the design and construction of power workboats

7/28/2019 The Design and Construction of Power Workboats

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TkeDesign ana Construction

ofPower WorKDoats

byArthur F. Johnson, N. A.


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Copyri^Kt in tlie United States and Canadaand

Entered at Stationers* Hall, London1920

By The Penton Publisking CompanyCleveland, Oliio, U. S. A.

All Rights Reserved Tjl/^

^4Library

ti


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Naval architecture as applied to power worJi-boats lacks literature; perhaps because bigger gameis more absorbing. When it is realized that thefuture inland waterways of this country must bedeveloped and utilized; also that power boats willprovide the means of avoiding the repetition oflamentable inefficiency in conveying the productsof our interior to the principal ports or centers ofdistribution, proper design will be no small factorin the solution of the problem.

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Table of ContentsChapter IAdvantages and Classifications 1Chapter IIAnalyzing Operating Conditions 5Chapter IIIBuoyancy, Draft and Displacement 9Chapter IVLaying Down and Fairing the Lines 15Chapter VStem, Keel and Stern Design 19Chapter VIApplication of Steel Construction 25Chapter VIIWood and Steel Transverse Framing 29Chapter VIIIDesign of Longitudinal Framing 33Chapter IXBulkheads Demand Careful Planning 37Chapter XHull PlanksFenders^Bilge Keels 43Chapter XIDecks for Wood and Steel Boats 47Chapter XIIConstructing the Deck House 53Chapter XIIICompanionsHatchesAwnings 59Chapter XIVMatsDavitsWinchesWindlasses 65Chapter XVAnchorsTowingDeck Drainage 71Chapter XVIAuxiliary Machinery and Quarters 75Chapter XVIIFood Storage, Heating and Lighting 79Chapter XVIIIPainting Structure and Sheathing 83Chapter XIXHow Concrete Power Boats Are Built 87Appendix I Tables of Scantlings for Power Workboats 93Appendix IIDesigns and Details of Typical Power Workboats 101

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List of IllustrationsPage j

Fig. 1Cost Chart of Power Vessels Under Normai. Building Conditions (Commercial) 5 |Fig. 2Cost Chart of Large Power Vessels (Commercial) Under Normal Building Conditions 6 |Fig. 3Character Curves Sternwheel Power Boats (Wood) Less Than 100 Feet Long 6 |Fig. 4Hull Proportions Sternwheel Power Vessels Over 100 Feet Long 7 |Fig. 5Hull Proportions Power Tugs Over 60 Feet Long 7 jFig. 6Character Curves Power Lighters 8 |Fig. 7Hull Proportions Small Screw Vessels (Wood) 8 |Fig. 8Shows Water Pressure Acting on a Floating Vessel 10 |Fig. 9Illustrates Relation Between Draft and Displacement 11 |Fig. 10Indicates the Utility of Reserve Buoyancy 11 |Fig. 1 1How External Force Causes Heei.ed-Over Position 12 jFig. 12Path of Water Around a Box-Shaped Hull 12 |Fig. 13Gradual Stream-Line of a Properly Formed Vessel 12 |Fig. 14Lines of a SO-Foot Power Tug 14 |Fig. isVarious Forms of Stems IS |Fig. 16Various Types of Sterns 16 |Fig. 17Sterns for Shallow Draft Vessels 17 |Fig. 18Paddle Wheel Stern 17 |Fig. 19Illustrating a Typical Body Section 18 |Fig. 20Stem of a Wooden Tug 19 |Fig. 21Stem of a Small Power Workboat 19 |Fig. 22Stem of a Large Vessel 2S0 Feet Long 19 |Fig. 23Stem of a Large Wooden Vessel 20 |Fig. 24Construction of Spoon Bow for Shallow Draft Boats 20 jFig. 25Clipper Stem of Auxiliary Sailing Vessel 20 |Fig. 26Construction ok Bottom Girder of Large Wooden Ship 20 jFig. 26aHow Keel Bolts are Countersunk 21 jFig. 27Keel of a Wooden Schooner 21 |Fig. 28Keel of a Wooden Tug 21 |Fig. 29Keel of a SO-Foot Workboat 21 |Fig. 30Keel of Shallow Draft Vessel 21 1Fig. 31Overhung Transom Stern of Auxiliary Schooner 22 iFig. 32Stern of Tug or Lighter With Single Deck and Guard Timber 22 |Fig. 33Transom Stern for Small Boat With Metal Rudder 22 |Fig. 34Compromise Sterns Seldom Used on Workboats 22 IFig. 35Shallow Draft Stern With Stern Wheel 23 |Fig. 36Longitudinal Section of Wooden Tunnel Stern Boat 23 |Fig. 37Cross Sections Showing Different Tunnel Construction 23 IFig. 38Bar Stems and Method of Scarphing 25 |Fig. 39Three Types of Keels of Steel Vessels 25 |Fig. 40Methods of Fitting Keelsons 25 IF"ig. 41Center Keelson with Innercostal Plate 26 IFig. 42^Transverse Section of Double Bottom 26 IFig. 43Construction of Overhung Transom Stern 26 |Fig. 44Attaching Guards and Rails 26 |Fig. 45Construction of Rudders and Strut Bearings 27 |Fig. 46Elevation and Plan of Sternwheel Vessel 27 iFig. 47How the Bottom Plating is Dished for Tunnel Stern 27 1Fig. 48Stern (Or Bow) of Double Ended Steel Ferry Boat 27 IFig. 49Construction for Tugs and Power Lighters 29 |Fig. 50Transverse Framing of Large Wooden Vessels 30 |Fig. 51Frames for Shallow Draft Vessels 30 |Fig. 52Midship Section of Steel Tug or Lighter 30 |Fig. 53Where the Main Deck Overhangs the Hull 31 |P"iG. 54Shallow Draft Vessels Have Straight Frames 31 |Fig. 55Steel Stanchions and Stanchion Heads 32 |Fig. 56Longitudinal Stringers and Shelves For Wooden Tugs; Frames for Shallow Steel Vessels 33 |Fig. 57Cross Sections Showing Fra.vie Construction 34 |

