

n

•14481

%

•00276

34

•01205

34

•04604

79

•14854

11

•00288

23

•01269

44

•04608

80

•16232

34

•00801

34

•01314

34

•04718

81

•16615

H

•00314

24

•01371

45

•04820

82

•16003

%

•00328

34

•01428

34

•04927

83

•16898

12

•00842

26

•01487

46

•06036

84

•16796

34

•00867'

34

•01647

34

•06146

86

•17198

1

3i

•00372

26

•01609

47

•06267

86

•17604

%

•00387

34

•01671

34

•06370

87

•18016

13

•00402

27

•01736

48

•06483

88

•18432

34

•00417

34

•01800

34

•05698

89

•18853

3i

•00433

28

•01866

49

•06714

90

•19280

'

%

•00449

34

-01933

34

•05832

91

•19710

1

14

•00466

29

•02001

60

•05960

92

•20146

34

•00483

34

•02071

61

•06191

93

•20687

34

•00500

30

•02142

52

•06436

94

•21030

%

•00517

34

•02214

53

•06685

96

•21480

15

•00535

31

•02287

54

•06940

96

•21937

34

•00653

34

•02362

56

•07200

97

•22394

3i

•00671

32

•02437

66

07464

98

•22869

%

•00690

34

•02513

67

•07733

99

•28328

16

•P0609

83

•02692

58

•08006

100

•23799

H

/00628

}i

•02671

69

•08286

101

•24280

MatNie powktt — HEASURiaiEKt o^.

13

When the effective pressure on the piston at each point in the stroke is required, — as for instance, to calculate the twisting moment on the crankshaft, — diagiams should he constructed from the indicator diagi-ams, as follows : —

First, draw the line of no pressure, CD. Then, dealing with one stroke at a time, the curve EFG represents the varying pressures on one side of the piston, whilst the opposing T>ressures are represented by the curve J KB, which forms a part of the diagram from the other side of the piston.

Draw any ordinate FH, and set off HL=HF - HK ; then L is a point in the required resultant diagram in which any number of other points

Fig. 2.

may be found in a similar way ; at the point H, in the stroke CD, the effective pressure is HL. When the quantity corresponding to HF - HK is minus, it must be set off below the line of no pressui'e.

The pipes leading from the ends of the cylinder to the indicator should DC large, short, of equal length, and as free from bends as possible ; otherwise, there will be loss of area in the diagram, and the apparent I.H.P. less than that really developed.

These pipes vary, in common practice, from |-inch to 1-inch diameter, according to their length and the piston speed, but are still, beyond doubt, the cause of very perceptible loss of area.

To make accurate tests of engines, to determine water consumption per I.H.P., &c., a separate indicator should be fitted direct to each end of each cylinder. This practice should always be adopted where any- thing like accuracy is required.

u

BNOINS POWER — ^HBAStJRBMBNT Of.

N.B. — ^The indicator shows only differences between the pressures of the steam and of the atmosphere, and not absolute pressures.

To ascertain the weig^nt of steam accounted for by ainr diagram, take a point A in the expansion curve of the diagi'am (fig. 8), just before release, and measure the absolute pressure there ; then take another point B in the compression curve, and measure the absolute pressure here also ; from Table CLXXIX. ascertain the weight of a cubic foot of steam at each of the pressures AZ and BZ.

Now calculate the volume, in cubic feet, swept by the piston while

Fig. 8.

travelling through the distance X, and multiply it by the weight per cubic foot at pressure AZ ; also calculate the volume corresponding to the travel Y, and multiply it by the weight per cubic foot at pressure BZ ; subtract the second product from the first, the remainder will be the number of pounds of steam accounted for by the diagram daring the stroke.

A similar calculation from the other diagram of the pair YfiM give the amount of steam accounted for during the return stroke, and the sum of the two — multiplied by the number of revolutions — the amount per minute or per hour.

The clearances need not be considered in these calculations if the

ENGINE POWER — ^MBAStTRBMBNT OF. 16

points A and B be taken at the same distance above the zero line of pressure.

This method is mainly usefal in determining condensation and re- evaporation that occur during passage of steam through a series of cylinders. No conclusion as to economy can be derived from diagrams only. They tell nothing about water that may be present in cylinders. Feed water must be measured to determine real economy of engine.

Shaft Horse-power is that transmitted by a shaft, and can be calculated from the torque as follows : —

T is the twisting moment or torque in inch-pounds. - R, the revolutions made per minute by the shaft.

2ir X T

The work performed per revolutions — -— or 0 6236 T.

Rule 14. 8.H.P. =2i2|«TxR^ TxE

^ 33,000 63,000

The torque on any shaft can be calculated from the angle of twist or torsion by means of the following formulae : —

a is the arc at a radius r of the angle of torsion 0, - =/3 ; 2 is the

r

length and d the diameter of shaft under observation.

^ 10-2xTxZ ,D T \

360 2irr ^^ 2ir* That IS i8= ^^^ = -;— -.

Then

360 57-3

$ ^10-2xTxg 57-3" Mrxrf* *

or (i) e = ^-t^'^^^J for solid shafts, Mr X d*

/••x ^__ 684 T X Z for hollow shafts when dj is the "" M.r{d^ - di^) diameter of the bore.

Thatis rj^^exd^xJJLr

684 x;

Mr is the modulus of stiffness or rigidity of the material, which for steel generally is 10 to 12 millions. With steel shafts of best make, experiments have shown the value of Mr to be 11,750,000 for solid, and

16 feNGINiB POWER — MBASUftBMEi^t OP.

12,150,000 for hollow. In everyday practice, 11,250,000 is taken fof solid steel shafts : —

then r^ J xd*x 11,250,000 ^^ej<d^^

584 z ;

Substituting this value of T in the formula for S.H.P.

Rule IS S. H. P. = 1 9, 264 ?^ x ^ -^ = ^l^ solid shafts. ^ I 63,000 3-27 x;

Rule isa. S. H. P. = ^(^* -/i*)R for hollow shafts. ^ 3-27 X I

Torsion Meters are the instruments employed to indicate the angular displacement of a definite length of shaft (usually 40 inches), when the shaft is receiving and transmitting power. They are all designed on the same fundamental principle, and consist of two cast- iron sleeves made in halves so as to go on the shaft, and be keyed to it a definite distance apart ; one is short and the other long ; each has a disc of considerable diameter at the ends adjoining, so that as the shaft twists the discs' edges are displaced with respect to one another by the amount a, which may be used instead of 0**, if desired, for calculating S.H.P. thus :—

RuleiSb. S.H.P.=2Il2iillRiii!.

rxl

There are many forms of torsion meter which may be classed by the methods adopted for indicating 0 or 3 : —

(i) Those having differential levers whereby the distortion is magnified, such as Professor Fottinger's.

(ii) Those which accomplish the same end by wheel and pinion gearing, as in the Denny- Edgecombe machine.

(ill) Those without sleeves, but with counter shafts coupled at their extreme ends to the shaft by driving gear and to one another by screw and nut, which cause longitudinal displacement, which is magnified by a lever ; as in the Collie meter.

(iv) Those which magnify the arc of the angle of torque by means of a beam of light reflected from a mirror, which is twisted through angle 9 ; as in the Hopkinson-Thring instrument, which entails the use of the least amount of gearing.

(v) Others, as the Bevis-Gibson, where a beam of light is made to pass through slits in discs at a considerable distance apart ; which becomes blinded on angular distortion taking place, and visible again after an angular movement of the sighting hole corresponding to 6, The registering is made mechanically and automatically by the Fiittinyer on a sheet of paper secured on a fixed drum surrounding the

BFFICIBNOY OF MAHIKIB MAOHINBBT. 17

shaft, so thai the magnitude of the angle or arc can be measured at any point by the distance from the base line made when the shaft is trans- mitting no power.

The Denny- Edgecombe machine shows the distortion on a dial which, however, is in motion on the shaft, but by a most ingenious electrical arrangement its indications are given on another dial fixed in any convenient part of the ship. It can be and often is made to auto- matically register its indications on a diagram, which show us the vagaries in torque of a reciprocator, or the mean torque of it or of a turbine.

The BxfpHrison'Thring wxnoxB throw a point or line of light on a fixed scale, from which at any time the angle may be read off ; it also registers its own zero line continuously, and by an arrangement can indicate the variations in torque of a reciprocator.

The Bevw- Gibson measures the torque by the amount of displace- ment required in the registering apparatus to bring the light holes in line.

A simple formula for each ship can be made and used for S.H.P. by simply multiplying it by 6 and revolutions ; in fact, a table may be made by including the revolutions, so that from it a co- efficient may bo taken and multiplied by 6 only. Thus if I is 40 and the diameter of the shaft 12 ins., then

Rulei6. S.H.P. =168-5 dxR.

And if at 400 revolutions e is 0-166', S.H.P. =10,461.

EFFICIENCY OF MARINE MACHINERY.

Efflciency is expressed by the fraction of the whole work or energy generated or supplied that is usefully employed for the purpose for which it was designed. Hence,

Efficiency of the boiler is the available heat transmitted to the engine as a fraction of that given out by the fuel.

Effijdency of the steam is the fraction of the total heat of evaporation that is capable of being converted into work.

The thermal efficiericy of an engine is expressed by the fraction of the work capable of being done by the steam or gas that actually is done by it.

The m^hanical efficiency is the fraction of the work developed in the generator that is actually passed on from it for external con- sumption.

The general effi/deney of a steam or gas engine is the fraction that the output of energy is of that available from the fuel.

Propeller efficiency is the fraction of the power delivered to it that is devoted to thrust power.