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List of IllustrationsPage

Fig. 58Steel Side Keelsons with Transverse Framing 35Fig. 59Hatch and Cockpit Coaming Construction 35Fig. 60Cross Section of a Tug with Longitudinal Framing 36Fig. 61What Happens When the Bow or Stern Compartment is Flooded 38 |Fig. 62Transverse Watertight Bulkhead of Wooden Vessel Longer Than 125 Feet 38 |Fig. 63Transverse Watertight Bulkhead for Small Wooden Vessel 39 |Fig. 64Cross Sections of Various Minor Bulkheads for Cabins, Etc 39 |Fig. 65.Steel Bulkheads and Fastenings for Wooden Vessels 40 |Fig. 66Shows Method of Fitting "Shoes" at Bulkheads Where Keelsons and Stringers are Cut 40 |Fig. 67Construction of Tank Bulkheads for Oil and Water; Also Metal Bulkheads for Minor Com- I

partments 41 IFig. 68How Stealer Plates are Ln'troduced 43 |Fig. 68-aMethods of Fitting Hull Plating to Frames ; 44 |Fig. 69Construction of Fenders and Bilge Keels 45 |Fig. 70How Decks are Classified 45 jFig. 71Drawings Showing Contour of Decks and Sheer 4g |Fig. 72Methods of Laying Deck Planks 48 |Fig. 17iCross-Section of Wooden Deck Construction 49 |Fig. 74Construction of Decks of Steel Vessels 50 |Fig. 75Construction of Ceilings and Double Bottoms 50 |Fig. 76Contour and Construction of Wooden Deck Houses 54 1Fig. nConstruction Details of Steel Houses 55 |Fig. 78Watertight Doors, Air Ports and Dead Ligh fs 56 |Fig. 79Construction of Hinged Windows and Skylights 57 |Fig. 80Wood and Steel Companions 59 |Fig. 81Detail Construction of Companion Slides and Hatches 60 IFig. 82Watertight Hatches and Manholes 61 IFig. 83Construction Details of Ladders and Rails 62 IFig. 84Awning Stanchions and Fittings 63 iFig. 85How Pole Mast and Boom is Fitted 65 |Fig. 86Construction and Install.\tion of Steel Masts, Also Boom Crotch 66 IFig. 87Davits and How They are Installed 67 IFig. 88Winches, Windlasses and Ground Tackle 68 IFig. 89Anchors, Chocks and Hawse Pipes 72 |Fig. 90Towing Bitts and Knees "j-x, |Fig. 91Chocks and Cleats "ji |Fig. 92^Fuel or Water Tanks, Flat Side Type 75 |Fig. 93Installation and Equipment of Fuel Tanks 76 |

Detail of Inlet Connection for Pipe Suctions from Sea 76 1Detail of Soil Pipe Discharge Connection 77 1Detail of Scupper from Tiled Toilet Space 77 |

I Fig. 95Built-in Refrigerator in Cabin Trunk of 50 to 75-Foot Power Boat 7g |I Fig. 96Construction of Refrigerator Door 79 |I Fig. 97Interior of Stack with Tanks 80 jI Fig. 98Ventilating Equipme.mt 80 |I Fig. 99Ventilating Equipment 80 II Fig. 100Pipe and Transom Berths 81 II Fig. 101Bilge Keels and Sheathing 84 II Fig. 102How Wood Sheathing is Fitted on Wooden Hulls 85 II Fig. 103Typical Section of a Concrete Hull Under Construction 88 II Fig. 104Metal Clips Used to Support Longitudinal Rods 89 |I Fig. 105Method Used in Holding Rods in Place for Pourinc; Forms 89 II Fig. 106Molded Guide Bar Punched to Receive Rods. This is a Very Satisfactory Method Used with |I Excellent Results 89 II Fig. 107Construction of Stanchions and Girders 90 |I Figs. 108 and 109Bow and Stern Construction for a Concrete Workbjat 90 |I Fig. 110Details for Attaching Miscellaneous Fittings 91 |^UMuiiniiittiiMuniiiiiuuiiuiiuiimiMiiwimiiiiiiiiiiiiiiHiiniiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiin^


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Arthur F. Ji.hnson, N. A., aulhcr cf De-sign and Construction oj Power Wcrkhoats,appears here in the uniform oj Assistant MarineSuperintendent of the U. S. Army TransportService. Besides being educated as a navalarchitect and marine engineer, h: has had wideexperience in th: U . S. Engineer's Departmentand in shipbuilding yards and as DesigningEngineer for the Fabricated Ship Corporation,Milwaukee, Wis., so that ht has a practical aswell as a theoretical knowledge of the subject.Mr. Johnson, at th: present writing is Produc-tion Manager of Nelson Purchasing Organiza-tion, Chicago, III.

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CHAPTER IAdvantages ana Classincations

HE utilization of vessels, propelled by internal points should be understood by owners, operators andcombustion engines, for commercial transporta- builders.^ J tion by water is no longer in the experimental^^^^ stage; nor has there been a dearth of literaturesetting forth the general characteristics of the numeroususes to which this type of craft has been adapted. From thevery first, good engineering portended success of this class ofvessels, since there can be no sounder logic than that

In general power workboats may be classified underthree main headings: First, service in which engaged;second, material of which constructed; and third, typeand arrangement of propelling machinery.With respect to service, the first consideration iswhether the waters navigated are to be "open" or

chemical energy as contained in fuel will produce maxi- "sheltered;" that is, whether the vessel is to go to seamum power when converted into mechanical energy atthe nearest practicable location to the point of applica-tion of the power.Whereas, in steam-propelled craft, the latent energy

in fuel was first converted into heat of gases due tocombustion, these gasesthen transmitting theirheat to water in aboiler, generating steam ;this in turn passing tothe engine, losing con-siderable heat contenten route; in a combus-tion engine all the en-ergy conversion takesplace in the cylinders.This not only resultsin saving of weight byomission of boilers andincreased space for car-go storage due to lesserspace occupied perhorsepower, but also theabolition of heat lossesand the carriage of wa-ter for boiler feed.These advantages

were at first offset bypractical defects in com-bustion engine design,lack of skill on the partof the operators and thecustomary conservativeframe of mind on thepart of vessel ownerswhich is inevitable toall radical innovations

KUMTUX, LUMBER TOW BOATShe is 65 feet x 16 feet and is powered with a 110-horsepower Standard-Corlissengine. She is owned hy the Puget Sound Tow Boat Co. and has given herowners great service

or to operate in rivers and harbors.Seagoing vessels to date have been mainly cargo car-

riers (wooden or steel) or auxiliary sailing craft. Theconstruction in these being identical with that of steamers,has been thoroughly treated in other works of ship

design.V e s s e Is traversingcoastwise, harbor orinland waters arethose here to be dis-cussed and embraced'(1) Ferries:

(a) Fast passenger.(b) Passenger and

freight.(c) Car.

(2) Tugs.(3) Power lighters.(4) Tank boats:

(a) Water.(b) Petroleum prod-

ucts.(5) Trawlers.(6) Shop boats:

(a) Repair boats:(Machine shops)(Welding plants)

(7) Pumping andwrecking boats.

Passenger ferries varyfrom fine-lined relative-ly fast vessels of from50 or 60 feet, to 200feet in length. Depend-ing upon the length ofrun they may vary inspeed from 10 to 20

in industry. The tendency to let others pay for the experi-ments incidental to practical perfection delayed progress indevelopment.

miles (statute). Their characteristic arrangement is to affordmaximum passenger accommodation : Sleeping, mess accom-modations and sanitation for the large craft on long runs(seldom more than for one night) ; and maximum seating,sanitary and sometimes messing provisions for relatively shortower Boats Have Replaced Small Steamers

Since power boats, particularly those using the lighter runs not exceeding one day (sunrise to sunset)fuels, have practically replaced the small steamers of fore-gone days, and the ones requiring considerable powerand cheap fuel have long since shown the desirability ofdiesel engines ; effort should be made to co-ordinate thevaluable experience of operators and record the featuresof design in power boats. This is particularly desirablewith respect to the smaller vessels, where ordinary power-

Jitney Boat for CommutersA recent innovation in this connection has been the

"jitney boat", making runs from points within an hour'srun of a city or railroad depot, and used for transportingcommuters.Passenger and freight ferries of moderate speed (8 to