Propulsive effi^-iency is the relation of the nett or tow-rope H.P. to the gross H.P. developed in the propelling engines ; strictly speaking, it should be taken to the H.P. delivered to the propeller shafting, which can now be ascertained by torsion meters.

18

BFFIOIBNOT OF MABIKB MAOHINBBT.

BoUer efficiency is measured by taking the number of pounds of steam actually evaporated as the numerator and the thermal value of the fuel divided by the total heat of evaporation under the same conditions as denominator. For example, the average thermal value of the ordinary good Welsh steam coal is 15,600 B. T.Xf. The total heat of evaporation from 110** and at 841° (120 lbs. pressure abs.) is 1108 B.T.U.; then

greatest possible evaporation = ^^^ = 14 lbs.

A boiler using this fuel evaporates 10*8 lbs. of steam per lb. of fuel.

The efficiency =iiLr or 0-736.

14

Efficiency of steam by Rankine's formula is as follows : —

•n effective mean pressure in cylinders

mean pressure + rate of expansion x pr"^^/^ ,'

Themval efficiency is expressed, then, where Ti is the absolute tempera- ture at entry and T^ that at exit or exhaust.

Rule 17.

T — T Then thermal efficiency =—1= — ?.

Ti

For example, an engine works with steam at 180 lbs. pressure abs. at the H. P. valve and rejects into a condenser with a vacuum of 28 ins. Here Tj = 373° + 461° = 834°. T,= 90° + 461° = 651°.

Thermal efficiency = ^^^ " ^^^ =0-816.

834

The Maximuth Thermal EfEciency of any Condensing^ Steam Engine with a Temperature of 60° F. m the Condenser.

Working press. \ abB. /

40 0-284

80 0*326

100 0-839

120 0 850

140 0360

160 0368

180 0-876

200 0-381

220 0-887

240 0-893

260 0-898

280 0-404

Effloiency .

Ths mechanical efficiency of engines generally is ascertained by comparing the output H.P. as measured by a brake or other mechanical means. This is not possible with engines of great power. Since the introduction of the turbine as a marine motor, the torsion meter has been invented and used to indicate S.H.P. in reciprocators. Before this experiments had been made to ascertain the friction H.P. by running engines without their propellers at various rates of revolution and deducting it from the I. H.P. at the corresponding revolutions coupled up. The following has been ascertained by one or other of these methods : —

BFFIOIBNGY OF MARINE MAGHINEBT. 19

Rule i8. Mechanical efficiency = -^ — ' ' ' — '—^ .

1. H . r .

S H P Large qnadruple engines by Denny Bros., efficiency f~^~p' =92 to

94 per cent. Triple compound engines 900 I. H. P. by Central Marine Eng. Co.,

1*H.P» — F.H.P. fvr «« ^^^4.

== 96 per cent.

1. H. P.

Several large engines (triples) made in Germany showed an efficiency

from 88-5 per cent, to 93*5 in the largest (4500 I.H.P.).

Triple compound engines, 300 I.H.P., by Earles S. & E. Co. showed

84 '9 per cent., and similar engines 480 I.H.P. 90*2.

Compound engines of a torpedo boat by Mr A. F. Yarrow, 265 I.H.P.,

showed by dynamometric trials 92*3 per cent., and as much as 76 '6

per cent, when developing only 38*6 I.H.P.

Triple compound engines with /ore^ Ivbricaiion by Belliss k Morcom

gave by electric output and brake trials 93*16 per cent, at 429

I.H.P., and as much as 98*8 per cent at 218 I H. P.

Marine engine losses vary very nearly with the revolutions but the

power as the cube, the efficiency at low speeds is then less than at high

ones with the same engine ; further, the efficiency of small engines,

running on similar conditions as to pressure, rates of expansion, etc. , as

large ones, is lower. On the other hand, the smaller the engine is for

the power to be developed the higher will be its efficiency mechanically.

Qmeral efficiency of steam engines is gauged by the water or steam

consumption per I.H.P. The following schedule gives the greatest

possible output of work by a pound of steam under various conditions,

and the corresponding horse-power: —

If a steam engine consumes x lbs. of steam per H.P. hour, or — per H.P. minute, then a; =60 1.H.P., or, 1 lb. produces — I.H.P.

X

If X is the greatest possible output under similar conditions.

AO AO

Rule 19. General efficiency of engines = -— -^ X or ^=-.

X Xx

C^eneral efficiency of <dl engines must, however, be commercially dealt with differently, as fuel is the serious factor in any installation and must form the basis of comparison of a steam with an internal combustion engine. In this case the thermal value of a H.P. is 88,000-f 778 or 42*4 B.T.U. The value per hour is 2544 B.T.TJ. The

Welsh coal, with its calorific value of 16,500 B.T.U., is equal to 1M22

2644

or 6*10 H.P.

If an engine uses 1*3 lbs. per I.H.P. hour,

its efficiency will be i-— = 0*126 or only 12*6 per cent.

^ 6*1x1*3

20

BFFIOIBNOT OF MARINE MACHINKRT.

The oil engine using 0*45 lb. of fuel, whose calorific value is 18,800 B.T.U., will have an efficiency as ascertained in the same way —

l4.^A?22 X 0-46 = 0-30 or 30 per cent.

Rule 20. General efficiency of machinery installations = 2544-rB.T.U. value of fuel x weight consumed per H.P. hour.

From observations made at the tests of electric generating engines it is found that at constant revolutions the power required to overcome the friction of the engine itself is the same whatever the load may be ; and with varying revolutions and varying loads the friction per revolution is nearly constant ; it is therefore probable that with marine engines total friction varies nearly directly as the revolutions.

Now, as the total L H. P. varies as the cube of the revolutions, it will be seen that the mechanical efficiency of a particular marine engine is at a maximum at full speed.

rroude's Method.— As there is considerable difficulty in experi- mentally determining the power absorbed in overcoming the friction of a marine engine, the following graphic method is of interest : —

Knots

Fig. 4. A series of progressive trials having been carried out, and the resultb

BFFIOIBNGY OF MARINE MACHINBRT. 21

carefully recorded — calculate the indicated thrasts (from the formula — Indicated thrust =LMi^J^^i^, where P is pitch of propeller in feet,

and R revolutions per minute) for each speed, and set them up as< ordinates from a base line on which the speeds are set off — as shown in fig. 4. Then, supposing A to be the lowest known point on the curve, draw the tangent KA ; divide BC at D so that BO =1*87 DC, and through D draw the vertical line D£, cutting the tangent in F ; and through F draw HG parallel to the base line. The neight OH then represents the constant friction of the engine, and the point H is the vertex of the thrust curve which may now be completed.

The lengths of the ordinates intercepted between HG and the thrust curve represent power expended in overcoming ship's nett resistance, augment of resistance due to propeller, and friction of propeller blades, and are proportional to the ship's resistance,

It is also very difficult to aetermine the frictional resistance of any pair of parts of an engine, owing to the difficulty of reproducing exact conditions of actual work in an experimental apparatus, so here again values can only be estimated from those obtained by experiments made under conditions approximating to those of an actual engine.

The experiments of Tower (made for the Institution of Mechanical Engineers, 1883-91) and of Dewrance (1896) are instructive, as the results obtained were most important ; but their tests were all made on journals under constant load, and therefore under very different conditions to those prevailing in the crank bearings of recipiocating engines, and experience has shown the latter to be capable of carrying much greater pressures than bearings subject to constant load.

Tower and I)ewrance's experiments may be summarised as follows : —

1. When a bearing is running satisfactorily the surfaces are not in metallic contact, but are separated by a film of oil.

2. Actual measurement by pressure gauges showed that near centre of brass oil was under a pressure somewhat greater than mean pressure per square inch (i,e, total load-rdia. x length of journal) carried by bearing at the time, and that pressure decreased as ends and sides of bearing surface were approached, and became zero at edges.

3. The drilling of an oil hole at centre of crown of brass allowed oil to be forced out, caused pressure to fall, and diminished load that bearing could carry. These results made it clear that oil should be introduced to bearings of this type where pressure is least, and that no openings should be made near centre of bearing surface, where pressure is greatest. It was found necessary to lubricate experimental journal by means of an oil bath, because, when oil holes in top of brass were used, results were very irregular and frictional resistance was about four times that registered when oil bath was in use.

4. So long as lubrication remained efficient the frictional resistance under varying loads remained constant^ i e. was unaffected by pressure per square inch to which bearing was loaded.

6. The frictional resistance varied very nearly as the square root o* the nibbing velocity.

22 ■FFICIKNCT OF MARINS MAGHINSRT.

6. The temperature at which the bearing was nm was found to be most important, one expenment, made with lad oU under a proesure of 100 lbs. per square inch, showing that the frictional resistance was three times greater at 60* than at 120^ Apparently there is a most suitable temperatore for each lubricant at each pressure.

For a temperature of 90* the aboTe results are yeiy accurately expressed by the formula —

F=20Cx\^ ^^

where F= friction factor or co-efficient, y= rubbing Telocity in ft. permin., P=nominal pressure in lbs. per sq. in., C=*0014 for sperm oil, '0015 for rape, '0018 for mineral, and '0019 for olive oiL P had a range of about 100 to 500 lbs. per square inch.

Frictional resistance depenas on — (a) Velocity of rubbing ; (b) in- tensity of pressure ; (c) temperature ; {d) lubricant ; («) nature of rubbing, i,e. continuous or constantly reversed ; (/) form of surface, i.e. curved, like a bearing, or flat ; {g) material and condition of sur- face ; {h) extent of contact, i.e, all over a surface, or only on a line ; (j) method of application of lubricant.