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The Design and Construction of Power Work Boatsfrom 50 to 200 feet are becoming in- welding. With the prevailing pricescreasingly popular as sources of profit, at present, and as long as steel ex-The holds and main deck are employed cecds $0.03 per pound, this would notfor freight storage and the superstruc- be desirable, however,ture houses the passengers. A cargo Composite vessels arc those withboom forward facilitates lifting heavy wooden hull planking and steel framing,weights, the hoisting winch being geared For boats under 100 feet long, thisfrom the main engine or being an inde- is scarcely a desirable construction,pendent machine. There is a single- though in larger ones it is being e.x-ended type for voyages of more than tensively employed.one-half hour or so ; the ones for short Wooden construction is the mostand frequent trips as well as the car universally employed and desirable forferries being double-ended. They may vessels less than 100 feet long. Thisbe propelled by screws or paddle wheels, is due to the facility in working theTugs comprise probably the most nu- material, simplicity of equipment neededmerous class of the commercial power in building yards and also to the factboats. Their lengths are from 35 to that vessels up to this size are amply150 feet and speeds (when not towing) strong when built of wood. Steel, if toofrom 8 to 12 miles. Many of the con- light, has not the requisite stiffness andventionalities in tug design could be corrodes through quickly. If the steelimproved or dispensed with to the ulti- is made heavier, care must be takenmate betterment of the whole. This that the vessel is not of greater dis-will be elaborated upon subsequently, placement than would be the case in aThe essential to a tug's successis great pulling power at slowspeeds, requiring a heavy-duty,slow-turning engine coupled to apropeller of large diameter andlow pitch ratio (0.9 to 1). Powerlighters are modified types withlarge decks and hold space forcargo and a boom for loading.Tank boats, as their name im-plies, carry water or petroleumin bulk, the form being full andthe engines aft (at the stern).Trawlers are of tug design, fit-ted with hoisting booms andfish tanks. They attained no-toriety in the recent war bytheir utility in mine sweeping.Shop boats, carrying machineshop tools, welding plants andapparatus are becoming numer-ous. They are constructed witha view to bringing the repairequipment to the disabled plant, in- wooden one of corresponding size andstead of requiring the cripple to visit strength.the shipyard. Workboats used for salv- Power workboats of wood are muching and wrecking purposes carry a mis- more substantially built than are pleas-cellaneous equipment, such as pumping ure craft and it is to establish stand-apparatus and machines for handling ards and details in these practical ves-divers. With the value of vessel prop- sels that this work is undertaken.

HALIBUT SCHOONER COXSTANCEOne of the finest boats ever built for halibut service-measures 87 feet on deck, 18 feet beam and carrieshorsepower Standard-Frisco engine

erty going up sky high these boats arebecotning profitable.

Steel Too High for Small BoatsBy material of construction is meant

that of which the prmcipal strengthmembers and hull are composed. Steelis most universally employed in vesselsover 100 feet long, though it has beenused in pressed form for small powerand life boats. In the writer's opinionpowerboats as small as SO feet long, pro-

Reinforced concrete promises to be-come extensively used in boat construc-tion, particularly where a considerablenumber of the same form and sizeof vessels are produced. It is no longeran experimental construction, barges andseagoing vessels now building being theresult of observing, for years, thosealready in service.

Concrete Boats for Inland WatcrivaysSteel and concrete having nearly the

viding they are full lined, could -be built same coefficients of expansion and theof light galvanized steel shapes and fact that painting, copper sheathing andplates, riveting being replaced by spot fouling of bottoms will be troubles of

the past as well as that deteriorationis negligible, point to extensive utilizationof this desirable material, particularlyfor inland waterways. A very richmixture (l-l-}^-3) of concrete, withgravel passing Y^-'mch mesh, is usedfor the hull. This is molded or "shot"onto galvanized wire mesh supportedby ordinary reinforcing rods, the to-tal hull thickness varying from 2 to5 inches. Internal hull structure em-bodies reinforcing steel skeletonwork with a leaner concrete (1-2-4) or(1-3-5) again using fine gravel. Thedensity of concrete determines itslife, strength and watertightness aswell as its elasticity. Ordinary con-crete, as commonly used ashore,would not prove satisfactory for ves-sels. If the ships are molded, stand-ard metal molds may serve for nu-merous hulls, but if one or two onlyare to be built, the "gunning" meth-od is more desirable, particularly

in view of the fact that a morenearly ship-shape form can bebuilt in this manner. Moldedhulls have resulted in crude-ness of lines and while this isimmaterial at low speeds, tugsor finer craft would requireexcessive power unless morerefined in form. The type andarrangement of the propellingmachinery together with themeans of converting the powergenerated into propulsive thrustwill not be elaborated uponexcept wherein they affect hullconstruction or arrangement.The power plant itself may becombustion engines of any oneof the following types :(a) Diesel or oil engines, op-

erating on two-stroke orfour-stroke cycle usingheavy oil fuel (between14 degrees and 23 de-grees Baume), wherein fuelis i n j e c ted as spray intothe cylinders with compressedair and ignition results fromhigh compression of the charge.Revolution ISO to 300.

"Semidiesel"or heavy distillateengines, using kerosene or dis-tillate fuel with hot bulb igni-tion or spark. These enginesare similar to ordinary gasolinemachines, but operate at slowspeed and are much more heav-ily constructed. Revolutions from200 to 600.

Gasoline engines (usually four-stroke cycle) using light pe-troleum distillate, with electricalignition, low compression andoperating (in heavy marine work)

-She140

(b)

(c)


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Advantages and Classificationsbetween 350 and 800 revolutionsper minute,

(d) Gas producer plants using coal,wood or other gaseous fuel.Diesel or oil engines being relatively

high powered, are not much used insmall commercial power boats. An in-teresting departure from this generalityis the government tug Manteo whichhas a 100-horscpower, 2-cycle, dicsel en-gine and which is only 50 feet long.

"Semidiesel" engines, a rather vagueand incorrect term, arc excellent forheavy duty service providing the oper-ator understands them. Such enginesshould be more extensively utilized thanthey now are, noi only because of thesaving in fuel, but their rugged con-struction and ability to run continuouslyif properly attended. There have beensome sad experiences, however, wheninexpertly handled.

Gasoline, or light distillate engines,of heavy duty design, are usually directconnected to the propeller and are themost generally employed. Sometimes,in order to conserve space and weight,small, high-speed engines (900 to 1200revolutions per minute) are installedwith a reduction gear to the propellershaft. This system is comparatively re-cent in ships, though long used in auto-mobiles. It promises to become pop-

ular if light fuels do not attain pro-hibitive prices.Gas producer plants have never been

extensively employed, though when prop-erly designed and operated they haveproved practical and economical. Theyconsist of a producer proper, where fuelis caused to give off its combustiblegases through distillation, partial com-bustion and sometimes chemical combina-tion with water vapor.The fuels used may be wood, coal

of a low grade or residue combustiblematerial. The gases generally pass througha "scrubber" where foreign matter isremoved by spray or other means andthence to an internal combustion engine.The arguments against producer plants

arc : Excess weight and space occupiedby the plant, and skill necessary toproper operation.The propulsive mechanism of com-mercial power boats may be propellersor paddle wheels.

Propellers are most commonly em-ployed where light draft is not a factorin design. This is because of their pro-tected location with respect to the hull,which minimizes damage by strikingagainst docks, towed vessels or by roughseas. Another reason is that higherrevolutions with efficient propulsion ren-der them adaptable to direct coupling

with engine shafts, with attendant re-duction in space occupied by machineryof a given power.Paddle wheels (at side or stern of

vessels) are desirable in shoal waterbecause of efficient propulsion underlimited depth of immersion and also fa-cility of repairing buckets damagedthrough striking submerged ol)stacles.The practical range of revolutions inpaddle wheels is between 20 and 40,rendering necessary a reduction in speedfrom engine to wheel. This is accom-plished through belts, gears, chains, ora combination of these.

Propellers in Tunnel BoatsPropellers in tunnels, so that the wa-

ter surface at rest is not more thanone-third of the wheel diameter belowthe upper tip of blades, are frequentlyemployed for shallow draft propulsion.Though the wheel diameter is restrictedand revolutions comparatively high, ex-cellent results have been obtained inthis way, even in tow boats. In these,the out-of-the-way propellers presentan advantage over the projecting paddlewheels, and the lightened and less roomymachinery afford lighter draft on agiven size of vessel or permit of de-crease in vessel dimensions for givendraft and power.


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The Design cud Construction of Pozvcr Work Boats


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CHAPTER IIAnalyzing Operating Conditions

^^^^^HE first essential in selectingm C\ a design of power boat is a^^ J careful study of the require-^^^^ inents imposed by the servicein which it will be engaged.

This will determine the general arrange-ment, degree of equipment, power,amount of fuel, stores and water, ma-terial and construction, etc.

It is assumed that one undertakingthe construction of a commercial vesselwill familiarize himself with these re-quirements by careful study of the localconditions at the terminals and throughthe trade route which the vessel is toply. Conditions are so varied and thecombinations of these so numerous thatexhaustive discussion would scarcely bewarranted.In general the factors encountered are :(1) Character of service.(2) Character of materials ported.(3) Conditions of water traversed.(4) Terminal adaptation to the trade

contemplated.The design as affected by characterof service has already been considered,as have the general features called forin passenger traffic.

Freight may be roughly subdividedinto :(a) Fast package.(b) Perishable.(c) Miscellaneous

slow.(d) Bulk.The first of these

has heretofore beenmost extensive onocean or large in-1 a n d or sea traderoutes, services inwhich natural con-ditions have pro-hibited land trans-portation. There isreason to supposethat with reliableand well adminis-trated inland water-way runs, much ofthis revenue earn-ing cargo could bediverted from thenone too punctualrail routes of thiscountry. This docsnot infer competi-tion, but rather co-operation with therailroads, since

many water routes are shorter betweenterminal points and the question ofcollection and delivery may aflfect to-tal time in transit and portage charges.Fast water freight would work well inconjunction with passenger traffic. It isnot very many years gone that travelerspreferred canals to stage coach and theanalogy still applies insofar as comfortand restful conditions in water travelsurpass those in a sleeping car. It ismerely a question of providing everyconvenience and shortening time intransit which are not insurmountabledifficulties in many overnight runs.

Kinds of freight HandledPerishable freight is of two general

kinds : That which will deteriorate dueto delay in shipment (mainly edibles) ;and that which must be protected fromthe weather. The first of these willrequire refrigeration or ventilation, andthe second merely storage in holds orunder cover. Both of these classes arereadily adaptable to economical waterconveyence, delay at terminals being themost adverse condition to be remedied.

Aliscellaneous slow freight alreadyconstitutes a considerable percentage ofthe total transport material in some

sections of this country and a greaterproportion in many foreign lands thanis generally supposed. It consists ofmany items in variegated sizes fromlarge pieces of machinery to small boxes,cases, castings, etc.Bulk freight lends itself most agree-

ably to storage and terminal loadingand discharge. It consists of coal,brick, petroleum, ore, grain, etc., andrenders possible the design of vesselsspecially fitted to carry the particularcommodity. Maritime traffic in thisclass is also profitable and constantlyincreasing in volume. Freight affectshull design in conjunction with theroute of travel, necessitating large closedholds or being most expeditiously stowedon deck in the open or under cover.The amount to be carried per voyage isdependent upon length of the trip (indistance as well as duration). If the dis-tance is considerable, the decreased num-ber of trips will necessitate a largership that profit may result. On a shortrun the assumption that gross expenseof conveyance is inversely proportionalto tonnage conveyed, does not necessarilyhold, since the increased time for load-ing and discharging may be excessivewhen considering the loss in vessel's