As regards Q), Dewrance*s experiments appear to show that the composition of the alloys used had, other tlungs being. equal, little or no effect on results obtained, — a result difficult to reconcile with common experience to the contrary with ordinary engine bearings.

As regards (h), reduction in surface appears to reduce frictional resistance (as in the case of a railway carriage wheel when *' skidded "), so that surfaces should not greatly exceed those found to give reason- able length of life under usual conditions.

Dewrance found {j) most important, and by carefhl arrangements succeeded in caiTying loads of well over one ton per square inch, whereas with defective (but very usual) arrangements Uie same bearing would not carry one-tenth of that load. He found it necessary to ease away the brasses at the sides in a very gradual manner and to admit the oil at the 8id&s, or points of least pressure, whence it was carried forward by the revolving journal into the gradually narrowing clearance spaces and towards the points of greatest pressure.

Any sudden contraction of this clearance space, or any ridge tending to scrape the oil from the surface of the journal, was found to lower seriously the load-carrying power of the bearing.

The fact that a crosshead shoe will not usually work satisfactorily with a load of more than about 50 lbs. per square inch, whilst a bear- ing can easily be made to carry ten times as much, still waits- an explanation. Difficulty of lubrication, and the continual reversal of the motion, will no doubt partly explain the anomaly ; but, even if all the rubbing surfaces about an engine were of equal smoothness, worked at same temperature, with same lubricant, and at same speed of rubbing, it would still be almost impossible to fix the various values of the friction factor. And as to frictional losses caused by

BFFIGISNCY OF MARINE MAGHINERT. 23

tightness of piston rings, and of gland packings, and by screwine up of bearings, — they may be anything, and cannot even be estimated.

The ^ciency of the same engine may therefore vary greatly at different times, and the frictional resistance of a bearing (say) may be almost anything between that due to the friction of solid on solid and that due to liquid friction. The laws governing the Mction of solids are as follows : —

(a) The frictional resistance varies directly as the load.

{b) It is independent of the extent of surface in contact.

(c) It tends to diminish with an increase of velocity above a certain limit.

THE THERMAL AND POWER VALUE OF A POUND

OF STEAM.

Maximnm Output from i lb. of Steam in B.T.U. ^ and Horse-power.

The following Tables — V., VI., and VII.— give the amount of work that is theoretically possible under the different conditious stated. Table VII. is a general one giving the output when steam is expanded from an actual pressure Piio & pressure P2, at which it discharges ; this is the case of a turbine during its various stages and throughout Table V. gives the output when steam is expanded from a pressure Pi^ expands to a pressure p^t and then exhausts to a condenser in which the pressure is one pound — that is, the vacuum is 28 inches, which is the case of the ordinary reciprocating condensing engine. Table VI. eives the output when exhausting to the atmosphere, as in the case of locomotiyes and other engines which have no condenser. It will be seen that a turbine supplied with steam at 100 lbs. pressure (absolute) can do the same work as a triple compound reciprocator expanding steam of 160 lbs. to 5 lbs. , or one of 200 lbs. expanding to 7 lbs. And a locomotive would require 55 per cent, more steam at 200 lbs. pressure to do the same work, supposing the efficiency of the means is the same in each case. It will also be seen that steam at 100 lbs. has a 19 per cent higher potential than that of 50 lbs ; that 150 is 8*44 per cent, higher than 100 ; that 200 is 5*77 per cent, higher than 150 ; and 250 is 4*82 percent, higher than 200. Also that the 260 lbs. of the new quadruple has a potential 7*41 per cent greater than the 176 lbs. of the older triples.

24

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RESISTANCE AND PROPULSION OP SHIPS. 27

EfiSciency as afifected by Jacketing^.

Car^fal investigations show that all types of steam engines are rendered more efficient by the addition of steam jackets, and that the more completely the hot surfaces of cylinders, receivers, ko., are jacketed, the greater is the saving effected.

This amounts to saying, that for every pound of steam condensed in the jackets, some greater quantity is saved in the cylinders. The ratio of steam saved in the cylinders to steam expended in the jackets, varies from a little under 2 to 1 in some types of engine, to over 5 to 1 in other types.

The gain that may be expected to result firom jacketing an engine depends on such a multitude of considerations — relating not only to the design of the engine and of the boiler, but also to the management of the machinery under steam — that it can only be very generally stated as lying between 5 and 25 per cent, of the total feed-water evaporated ; but in the case of moaem marine machinery, of good construction, it is not probable that the gain is over 10 per cent.

The limit of usefulness of jacketing is reached when the exhaust is just free from particles of water in suspension.

Small cylinders are more benefited by jacketing than large ones, in consequence of the ratio of area of hot surface to cubic contents being greater than in large ones ; and slow moving engines benefit more than quick.

It is important that there should be a thorough circulation of steam in the jackets, but the plan of passing the steam through the jackets on its way to the H. P. cylinder should be avoided.

THE RESISTANCE AND PROPULSION OF SHIPS.

In dealing with cubes, or with parallelepipeds of similar form, immersed in water until the uppermost face is just fiush with the surface, it ia found, on making the necessary calculations, that the wetted surface is exactly proportional to the §rd power (or the square of the cube root) of the displacement. Taking the case of cubes, —

Let L = length of edge, D = displacement, W = wetted surface ;

thenD = L», orL=^D,

and W = 5 X La= 6 X (->yD)». That is, W varies as D§.

It may also be noted that U={*^Dff—th&t is, L^ (jvhich corresponds to mid-ship section) also varies as DJ ; and therefore W varies as L^, or, in other words, wetted surface varies as area of mid-ship section.

These results are not quite accurate for parallelepipeds which are not similar in form (that is, whose lengths, breadths, and depths are not of the same relative proportions), but the inaccuracy is only slight within practicable limits ; so that, if ships of ordinary proportions ar*-

28 RESISTANCE AND PROPULSION OF SHIPS.

substituted for cubes or parallelepipeds, it is practically correct to say that wetted surface varies as area of mid-ship section, and also us |rd power of displacement

For similar vessels displacement is also a measure of the fineness of the lines, since, when length and mid-ship section are the same, it varies directly as the prismatic co-efficient of fineness.

Now the resistances of ships depend almost entirely upon these two elements, — wetted surface, and form, or fineness of lines, and may be classed under the four heads —

(1) Resistance due to skin friction ;

(2) Resistance due to eddy making ; (8) Resistance due to wave making ;

(4) Resistance (augmented) due to the action of the propeller on the ship.

The first of these depends on' the extent and nature of the wetted surface, and the depth of immersion ; the third, on the lines of the ship, and on her degree of fineness ; and the second, on all of these combined. The fourth arises from the displacement of the water and the consequent reduction of "head" and pressure on the stern. Propellers of large diameter and fine pitch produce much augmented resistance as well as negative slip due to the big toake atrrettts.

Residual Resistance— that is, the resistance from all other causes than skin friction can be estimated with a fair degree of accuracy by the following formula of Mr. D. W. Taylor, U.S.A. :—

Rule 21. Residual resistance in lbs. = ^-

h is the hhck co-efficient ; D, the displacement in tons ; Y, the speed in knots ; L, the length on waterline in feet.

This formula is applicable only to speeds for which -=~ is less than 1 '2.

For merchant ships, with block co-efficients 0*6 to 0*6.5, this is a

ya good formula for speeds, such that -=7- = 0*85 ; when co-efficients are 0'5

to 0*55, then — = \,

Li

It is therefore evident, from the above considerations, that the old s{)eed and power formulae rest on a sound basis, and are capable, in careful hands, of giving fairly accurate results. These formuls are : —

Rule 22. I.H.P.=?il®!

d I H P _ftr^ Q^ immersed mid-ship section x S^

Ix.

where D, is displacement in tons ; S, speed in knots ; and 0 and K co-efficients.

The peculiar value of these formulse lies in the fact that they cnn be applied at a very early stage of the work, before such data as angles of

RI8I8TANGS AND PROPULSION OF SHIPS. 29

• obliquity of stream lines can be obtained with any degree of accuracy : and thus the power, approximate weight, and an outline drawing of the machinery can be got out simultaneously with the design of the vessel, — a great adrantage where time is limited, as is usually the case in preparing tenders.

It is important to notice, in connection with the above formulae, that — although the resistance of a ship, moving uniformly at any speed, may vary as the square of that speed, — the power required to over- come the resistance, and propel it at any speed, varies as the cube of that speed. For, —

Let S= speed in feet per minute ;

R= resistance in pounds at that speed ; Then R=S^ x C,— where C is a co-efficient ; and, multiplying both sides by S

RxS = S»xO.

But R X S is the work done, in foot-pounds per minute, in overcoming the resistance R through the space S, and, divided by 83,000, is equal to the nett horse-power required to drive the ship. This law only holds for similar ships driven at corresponding speeds (speeds pro- portional to the square roots of the linear dimensions), since it is evident that the resistance due to wave making can only be proportional under these conditions.

The second formula is useful as a check, or corrective to the first, where the vessels under consideration are not absolutely similar, but have same ratio of length to breadth and draught, with a variation in the rise of floor.

Table VIII. (given by Sir W. H. White) shows the values of 0 for some typical ships of very different classes, at various speeds, and whilst indicating generally the range of tho variations that occur, serves also to show the difficulties that the naval architect has to encounter in obtaining high speeds in vessels of small dimensions.

It is, perhaps, scarcely necessary to add that these co-efficients of performance represent the combined efficiency of ships and machinery, and that they are therefore just as liable to be effected by an un- suitable propeller as by a foul bottom or unsuitable lines ; and also that for every model there is, as a rule, only one speed of maximum efficiency, though it is evident from the type of curve usually obtained, that there may be two speeds at which the efficiency is equal and slightly below the maximum.

It should also be borne in mind that accurately determined co- efficients of performance, &c. , generally apply to more or less smooth- water conditions, and that a form of vessel which gives highest speed with least power, on such trials, may be far from the best for an ocean- going steamer.

As a rule, length assists speed especially in a sea-way.

The gain vA economy of propulsion resulting from increase in dinaen- sions is made very clear by the following figures, which are derived from the trials of certain cruisers : —

30

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RESISTANCE AND PROPULSION O* SHIPS.

31

Table Villa.— Relation of Powers and Dtsplacements.*

Length in ft. . '

Bi-efiulth in ft. Mean draught in ft Displacement in tons l.H.P. for 20 knots I.H.P. per ton of dis placement .

No.1.

No.«.

NaS.

No. 4.

No. 6.

280

800

860

435

500

85

43

60

69

71

13

16^

28i

24i

26i

1800

3400

7400

11000

14200

6000

9000

11000

14000

15500

8-8

2-65

148

1-27

109

The following horse -powers were required to drive cruisers Nos. 4 and 6 in the atNOve Table at the speeds named :—

No. 4.

No. 6.

10 knots

1500 I.H.P.

1800 I.H.P.

12 „

2500 „

8100 „

14 „

4000 „

5000 „

16 „

6000 „

7500 „

18 „

9000 „

11000 „

20 „

14000 „

15600 „

22 „

23000 M

23000 „

The frictional resistance of clean painted surfaces varies about as the 1*83 power of the speed (compare Table XVI.), but resistance due to wave making may vary very widely, since it is dependent on form. The total resistance of " Destroyers " has been found to vary as follows * :— ^

Up to 11 knots,

. • . nearly as speed '

At 16 „

• . . , , speed •

,,18-20 „

„ speed «;»

„ 22 „

,, speed

,s 2o „ •

,, speed •

,, 26-80 ,,

practically as speed '*'»

aud the resistances other than frictional vary as follows : —

Up to 11 knots as speed ' At 12^ to 13 knots ,, speed ' f, 14 J knots ,, speed *

18 „ , , speed ^^^ ^*^^ ^^ vowv^.

24

,9

,1

f I

and at higher speeds as still lower powers of the speeds.

• Sir Wm. White, British AMOciatlon Address. 18M.

32

RHSISTANCIB AND PROPULSION OF SHIPS.

The relation of the frictional resistance to the total resistanoe at Tarious speeds is computed to be as follows* : —

"Destroyer." • Cruiser.

At 12 knots 80 per cent. 90 per cent

„ 16 ,, 70 „ 85

„ 20 ,, noarly 50 ,, nearly 80

>i 23 ,, ... over 70 M 30 ., 45

*>

And it may be remarked that, if the coefficient of friction be doubled (as Table XVI. shows it might easily be with a foul bottom) the maximum speed of the *' Destroyer" would fall fully 5 knots, and that of the cruiser would be reduced from 23 knots to 19.

Recent * * Destroyers " for ahe British Navy have been of following dimensions, etc. : —

Ft. long.

Tons displ.

I.H.P.

Knots.

1898

180

240

4000

26-27

1896

200-210

280- 300

5500-6000

80

1899

230

360- 380

8000-10,000

32-33

1903

225-230

550- 590

7000

25-5

1907

250-270

860- 960

14,000

33

1910

270-280

900-1000

12,000-16,000

27-33-5

The propelling apparatus of these boats has given, on an average, 46 I.H.P. per ton of weight. In the 30 knot boats nearly 50 per cent of the displacement has been allotted to the propelling apparatus, and the load of fuel and equipment has taken 12 to 14 per cent. more.

* Sir Wm. White, British AssociatioD Address, 1899.

RBSISTANCB AND PROPULSION OF SUlPS.

33

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34

RESISTANCE AND PROPULSION OF SHIPS.

Table X.— Results of Trials of

Particulars.

Length, perpdlra, ft, Breadth, extreme, ft., Drft water, mean, ft. , DUplacement (tons), Imrsd mid sectn, sq.ft. Wetted skin, sq. ft.. Prism co-efficient, . 0-4VL-S-V8., . Speed (knots), . Number of screws, . Engines, .

I.H.P. or S.H.P.,

H.P. per 100 sq. ft. wetted skin. Do. reded to 10 kns.

D|xS8+H.P. . .

H.P.-i-DlBpmt} .

Service of ship, .

QS3 LCNA

TSS KWO

760

678

87-6

72-0

32-5

29-6

86,440

26,500

2,600

1,960

82,850

65,160

0-671

0-713

0-714

0-712

25*40

23-50

4

2

Turbs

Recip

64,600

39,000

78-4

59-90

4-7

4-62

278

297

68-7

48-7

Atl Ex

Atl Ex

TSS OCNC

TSS DLD

I'ss ;

CPA

686

668

600

68-0

67-0

66-2

29-9

29-0

29-0

25,910

23,620

21,600

1,922

1,768

1,720

67,209

62,110

54,780

0*690

0-716

0-729

0-725

0701

0-704

20-80

28 60

22*09

2

2

2

Recip

Recip

Recip

26,600

36,000

29,936

89-4

57-9

64*8

4-88

4*47

5-08

297

297

278

80*2

44*9

88-8

Atl Ex

Atl Ex

Atl Ex

TSS

678

72-4

80-0

27,500

2,064

68,700

0-679

0-748

20-19

8 Turbs

24,000

86-00

4-26

312

26*8

Atl Ex

HMS INBL

580

78*5

26-0

17,250

1,868

47,340

0660

0-687

27-36

4

HMS HMS DNT GLS

490

82-0

26*6

17,900

1,912

44,630

0-669

0*680

21-25

4

Turbs Turbs

47,800

100-0

4*88

289

70-8

Cruiser

24,712

56*4

6-78

264

86-1

Bttlsp

430 47-0 16-25 4,800 624 22,250 0 625 0*613 26*80

4 TurbB

26,417

114

6-27

203

89*2

Cruiser

RKSI8TAN0B AND PROPULSION OP SHIPS.

35

Various Ships of High Speed.

HMS BLN

886

41- 5

13-6

8,860

476

18,100

0-640

0*586

27-8

4 Turbs

18,000

99*4

4-63

267

80-4

CrniBer

HMS

SFT

846 34*2

10-6 1,800 301 12,000 0-609 0*624 36-00

4 Turbs

80,000 260 6*36 230 203

TSS BMC

876

46-0

18*4

8,863

690

18,830

0 630

0-617

28-27

8 Turba

14,700 78-1 6-17 192 66 6

HMS SKR

Scoat Home

360

40 0

14*26

2,946

600

16,360

0*572

0-694

25-20

2 Hecip

16,899

103-4

6-46

202

82-2

Scout

PSS EMQ

PSS LMG

TSS QN

TSS PG

360

330

310

290

42-3

40-0

40-0

88-0

130

8-75

10*5

11-92

2,940

1,868

2,080

2,100

466

322

375

416

16,190

13,082

12,200

13,170

0-623

0-615

0-625

0-609

0*620

0-604

0-602

0-605

21-71

22-8

21-73

20-34

Paddle

Paddle

3

2

3Cyl Oomp

Diag Oomp

Turbs

4 Ok Trpl

11,442

7,500

8,000

5,820

70-6

57-3

65-6

44-2

6*96

5-16

6-19

6-27

183

223

210

236

55-8

49-3

49*1

■ ■

Home Ex

Home Ex

Home Ex

Open SEx

TSS SNA

TSS NRMA

284

290

39-0

36-0

12-0

12-0

1,990

1,875

420

390

11,960

11,700

0*554

0-680

PSS LND

PSS RS

0-608 20-00

8 Turbs

6,670

56-8

6*97

190

42-2

Home Ex

9-612

19-70

2

Geared Turbs

5,000

42-8

5-60

232

32-9

Home Ex

838

34*75

9-00

1,700

292

11,800

0-607

0-617

21-50

Paddle

Oomp

7,000 50-3 6*97 202 49-3 Ch'nn'l

310 330

6-0 1,063

188

9,920

0-635

0-623

19-6

Pdle

Diag Oomp

3,500

35-3

4-60

223

33-6

Home Ex

36

RBSISTANCE AIH) PROPULSION OP SHIPS.

Kirk's Analysis.

The following very simple and useful method of estimating. wetted skin and comparing forms of ships is generally known as ** Kirk's analysis *' : —

A diagram, resembling fig. 6, called the "block model" is first made, the dimensions being determined as follows : —

Length AB = length of ship (from forward side of stem to after side

of stern-post, at mean trial draught).

Depth KL = depth of ship from mean trial draught to top of keel

(if any).

Fia. 6.

Breadth EK — -^^ea of immersed mid -ship section

IvLi

. TT _ n p _ Displacement in tons x 35*

• Area of immersed mid-ship section '

Length of A D = VAG^ + GD^.

Then, the wetted surface of the ** block model " is, — (EK X AH)-|-(2KL x FK) + (4KL x AD).

The angle of entrance is EBK ; EBH is half that angle ; and tan.

EH EBH = =5^ ; or, the tangent of half the angle of entrance is equal to HB

Half breadth of model^ ^^^ ^^^^ ^j^.^^ ^ ^^^^ ^^ ^ ^^^^ ^^ ^^^^^j Length of fore-body

tangents, the angle of entrance may be obtained.

* 35 cubic feet of salt water weigh one toD, and are therefore equal to one ton displacement.

RBSI8TANCE AND PROPULSION OP SHIPS.

37

Table XI.— Angles of Entrance, given in degrees, suitable for

various Speeds and Lengths.

t - ■

«'2

Speeds of Ship in Knots.