earning power whileidle and the great-er original invest-ment. Again, thedepth, width andcontour of channel,dimensions of locks,wharves and man-euvering space atterminals may beconsiderations af-fecting size, pro-portions and evenpropelling mechan-ism of the vessel.Thus a compara-tively narrow andshallow river withsharp bends, locks,and sometimes rap-ids, would necessi-tate radically differ-ent design fromthat permissiblewith a wide, deepand open stream.Paddle wheel ortunnel-sterned boatswith shallow beamyhulls have arisen


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Tlie Design and Construction of Poiver Work Boats

from the first mentioned natural limila-tions, whereas the normally formedscrew vessel is desirable where these ob-stacles are absent or negligible.

How to Determine First CostWhen the appropriate type and its

lengths have been decided upon, it be-comes necessary to determine the prob-able first cost and also the otherdimensions properly applicable. The idealcondition with respect to funds wouldbe that in which these were ample forthe most desirable type of vessel. Veryoften this is not the case, and modifica-tions in design must be resorted to.

If the total costs of numerous vesselsin a class are plotted as ordinates uponabscissa representing vessels' lengths,it will be found that all the resultingspots lie within an area enclosed by twocurves, which are the maximum andminimum amounts requisite for buildingthis type of vessel for any length.

Figs. 1 and 2 are "cost charts" ofthis nature, the smaller vessels havingcost ordinates to large scale in Fig. 1,while the larger vessels' prices aremodified to suit the limits of Fig. 2.

It will be observed that the screwvessels in Fig. 1 are more costly thanthe shallow draft paddle vessels. Thisis because of the more complex formand rugged structure of the former,requiring more elaborate and carefu!workmanship to withstand the strain?of rougher waters which are navigatedby this class. The same reasoning ap-plies to Fig. 2, where it will be furthernoted that steel vessels are most ex-pensive in either class.

The excess first cost of this materialis more than offset by the gain instrength, durability and carrying ca-pacity, for contrary to general supposi-tion, the total weight of a wood vesselis greater than that of a steel one hav-ing equal strength, while the interiorvolume of the wooden one, representingcargo capacity on given dimensions, isalso less than that in the steel hull.The costs here plotted represent re-

sults of competitive bids during normal

times, contracts having been awardednot necessarily to the lowest, but ratherto the most responsible bidder, as deter-mined by capital and equipment of theboat yard.

If a certain fund is available for theconstruction of power boats, the vari-ous sizes of a given type could bederived as follows : Assume that theamount at hand is $40,000. Then inFig. 1, an 82-foot wooden screw tugcould be built to maximum equipmentstandards and two 87-footers of simplestcharacter in normal times. At presentthe costs would be higherthe abovesum affording a vessel about 70 feetlong, with all refinements and two 40-footers which would be little beyondhull, engine and steering gear.On the other hand, if a vessel of

given length is. to be built, its costrange could be similarly arrived at.In Fig. 1, a 60-foot tug (wooden)would range between $7500 and $23,750.The maximum figures are most nearlyin accord with present mean rates forordinary boats.

Beam Varies on Given LengthFor a given length of vessel, thebeam (width) and the depth may vary

considerably. This variation is limitedin the case of beam, by its effect uponstability and speed for a given power.Also to complicate matters, where theincreased beam heightens the tendencyto resist capsizing force, it will resultin greater resistance to propulsion.The degree to which stability may be

sacrificed to minimizing resistance hasbeen determined within minimum and


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Analysing Operating Conditions

maximum limits, beyond which it israrely and with questionable gain, thatproportions are assigned in design.These proportions are graphically de-

picted in Figs. 3 to 7, and dimensionsfor any length selected from these can-not fail to produce vessels of amplestrength, stability and reasonably speedyin proportion to the power installed.The depth of hull at mid-length is

an index to strength, just as the depthof a girder determines ability to resistdeflection. A deeper vessel on givenlength is relatively stronger than ashallow one.Power of the engine to drive the hull

whose dimensions have been selected,is the next consideration. Too manyvessels, particularly in the "small boat"class, have either too much or too littleenergy in the machines driving them,for a vessel may be over as well asunder-powered. It is fallacious to pre-sume corresponding increase in speedfor additional horsepower.

Further, it is impossible to calculatethe exact resistance of a given sizedboat by direct mathematical analysis.This is because, even with two vesselshaving like dimensions and diplacement,the hull forms may vary considerably.There is at present no precise mathe-matical formula for that peculiarlywarped surface of a hull, and until thisis established (which will only be afteryears of investigation) the only waysto properly predetermine engines, are :

(a) By comparison of results in othersimilar vessels.

(b) By actually towing a model ofthe vessel, to scale, and deriving the

rmmiT

result through the "method of com-parison".The first of these methods is thatmost feasible in power workboat de-sign ; the second, though in large ves-sels usually more reliable, is too elabor-ate and occasionally does not produceresults anticipated, particularly in un-usual forms. Since it is impossible toinstall machinery to scale in the model,or to fit miniature propellers, thereto,considerable experience is necessary to

foretell the energy dissipated betweenengine and the point of expenditure ofpropulsive thrust. Adding to this thecost of a series of models, also the ex-pense of conducting the tests at aproperly equipped model testing basin,the method does not at present justifyits adoption for small commercial boats.