1®

10

11

12

18

14

15

16

17

18

19

20

21

22

28

24

26

feet 200

26-3

23-9

21-9

201

18-8

17-6

16-5

15-5

14*6

13*9

18*2

12*5

12*0

11*4

11*0

10*6

250

27-8

26-3

23-2

21-4

19-9

18-6

17-4

16-4

16 -6

14*6

13*9

13*3

12*7

121

11*6

111

800

291

26-6

24-3

22-4

20-8

19-4

18-2

171

16*2

16*8

14*6

13-9

13-2

12*7

12-1

11-7

Z50

30-3

27-5

25-2

23-3

21-6

20-2

18 9

17-8

16*8

15*9

161

14*4

13*8

13-2

12*6

12-1

400

81-3

28-5

26-1

241

22-4

20-9

19-6

18-4

17*4

16*5

16*7

15 0

14-2

13-6

13-1

12*5

450

82-2

29-3

26-9

24-8

28-2

21-6

20-2

190

17*9

170

16*1

16-4

14*7

14*0

13-4

12-9

600

331

301

27-6

25-5

23-7

22-1

20-7

19-5

18*4

17*4

16*6

16*8

15*1

14*4

13-8

13*8

650

33-9

80-8

28-2

26-1

24-2

22-6

21-2

19-9

18*8

17*8

17*0

16*1

15*4

14*7

141

13*6

600

34-7

31-5

28-9

26-7

24*8

231

21-7

20*4

19*3

18*3

17-3

16*5

16*8

161

14*4

13*9

660

36*4

321

29-4

27-2

25-2

23-6

22-1

20*8

19*6

18-6

17*7

16*8

16*1

16-4

14*7

14*1

700

36-0

32-7

30-0

27-7

25-7

24-0

22-5

21*2

200

19 0

18*0

17*1

16*4

16*7

16*0

14-4

760

36-6

83-3

30-5

28-2

26-2

24-4

22-9

21-6

20-4

19*3

18*3

17*6

16*7

16-9

15*3

14*7

800

37*2

83-8

810

28*6

26-6

24-8

23-2

21-9

20*7

19*6

18*6

177

16-9

16*2

16*5

14*9

If ships are of very fine form for the speed required, and assuming that I.H.P. varies at S^ the power per 100 feet of wetted skin at 10 knots should be 4*0 I.H. P. ; on the other hand, if the ship is not sufficiently fine for her maximum speed, the efficiency will be much less and the power at 10 knots may be then 6*0, That i^, the power required to drive a ship of fairly good lines at a speed S knots is, —

Rule 22a. I.H.P. per 100 square feet W.S. _S»x4'6^g3 ^ Q.QQ^g

10*

Example : — ^To find the I.H.P. necessary to drive a ship at 16 knots, the wetted skin of ** block-model " being 16,200 square feet, the lines rather full.

The I.H.P. per 100 square feet = 15» x 0*005 = 16-875

and I.H.P. required =16 '87 5 x 162=2744.

In ordinary practice the wetted surface of the *' block model" is found to exceed that of the actual ship by 2 per cent, (in the case of full ships), by 8 to 5 per cent, for ordinary steamers, and as much as 8 per cent, in the case of very fine steamers.

The following Table gives, on inspection, the horse-powers required per 100 feet of wetted surface at various speeds and rates, aua will facilitate calculations by the above method : —

38

RESISTANCE AND PROPULSION OP SHIPS.

Table XII.— I. H. P. per loo feet of wetted surface at

different speeds.

Speeds

In Knott.

9 9- 10 lo- ll Il- ia 13 18 18- 14 U- 15

is- le

16-

17

17-

18

18-

19

19-

I.H.P. per 100 sq. feet of wetted nirfaee at 10 knoti.

4-3

10-9811 26 12 19 12-60 18-60:i8-84 14-89 15 -27 16-38 16-79 17-9718-42 19-65120-14 21-44 21-97 23-83123 '91 25-33 25-96 27-44 -28-12 29-66 80-40

806

8-60

4-30

4-86

6-69

6-89

7-26

8-20

9-28

10-88

11 62

13-80

14-17

15-64

17-20

18-87

4-8

814

8-68 4-80 4-98 6-72 6-64 7-43 8-40 9-45 10-58 11-80 18-11 14-61 16-01 17-61 19-81 20-63'21 12 31-62 22-61123-04 28-58 24-49 25-08 25-66 26-69'27 -22 27-86 28-8l'29-49 80-18 81-14 81-88 83-63

4-4

8-31

8-77

4-40

609

6-86

6-69

7-60

8-69

9-67

10-83

1307

18-41

14-86

16-88

18-03

19-76

4-6

8-38

8-86

4-60

6-31

6-99

6-84

7-78

8-79

9-89

1107

13-85

18-73

16-18

16-76

18-48

20-21

4-6

8-86

8-94

4-60

6-83

613

6-99

7-95

8-98

10-10

11-33

12-62

1402

15-62

17-18

18-84

20-66

2311 22-60 24-12i24-65 26-24126-88 38-49 29 12

4-7

8-43 4-03 4-70 6-44 6-36 7-16 8-12 9-18 10-83

4-8

8-49 4-11 4-80 6-66 6-89 7-80 8-39 9-87 10-64

11-5611-81 12-9013-17 14-8314-68

15-86 17-60 19-36 31-11 38 09 35-19

16-19 17-87 19-66 21-66 28-68 26-72

80*86 88-87

81-55 84-11

27-4127-99 29-76 80-89 82-92

'32-24 84-86

86-69

4-9

8-67

4-19

4-90

6-79

6-63

7-46

8-47

9'67

10-76

1306

18-44

14-94

16-68

18-25

20-07

22 01

24-07

26-26

28-68

8102

88-61

86-88

ft-0

• 1

8-64

4-38

600

6-79

6-66

7-t

8-64

9-76

10-98

12-30

18-75

16-34

16-87

18-63

30-48

32-46

34-56

26-80

2916

31-66

84-29

87-07

8-71

4-86

6-10

6-90

6-79

7-76

8-81

9-96

11-20

12-66

18-99

16-66

17 21

18-99

30-89

33-91

36-06

27-33

29-74

83-29

84-98

87-81

••S

'47S 446

6 30

6-03

6-93

7-91

899

10 16

1142

13-79

14-37

16*86

17-64

19-86

31-80

33-86

35-56

27-87

30-88

83-93

86*67

88*66

There are several simpler methods of estimating approximately the wetted skin, such as : —

Mumford Rule, which is more accurate than Kirk's, is as follows :—

Rule 23. —Wetted skin = (L x D x 1 -7) + (L x B x C)

or L(1-7D + B.C).

L is the length between perpendiculars ; D is mean draught ; and B the beam, all in feet ; G is a factor which is the block co-efficient ; that is,

p__ displacement in cubic feet " LxBxD

Seaton*s Rules are, —

(a) Rule 24. Wetted skin = {exdxL) +

Dx35 d

c= 2 area of immersed mid section -f B x (2. For shallow draught ships c=2. For ships with high rise of floor c= 1*6. For ordinary ships whose draught of water is not less than J the beam c=l'8.

D is the dispUcement in tons, d the mean moulded draught of water.

RBSISTANCB AND PROPULSION OF SHIPS. 39

(b) Rule 25. Wetted skin = i2\/K x D^

42VK = F; K=L-^(0•66B+d)

Where K is 4 the value of F is 69 '4.

5 ,, 62*9.

6 ,, 657. 8 „ 70-6.

It ^ »» 72'8,

10 ,, 74-7.

11 „ 76-4.

(c) Rule 26. — Suitable prism co-efiQcient for speed S, —

Pc=0-4Vl^-J-\/S.

{d) Rule 27. — Maximum economic speed for ship L feet long and prism co-efficient, F,—

S = (0-4VL-^Pc)«.

(0) Rule 28.— Minimum length L for a speed S with a co-efflcient prism F, —

H^f

Speed and Power Curves, etc.

The most reliable method of determining the I.H.P. required to drive any proposed vessel at a given speed is to base the calculations upon the results obtained from the trials of '^similar*' vessels; the basis of which is the fact that "similar" vessels, driven at ''corresponding" speeds, have the same co-efficient of performance, when the efficiency of the machinery is the same.

"Similar" vessels are those having the same ratio of length to breadth, and to draught, and the same degree of fineness ; and "corresponding" speeds are those which are proportional to the square roots of the linear dimensions of the respective vessels {e.g. proportional to the square root of the lengths).

Froude found that the resistance of such vessels varied almost exactly as wetted surface x (speed)^.

But to render the results of former trials readily accessible for such a purpose it is very desirable to have them plotted down as a series of curves, somewhat in the following maimer : —

40

RBSISTANCB AND PROPULSION OP SHIPS.

Speed in knots. Fig. 6.

B X C

Let Pi, Pg, Pg be the indicated horse-powers developed in obtaining the speeds S,, Sg, S3 knots, with Ri, R^, l^s revolutions per minute.

Take a line AN (Fig. 6) as a base line, and on it take points B, C, D, so that AB, AC, AD are proportional to S,, Sj, 83 ; at the points B, C, D erect ordinates B6, Cc, Dd proportional to Pj, P^, P3, and through the points 6, c, and d draw the curve d eb a, which is called the "curve of power" or "curve of I.H. P." The nature of this curve is then such that if an ordinate be drawn through any other point X in the line AN, Xx will represent the power necessary to obtain the speed AX from the same vessel, or another vessel of the same form and dimensions.