In these, allaround working qualitiesare often superlative to minimum resist-ance at given speed, so that unlesspredecessors of like proportions haveproven uneconomical, the result of ob-serving their features (favorable or not)will ordinarily produce excellent re-sults.To this end. Figs. 3 to 7 have been

elaborated, embracing powers, displace-ments, drafts and speeds of varioustypes. These are characteristics ofmany boats in each class and may beconsidered representative.

Working Out the DetailsAssume that the vessel is to be an

80-foot stern wheel towboat of wood.In Fig. 3, we would derive the follow-ing limits for particulars of the hullby reading up to the various curves asordinate on the abscissa labeled 80:Length, 80 feet.Beam, between 16 feet and 20 feet6 inches.

Depth of hull, SZyi inches and 51inches.

Draft in running condition, 17 inchesand 2SJ4 inches.Displacement (fresh water), between

31 tons and 73 tons.


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The Design and Construction of Poivcr Work Boats1

1i 1

1 11

1 1 1 i !I ' 1

1M I n 1 1 : : 1 1 M li

Brake-horsepower of engine, 37 to 62. derived from the remaining charts ifSpeed (per hour) 6 to 10 miles. other types of vessels are under consid-These preliminary figures may be eration. It should be understood that

the lowest horsepower is the one whichwill drive the narrowest hull at theminimum speed, the higher power inthe narrower boat will probably producethe maximum speed figure, while inthe beamier boat this power will resultin a speed intermediate between maxi-mum and minimum.The next consideration is that of fuelcapacity, the kind having been predeter-mined by considerations of economy,facility of replenishing, etc., in thelocality of the vessels' route. Gasolineand light distillate engines will requireabout a pint of fuel per horsepowerper hour. This figure is high for afuel consumption test with the engineon the blocks at the factory, but it mustbe understood the ordinary workingconditions in the boat will prove lesseconomical, due to wear, leakage, occa-sional overheating and perhaps neg-lect. It is therefore imperative to antici-pate these difficulties by providing fuelample under worst conditions.Fuel oil for diesel engines will be

safely estimated at 0.7 lb. per horse-power per hour.

In our chosen vessel, at 62 horse-power, burning gasoline or distillate,that many pints or 7^ gallons wouldcarry the wider boat eight miles andthe narrower one ten. From this thetank capacity could be determined, de-pending upon facility of re-fueling. Ifthe home dock were capable of re-fillingtanks (a desirable feature) less fuelneed be carried with increase in amountof freight. It should not be necessaryto re-fuel oftener than once per work-ing day, and, of course, if the voyagerequired more time than this, once pertrip, if feasible.The general arrangement will be gov-

erned by type. Accommodations forcrew need only be fitted if these can-not return to their home port nightly,in which case necessary plumbing, lock-ers, etc., must also be installed. A studyof arrangement will later be made, itbeing sufficient for any type to assumea somewhat similar layout to otherboats in the same class, many of whichhave been ably described by currentmagazine contributions.The preliminary study of and deci-

sions with respect to design have nowbeen gone over, bringing us to the stageat which details must be understoodand perfected.


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CHAPTER IIIBuoyancy, Draft ana Displacement

^^^^^^HE first requirement whichM C^\ commercial vessels must have^ } is the ability to float. By^^^ this we mean that they shouldbe suspended on the water's surfaceand that a certain portion of the hullshould be above that surface. Nowif the total weight of a boat be divid-ed by its total watertight volume incubic feet, the resulting figure is thepounds per cubic foot or the "density"of the vessel. If this weight per unitof volume is greater than that of acubic foot of water, the vessel willsink.Fresh water has a weight of 62.5

pounds per cubic foot, while salt wa-ter weighs 64 pounds for an equalvolume. A cubic foot of solid ironweighs 490 pounds and would sinkin fresh or salt water. A cubic foot

of wood which weighs from 30 to 60pounds will float in water. If acubical box, 1 foot on each side, weremade of steel sheets 54 inch thickthe six plates forming the sides wouldweigh 10 pounds each, making a totalweight for the box of 60 pounds. This60 pounds is the density of the boxand since it is less than the weightof a cubic foot of either salt orfresh water, the steel box will float.

In fresh water we could put a loadof 2 pounds in the 60-pound steel boxand it would still float. In salt waterthis load could be 3^2 pounds.We thus see that the difference be-tween the total weight of a floatingbody and the weight of an equalvolume of water represents the cargocarrying capacity and that the same

vessel will carry more cargo in saltthan in fresh water.