If the curve be accurately drawn, it will be found that it does not pass through A, but at a distance Aa above that point, thus signifying that a certain amount of power is developed even at zero speed ; Aa thus represents the power required to overcome the constant friction of the engines. (See also page 17, under "Efficiency of Marine Machinery ")

Similarly a curve of revolutions may be constructed by taking points Tit rg, r^ in the ordinates so that Br, O, Dr are proportional to

Ri. Rjj 1^8-

The slip may also be shown by a curve whose ordinates are propor- tional to the slips at the speeds S^, S^, S3.

Examination of the curves will show ;—

RESISTANCE AND PROPUI^ION OP SHIPS.

41

(1) The I.H.P., revolutions, and slip corresponding to any speed

intermediate to those observed ;

(2) The constant friction, and therefore general efficiency of the

engines ;

(3) The suitability of the lines of the ship for the speeds,— a

sudden rise of the curve towards the higher part, showing an undue increase of resistance at the higher speeds ;

(4) The power of the speed with which the I.H.P. increases for the

particular type of ship ;

(5) The suitability of the propeller to the ship, — any sudden rise

in the slip curve showing that the propeller is defective, either as regards diameter or surface, or both. Perhaps the most useful curve, however, for the purpose of deter- mining the power required to propel some "similar" ship, of different size, at any given speed, is one constructed as shown in fig. 7, where the abscissae represent speeds in knots, and the ordinates numerical co-efficients of performance, derived either from the Admiralty formula

( I.H.P, = — Y^ — ) ^^ other similar expression.

Rule 28a. — Suppose fig. 7 to represent the curve given by a vessel 250 feet long and 2400 tens displacement, and that it is required to determine the power necessary to drive a ** similar " vessel of 360 feet long and 7200 tons displacement at, say, 13 knots. The question then is, — what co-efficient of performance must be assumed? — ^and it is answered as follows : —

270

260

260

24-0

230

'Z20

2tO

42 BBSISTANCB AND PROPULSION OF SHIPS.

V360 : V260 : : 13 : aj

or a:— V^SO x 18 _ - Q.g _, J * * corresponding '* speed of V360 " ' first, or type ship,

and running up the ordinate for 10*8 knots until it cuts the curve, and then along the abscissa from this point of intersection the figure 253 is found, and this, when used in connection with the formula, gives 8250 as the required I.H.P.

In cases where there are no records of exactly " similar ** ships, the value of the estimate made will of course depend very largely on the experience of the estimator.

Determination by Model Experiments.

Another method, employed by the Admiralty, and many of our leading firms of shipbuilders, for determining the power required to propel any new type of vessel is, to ascertain the resistance of a model of the new vessel in the experimental tank, and to calculate the power from the results obtained ; and, where widely divergent types have to be dealt with, the method is no doubt of great value, but the expense is necessarily great.

The models arc usually made of paraffin wax, from 12 feet to 20 feet long, and from |-inch to 1^-inch thick ; they are cast nearly to shape, and trimmed to the exact form on a shaping machine. The speeds and tension on the tow-rope are automatically recorded on pa))er drums driven by clock-work. The height and position of the waves created, — which are of special importance in the case of paddle vessels, — can also be noted and recorded.

The horse-power required is calculated from the resistance of the model, by the same principle of ** corresponding*' speeds referred to above, as follows : —

Let I and L= lengths of model and vessel, respectively ; V and V= corresponding speeds ; r and R= corresponding resistances ;

Then- =

-= /-

and ^*' '

Example. — Suppose the E.H.P. nett or efi'ective horse- power necessary to drive a ship 800 feet long at 15 knots is required. Let the length of the model oe 12 feet, then the "corresponding" speed for it will be given by, —

= 16 >.. /J^ = 3 knots. V 300

RB8ISTANCB AND PROPULSION OP SHIPS. 43

Assume the resistance of the model at this speed to be 4 lbs., then resistance of ship at 15 knots will be, —

R=4x^^y=62,6001b8. ;

^62,500 X 16 x6080^ggy 60x88,000

or E.H.P. required is approximately 2879, — a slight con-ection having to be made for skin friction.

Co-efiBcients of Fineness.

The block eo efficient expresses the ratio borne by the displacement volume to that of the parallelepiped circumscribing the immersed body.

Let V= displacement in cubic feet ; L= length on water line ; B = OTeatest immersed breadth ; D = draught of water of body {ex keel) ; K = displacement co-efficient.

Then K=— -^-— . LxBxD

Th>e prisnuUic eo-efficient; — which gives a truer measure of fineness of Unes iSian the above, — expresses the ratio borne by the displacement volume to that of the prism swept by moving the immersed mid -ship section through the length at load water-line.

Generally speaking, the finer the water lines are, the easier is the ship driven at any speed, and consequently the speed co-efficients or multipliers vary inversely with the co-efficient of displacement. But as there is a limit to the speed at which a certain ship may be driven, any increase in power produces little or no increase in speed ; there is a limit to the fineness for the lower speeds also, so that any decrease in the co-efficient of displacement causes little or no increase in the speed co-efficients — in other words, just as the form of a ship may be inefficient for high speeds, so it may be for low.

Table XIII. gives the prismatic co-efficients appropriate to all steamers from 100 ft. to 1000 ft. long, and from 10 knots to 28 knots speed, when of the usual ship form and style.

Table XIY. shows the values of the co-efficient G in the Admiralty

speed formula I.H.P.s— 1~ — , when the ship is in agreement with

Rules 26, 27, 28.

If a ship is finer than given by Rule 26, the value of 0 may be increased, as it may be also when the machinery has a higher efficiency than 92 per cent.

Table XY. gives the co-efficient for computing effective {neU) horse- power necessary to overcome skin friction based on Dr. Fr3ude*s

COUBtautB.

44

RESISTANCE AND PROPULSION OP SHIPS.

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BBSIBTANOE AND PROPULSION OF SHIPS.

Immersed Surface Friction.

Table XYI. (page 47) gives a general statement of the results of Fronde's experiments on this subject; they were made on boards '/4c iu. thick and 19 in. deep, which were coated with the substances to be experimented on, and towed edgeways through the water. The resistances are given in lbs. per square foot at the standard speed of 600 feet per minute, and, as the power of the speed to which the friction is proportional is also given, the resistance at other speeds is easily calculated. *

Columns A give the power of the speed to which the resistance is approximately proportional ; columns B give the mean resistance per square foot of the whole surface of a board of the lengths stated in the table ; columns 0 give the resistance of a square foot of surface at the distance sternward from the cut- water stated in the heading.

Table XV.— Co-efficients for Computing: Effective Horse-power required to overcome Skin Friction based on Mr Froude's Constants, as given by Mr A. W. Johns.

If S is the wetted surface in square feet, then

E.H.P. =/. S, where/ has the values given below.

Speed in Knots.

Length of Ship in Feet.

100

160

200

•2468

•2190-

•1942

•1718

•1502

•1308

•1132

•0972

•0827

•0697

•0680

•0478

•0387

•0809

250

800

850

400

460

600

26, . 24, 23, 22,

21, 20, .

19. 18,

17, 16, 16, ,

u,

18, 12.

•2616 •2242 •1988 •1763 •1637 •1340 •1159 •0996 •0846 •0718 •0694 •0489 •0397 •0315

•2477 •2207 •1957 •1726 •1614 •1319 •1141 •0979 •0833 •0702 •0585 •0481 •0390 •0812

•2444 •2178 •1931 •1703 •1494 •1301 •1126 •0966 •0822 •0693 •0577 •0476 •0885 •0308

•2434 •2169 •1923 •1696 •1487 •1296 •1121 •0962 •0819 •0690 •0576 •0473 •0384 •0307

•2415 •2160 •1916 •1690 •1481 •1291 •1171 •0968 •0816 •0687 •0673 •0471 •0382 •0306

•2416 •2162 •1908 •1683 •1476 •1286 •1112 •0956 •0812 •0685 •0570 •0469 •0381 •0304

•2407 •2146 •1902 •1677 •1471 •1281 •1108 •0951 •0810 •0682 •0568 •0468 •0379 •0308

•2399 •2188 •1896 •1672 •1466 •1277 •1106 •0948 •0807 •0680 •0567 •0466 •0878 •0802

In the ahove table skin friction is taken as varying as V^'SaB.'

* NOTB.~See Bule 80.

RBSISTANOB AND PROPULSION OF SHIPS.

47

Table XVI.— Resistances of Surfaces.

Natnre

Length of surface, or diatanoe from cntwatwr, in ftoet

of

2 Feet

8 Feet

80 Feet

fiOFeet

Sorfice.

A

B

C •890

A 1-86

B •825

C

•264

A 1'85

B

•278

C

A

1 B G

i •250 -226

YamiBh, .

2-00 -41

•240

1^88

Paraffin,

1^96 -88

•870

1-94

•814

•260

1-93

•271

•237

• • •

1 ■ • • • • •

Tinfoil, .

2-16 -80

•295

1-99

•278

•263 1 -90

•262

•244

1-88

•246 282

Calice, . .

1-98J -87

•725

1^92

•626

•504 1^89

•581

•447

1^87

•474 -428

Fine sand,

2^00 -81

•690

2^00

•688

•450 2^00

•480

•384

2^06

•405 -887

Medium ,,

2 •00, -90

•780

2-00

•625

•488

2-00

•584

•465

2-00

•488 -456

Coarse „

2-00 MO

•880

2^00

•714

'520

2 00

•588

•490

• •

» • • ' • • •

i

True Mean Speed.

To determine the true mean speed of a yess^l when the runs are taken on the measured mile, half with the tide, and half against : —

Example.

Rimf.

Obsenred Speeds.

l8t Means.

2nd Bieans.

8rd Means.

4th Means.

Mean of Means.

Ist 18 5

15 52500 ^

\ 15^478125 15*43125'' True mean speed.

6)94 2

15-70

Ordinary mean

speed.

15*48125

Ordinaiy mean of

second means.

The ordinary mean of second means is generally taken, — as unaroid- able errors of obsenration render the third and following decimal places of rery doubtful yalua.

48 RBSISTANCB AND PROPULSION OP SHIPS.

Find the means of consecutiye speeds continually found until only one remains.

If a, b, c, d, e, and f are the speeds as given of six runs on the measured mile, the ultimate mean of means may be found by the following rule.

Rule 29. Mean speed =(i±fi±Mk+e) + li(c + d)_

Taking the above example by this rule, the mean speed is 15*478 knots. It is, however, usual now when taking the speed as the ultimate mean of means to have an odd number of runs on the mile for greater accuracy in a tideway ; then if five runs are made :—

Mean Speed =l±i^±^^±M±£ ^ 16

Taking the first five runs in the above example, the mean speed is

then 15*525.

Relation of Speeds and Powers.

Oiven two speeds of a vessel, and the corresponding horse-poweiB, to find what power of the speed the horse-power varies as : —

Let 8 and S— the two speeds. „ p and P— the corresponding powers. ,, SB— power of s and S that p and P rtaj m

a» p or X (Log S - Log «)— Log P - Log p

Rule 30. And «- LogP-LogJP.

3". ^ ^' liOgS-Logf

Depth of Water for Speed Trials.

Dr D. W. Taylor's formula :

D is the draught of water of ship in feet.

L is her length in feet.

S the maximum speed in knots.

Rule 30a. Minimum depth = — ^ fathoms.

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52

RBSISTANOS AND PROPULSION OF SHIPS.

The following Table of the % powers of numbers will be of service in all calculations for which displacement is taken as a basis.

Table XVI 1 1. — Two-thirds powers of numbers.

Number.

|rd

Number.

Ird

Number.

|rd

Number.

ltd 1

power.

power.

power.

power. 1

100

21-54

480

61-80

860

90*43

1240

115-42 1

110

22-96

490

62-15

870

91*18

60

116-04 1

120

24-38

500

62-99

880

91*88

60

116-66

180

25-66

510

68*88

890

92*62

70

117-27

HO

26-96

620

64-66

900

93-22

80

117-89

150

28-28

530

65-49

910

98-91

90

118-50

160

29-47

540

66-31

920

94*69

1300

119*11

170

80-69

550

67*18

930

95*28

io

119-72

180

81-88

660

67*94

940

95*96

20

120*33

190

88-05

570

68*74

960

96*64

80

120*94

200

84-21

580

69*54

960

97-82

40

121*55

210

85-88

590

70-34

970

97-99

60

122*16

220

86-44

600

71*18

980

98-66

60

122*76

280

87-54

610

71*92

990

99*83

70

123*35

240

88*62

620

72-71

1000

100*00

80

123-96

250

89-68

630

78-49

10

100*66

90

124-65

260

40-74

640

74-26

20

101*88

1400

125-14

270

41-78

650

76-03

80

101*99

10

125-74

280

42*80

660

76-80

40

102-65

20

126-33

290

48-81

670

76-67

60

108*30

30

126-92

800

44-81

680

77-88

60

108-96

40

127-51

810

45-80

690

78*08

70

104-61

60

128*10

820

46-78

700

78-84

80

105*26

60

128-69

880

47-75

710

79-59

90

105-91

70

129-28

840

48-71

720

80-83

1100

106-56

80

129*87

850

49-66

730

81-07

10

107-20

90

180-45

860

50-61

740

81*81

20

107*86

1600

131-03

870

51-64

760

82-55

80

108-49

10

181-61

880

52-46

760

83-28

40

109*13

20

182*19

890

53-88

770

84-01

60

109-76

30

182*77

400

54-29

780

84-73

60

110*40

40

183*36

410

65-19

790

86-46

70

111*03

60

133*98

420

56-08

800

86-18

80

111-67

60

134-60

430

56-97

810

86-89

90

112-30

70

185-08

440

67-85

820

87-61

1200

112-92

80

185-65

450

58-72

880

88-82

10

118-55

90

136*28

460

59-59

840

89-03

20

114-17

1600

186-80

470

60-46

860

89*78

80

114-80

10

187-87

TABLE XVIII. — TWO-THIRDS POWERS OF NUMBERS.

63

Table XVIII.

—Two-thirds powers of numhers^amtinued.

Nnmbtt.

}id

Namber.

fid

Nmnber.

Ud

Number.

|rd

power.

power.

power.

power.

1620

187-93

2080

162-94

2920

204-28

8700

241 -80

80

138-60

2100

163*99

40

205-22

80

242-65

40

139*06

20

166-02

60

206*16

3800

248*51

50

139*63

40

166 05

80

207-08

20

244-86

60

140*19

60

167-09

8000

208-01

40

246 22

70

140-75

80

168-12

20

208-93

60

246-07

80

141-32

2200

169*15

40

209-85

80

246-91

90

141-88

20

170-17

60

210-76

3900

247-76

1700

142-44

40

171*19

80

211-68

20

248-61

10

143-00

60

172*20

8100

212*69

40

249*46

20

143-55

80

173*22

20

213*51

60

260*29

30

144-11

2300

174-24

40

214*42

80

251 -14

40

144*66

20

175-24

60

215-33

4000

261 *98

50

146-22

40

176*26

80

216-24

20

252-82

60

145-77

60

177-25

3200

217-15

40

263-65

70

146-32

80

178*26

20

218-06

60

254*49

80

146-87

2400

179*26

40

218-96

80

265*83

90

147-42

20

180-25

60

219*85

4100

256*16

1800

147-97

40

181 *24

80 ■

220*76

20

257-00

10

148-52

60

182*28

8800

221-65

40

257*88

20

149-06

80

188*22

20

222-64

60

258*67

80

149-61

2500

184*20

40

223*44

80

269-49

40

150*15

20

186-18

60

224-34

4200

260*81

50

150-70

40

186-16

80

225-22

20

261*14

60

151*24

60

187-14

3400

226-11

40

261*96

70

151*78

80

188*11

20

226*99

60

262*78

80

152-82

2600

189-08

40

227*88

80

268-60

90

152-86

20

190*05

60

228*76

4800

264-42

1900

153*40

40

191-02

80

229-64

20

266*24

10

153*94

60

191*98

3500

280*62

40

266-06

20

154-47

80

192-98

20

231 -40

60

266-87

80

156*01

2700

198*89

40

282-27

80

267*69

40

166-54

20

194*86

60

238-14

4400

268*51

50

156-08

40

196*80

80

234-02

20

269-82

60

156-61

60

196*75

8600

234-89

40

270-18

70

157-14

80

197-71

20

286-76

60

270-95

80

157-68

2800

198-66

40

236-62

80

271*76

90

158-21

20

199-60

60

237*49

4600

272-66

2000

158-74

40

200*64

80

288*86

20

278*87

20

159*79

60

201 -48

8700

239-22

40

274*17

40

160-84

80

202*42

20

240*08

60

274-08

60

161-89

2900

208*86

40

240-94

80

275*78

54

REST8TANGB AND PROPULSION OP SHIPS.

Table XVIII.— Two-thirds powers of numbers-— eon^muMf.

Nnmber.

ird

Number.

}rd

Number.

frd

Nnmber

|rd

power.

power.

power.

power.

4600

276-68

6150

335*67

8300

409*93

10,900

491 '61

20

277-89

6200

337*49

60

411*57

11,000

494-61

40

278-19

60

889*30

8400

418-22

100

497*60

60

278-99

6300

341*11

60

414-86

200

600-68

80

279-78

50

342*91

8600

416*49

300

603*66

4700

280-68

6400

344-71

60

418*12

4C0

606*68

20

281*88

60

346-50

8600

419*76

600

609*48

40

282-17

6600

348-29

50

421 *37

600

612-48

60

282-96

50

850-07

8700

423 -00

700

616-38

80

283-76

6600

861 -86

50

424*62

800

618-31

4800

284*66

60

353-62

8800

426*24

900

621 23

20

286-83

6700

356-39

50

427*86

12,000

624-16

40

286-11

60

857*16

8900

429-46

100

627*06

60

286-90

6800

868*98

50

481-06

200

629*95

80

287-68

60

860-68

9000

432*67

800

532-88

4900

288-47

6900

862 48

60

434*27

400

585-72

20

289-26

60

864-18

9100

435-86

600

588-60

40

290 06

7000

866-98

60

437-46

600

541-48

60

290*84

60

867*67

9200

489*04

700

544-84

80

291*62

7100

869*41

60

440*64

800

547*20

6000

292*40

60

871*18

9800

442-23

900

560-04

60

294-34

7200

872*86

60

443*82

18,000

662*88

6100

296-27

60

874*68

9400

446-40

100

655*70

60

298-21

7300

876*31

60

446*97

200

668*68

6200

800-16

50

378*02

9600

448*64

300

561*85

60

802-06

7400

379*74

60

450*11

400

564 16

6800

808-98

60

381*44

9600

461*68

600

566*96

60

806-89

7600

383*16

60

463*26

600

569-76

6400

807-80

60

384-85

9700

464*82

700

572-54

50

309-68

7600

886*55

50

456*39

800

575-88

6600

811-68

60

888*24

9800

467-96

900

578-10

60

313-46

7700

389*93

60

469*60

14,000

580-88

6600

816-34

60

391*62

9900

461*06

100

683-63

60

817-21

7800

393-30

50

462*61

200

686-38

6700

819-09

50

394*98

10,000

464*16

300

689*13

60

320-95

7900

396-66

100

467-25

400

691 -88

6800

822-81

50

398-33

200

470*33

600

694*61

60

824-66

8000

400-00

800

473-39

600

597-84

6900

326-61

50

401 -66

400

476-44

700

600*07

60

328-85

8100

403-32

500

479-49

800

602*80

6000

330-19

60

404*97

600

482*54

900

605-51

60

832*02

8200

406-68

700

486*67

16,000

608-22

6100

883-86

60

408*28

800

488-60

15,100

610*92

TABLE XVIII. ^TWO-THIRDS POWERS OP NUMBERS.

55

Table XVIII.— Two-thirds powers of numbers— continued.

Number.

ird power.

Nnmber.

ird power.

Number.

ird power.

Number.

ird power.

16,200

613-61

19,600

724-5

23, 800

827-4

28,100

924-3

300

616-30

600

726-9

,900

829-7

200

926-5

400

618*98

700

729-4

24,000

832-0

300

928-7

600

621-66

800

731-9

100

834-4

400

930-9

600

624-33

900

734-4

200

836-7

500

933-0

700

627-00

20,000

736-8

300

839-0

600

935-2

800

629*66

100

739-2

400

841-8

700

937-4

900

632-32

200

741-7

- 500

843-6

800

939-6

16,000

634-97

300

744-2

600

846-9

900

941-7

100

637-61

400

746-6

700

848-1

29,000

943*9

200

640-24

600

749-0

800

860-4

100

946-1

300

642-87

600

751-5

900

852-7

200

948-3

400

645-50

700

753-9

26,000

855-0

300

950-4

500

648-12

800

756-3

100

867-3

400

952-6

600

650-74

900

758-8

200

859-5

600

954-7

700

653*35

21,000

761 2

800

861-8

600

956-9

800

656-96

100

763-0

400

864-1

700

959-1

900

658-66

200

766-0

600

866 4

800

961-2

17,000

661-16

300

768-4

600

868-6

900

963-4

100

663-74

400

770-8

700

870-9

80,000

966

200

666-83

500

773-2

800

873-1

250

970

800

668-91

600

775-6

900

875-4

600

976

400

671-48

700

778-0

26,000

877-6

760

981

500

674-05

800

780-6

100

879-9

81,000

987

600

676-62

900

782-8

200

882*1

250

992

700

679 18

22,000

785-1

800

884-4

500

997

800

681 -74

100

787-5

400

886-6

760

1002

900

684-29

200

789-9

500

888-9

32,000

1008

18,000

686-83

300

792-3

600

891-1

250

1013

100

689-37

400

794-6

700

893-3

500

1018

200

691-91

500

797-0

800

895-6

750

1023

300

694-44

600

799-4

900

897-8

33,000

1029

400

696-97

700

801-7

27,000

900-0

250

1034

600

699 49

800

804-1

100

902-2

600

1039

600

70201

900

806-4

200

904-4

750

1046

700

704-52

23,000

808-8

300

906-7

34,000

1060

800

707-03

100

811-1

400

908-8

260

1066

900

709-54

200

813-4

500

911-1

600

1060

19,000

712-0

300

815-8

600

913-3

750

1065

100

714-6

400

818-1

700

915-5

36,000

1070

200

717-0

500

820-4

800

917-7

500

1080

300

719-6

600

822-8

900

919-9

36,000

1090

400

722-0

700

8-25-1

28,000

922-1

600

1100

56

TRIPLE VERSUS COMPOUND ENGINES.

Table XVIII.-

-Two-thirds powers of numbers— contiiiiLed.

Number.

frd

Number.

frd

Number.

frd

Number.

{rd power.

puwer.

power.

1179

power.

37,000

1110

40,500

44,000

1246

50,000

1357

500

1120

41,000

1189

500

1256

51,000

1375

38,('00

1130

500

1199

45,000

1266

52,000

1393

500

1140

42,000

1208

46,000

1284

53,000

1411

39,000

1150

500

1218

47,000

1302

54,000

1428

500

1160

43,000

1227

48,000

1321

55-000

1446

40,000

1170

600

1237

49,000

1339

66-000

1463

TRIPLE VERSUS COMPOUND ENGINES.

The great economy resulting from the use of high-pressure steam is due to the fact that the increased pressure is obtained by the expendi- ture of an amount of heat quite insignificant compared with the additional amount of energy it renders available. The following tabular statement will make this clear at a glance : —

Table XIX.— Steam Pressures and Efficiencies.

aa

«

09 •

ht ca

bog,

M n

o

2

^

30

75

125

175

225

0 a

GQ "^

F.

F. 320" 353** 377* 397V

Total effective

external work by

one pound of steam

in ft. -lbs.

Heat used per 1000

ft. -lbs. of work done.

Thermal units.

Theoretical saving

of fuel at each

step per cent.

126,256

8-696

• • *

174,472 6-373

26-7

206,994

5-420

14-9

231,200

4-833

10-8

255,000

4-425

8-4

Note, — The release pressure is taken to be 10 lbs. per square inch, absolute, in each case, and a back pressure of 4 lbs. per square inch, absolute, is assumed.

That is to say, — an engine using steam of 125 lbs. pressure should, other things being equal, consume nearly 15 per cent, less fuel than one using steam of 76 lbs. pressure; and one using steam of 175 lbs. pressure should effect a further saving of nearly 11 per cent., — so that, by using 175 lbs. steam in place of 75 lbs., a saving of over 23 per cent, should be effected.

RATIOS OF OTLIlTDBBa.

67

In practice, however, a two-stage compound engine, using ^team of 140 lbs. pressure, shows very little economy over a simple engine using 90 lbs. steam ; whilst a triple -stage engine using 140 lbs. steam shows even a greater economy than is theoretically due to the increased pressure. This is due chiefly to the diminished range of temperature in each cylinder, and the low pressure on pins, guides, and bearings.

The actual amount of fuel saved by using a triple engine, working at 1 60 lbs. pressure, in place of a compound engine using, say, 76 lbs. steam, is nearly 25 per cent. ; and a quadruple engine with 200 lbs. saves more still, due to the higher pressure and greater number of stages of expansion.

When the average magnitudes of the stresses set up in the two types of engine are compared, the result is again greatly in favour of the triple.

Compare a three- crank triple engine with an ordinary compound, having same size of L.P. cylinder, same length of stroke, and develop- ing the same power, — the one using steam at 150 lbs., and the other at 75 lbs. ; also let the referred mean pressure be 24 lbs. in each case, and the efficiency of the expansion be the same in the two cases. Then, further, let the L.P. piston area be represented in each case by the number 14 ; the H.P. area of triple by 2, and the H.P. area of compDund by 4, and the M.P. area of triple by 5. Then, if the equiva- lent, or referred, mean pressure is equally obtained from the cylindera in each case, the relative work done will be as follows : —

Triple Engine.

/24 14\ H.P. cylinder, 2 x I -^ x -g- )or 112.

/24 14 M.P. ., 5x[^-g-x-^

L.P.

»>

it

UX3^

jorll2. or 112.

Compound Engine.

r^ ^ ,. ^ /24 14\

H. P. cyhnder, 4 x I y x -7- 1 or 1 68.

24 L.P. „ 14X-0- or 168.

That is, — the average stress on the rods, columns, guides, &c., is 60 per cent, more with the compound than with the triple engine. The triple engine is cdso better balanced than the compound, works with less vibration, gives a more equable turning moment, and con- sequently a higher efficiency of propeller.

It is not surprising, therefore, that the triple compares so favourably with the compound as regards wear and tear.

RATIOS OF CYLINDERS.

Two- Stage or Compound Engines.— Engines of this type are still commonly fitted in paddle vessels, and in small screw steamers ; as also for many auxiliary purposes, such as for driving independent air and circulatingpumps, feed pumps, dynamos, &c.

When fitted in Paddle vessels, the boiler pressure is usually from 70 to 100 lbs. for oscillating engines, and from 90 to 120 lbs. for other types, — the latter pressure mostly with diagonal engines.

But considerations of weight and bulk preclude the adoption of high ratios, and experience has shown that a ratio of about 1 : 3*25 for

58

RATIOS OF CYLINDERS.

pressures up to 110 lbs., and for 140 lbs. 1 : 3*8 is quite satisfactory. The extra quantity of coal to be carried is of little consequence where the voyage is only three or four hours' duration.

The ratios of cylinders for auxiliary engines are also determined more from considerations of weight and bulk than of economy, and with little regard to boiler pressures, — with the result that they are rarely made so great as in the case of the propelling engines, even when the auxiliary engine must run hour for hour with the main engines ; in practice this ratio is generally about 1 : 2'5 to 1 : 3 for cylinders side by side, and 1 : 8*5 to 1 : 4 for tandem engines. In Naval practice, when the boiler pressure used was 300 lbs., the cylinders of compound auxiliary engines were only made 4 to 1.

Three-sta^^e or Triple eng^ines, and Four-Stage or Quadruple eng^es. — In the case of main or propelling engines for merchant or mail steamer^, space and weight are, within ominary limits, of very little consequence, whilst coal consumption is of the utmost import- ance ; L. P. cylinders are therefore usually large enough to expand the steam to the full economical limit, — of say, 6 lbs. absolute.

The ratios of cylinders depend largely on the rate of expansion at full speed. The following holds good in practice : —

Rate of expansion = >Mute pressure^

For Naval engines, Q = 21.

In express steamers short voyage, Q = 19. „ „ long „ Q = 18.

Passenger cargo steamers, Q = 17.

Tramp cargo steamers, Q :^ 16.