Experiment on FlotationTake a shallow tray and weigh it

carefully. Then place a deep bowlin the tray and fill the bowl brimfull of water, taking care that it isjust on the point of overflowing intothe tray but that none of the watergets into the tray. Now weigh asquare block of wood which is abouthalf as wide as the bowl. Place theblock carefully on the water in thebowl. The block will float in thebowl and some of the water will over-flow into the tray. Take the blockcarefully out of the bowl and lift thebowl from the tray, being sure thatno more water spills. Then weighthe tray again with the water which

SCANDIA, SEA-GOING POWER HALIBUT BOAT OF THE TACIFIC COAST


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10 The Design and Construction of Power Work Boatswas displaced from the bowl by thefloating block.Deducting the original weight of

the dry tray from the final weightof the tray with displaced waterwill give the actual weight of thewater. It will develop that the waterdisplaced will weigh exactly whatthe block did.We therefore see that the weightof a floating body is exactly equal tothe weight of water it sets aside ordisplaces.Now imagine that while the blockfloated in the bowl, we had frozenthe water in the bowl. Then if theblock were removed a cavity wouldremain in the ice and this cavitywould have exactly the shape andvolume of that part of the blockbelow the water level. The shapeof this cavity is called the "under-water surface" of the floating body.

If the water which overflowed intothe tray were poured back into thecavity in the ice it would be filledand no water would remain in thetray.This proves that: "The volume of

water displaced by a ship is exactly

First the form of hull is carefullydrawn and its volume is calculated todiflferent heights above the bottom ofthe keel. When the volume to eachlevel or "water plane" has beenformed, determine the weight of anequal volume of the water in whichthe vessel is to float by multiply-ing the number of cubic feet in thehull to each water level by the weightof a cubic foot of water.

In general the ton is used for dis^placement weights in preference tothe pound, that the figures employedmay not be too large. To convertcubic feet of hull volume to thenumber of long tons (2240 pounds)of water displaced by that volume,divide by 35 for salt or 36 for freshwater. This is based on the fact thatone ton of fresh water equals 35 andof salt water equals 36 cubic feet.Suppose that a chart is made where-

on heights above a given base linerepresent draft to scale. On the baseline we can represent displacementin tons or in cubic feet by a hori-zontal scale measuring from left toright. Then if our calculations at2 feet draft had shown the vessel's

8 X 10 X 75 = 41.67 cubic feet144


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Buoyancy, Draft and Displacement 11

Fig. 9 illustrates the relation be-tween draft and displacement withand without cargo. When the vesselis light, "d" is the draft, "D C" thewater line and the rectangle "D C E F"a cross section of the hull below wa-ter. "C B" is the center of gravity ofthe displaced volume and is called the"center of buoyancy". The upwardforce of the water is assumed to beconcentrated at this point.When cargo is placed aboard, thevessel's weight increases and theforce of buoyancy acting in the lightcondition is not sufficient to supportit. The vessel, therefore, sinks tothe new water level "A B" wherebuoyancy as represented by the in-creased weight of displaced waterbecomes equal to the augmentedweight of the vessel, "d' " is the newdraft and "C B' " the new center ofbuoyancy.The height "f" of the deck above

the water line is called the "free-board". It is a measure of the weightwhich can be added to completelysubmerge the vessel by increasing thedisplacement by the volume "H K AB". This volume is called the "re-serve buoyancy" and is necessary forstability and safety against sinkage.What is Meant by Reserve BuoyancyIn Fig. 10 the utility of reservebuoyancy is indicated. Assume that

the box-shaped vessel has two wallsor "bulkheads" (G M and FN) divid-ing it into three compartments, andthat the vessel floats at the waterline W L. Suppose that a hole ismade in the bottom of the centralcompartment so that sea water entersbetween the bulkheads. Before thisoccurred the volume of the hull (BCFG) between these bulkheads dis-placed a certain amount of water andthus helped to float the vessel orrather to support as much of the totalvessel's weight as would equal thewater displaced. When water en-tered the compartment the sectionbetween the bulkheads no longer af-forded buoyancy since the volume ofsea water originally displaced rushedback into the cavity. Meanwhile thevessel's weight has not changed andsince this weight exceeds the netamount of intact buoyancy represent-ed by the displaced volumes A B G Hplus C D E F, the vessel will sinkuntil the weight of water displacedagain equals the original amount.This sinkage is assumed to the waterline W' L'. During the sinkage thewater rose freely inside the damagedcompartment to the level M N and nobuoyancy could therefore be regainedin that compartment.

FIG. 9ILLUSTRATES RELATION' BETWEEN DRAFT AND DISPLACEMF.NTWhen sinkage has ceased, the vol-ume L M G H plus the volume N PF E equals the original volume A DE 11, and since by taking B C F Gfrom A D E H we get the same vol-umes as by taking L M B A andN P D C from the sum of L M G H

and N P E F, we see that the addedend displacements LMBA plus NPDC must equal B CFG.

Figuring Reduced FreeboardNotice that the original freeboard

"f" has been reduced to "{'". Th's,reduced freeboard is easy to calculatein the case of a box. For exampleassume that the vessel in Fig. 10 is100 feet long, 30 feet wide and 10feet deep. Suppose the bulkheadsG M and FN to be at a distance of40 feet from each end, or that thedistance between them (B C) is 20feet. If the draft (A H) is 5 feetbefore the bottom is punctured, whatwill be the new draft after the acci-dent to the central compartment?First calculate the volume of the orig-inal displacementA D E H = 100 X 30 X 5 cubic

feet = 15,000.15,000Then = 428 4/7 tons of salt

35water or15,000 = 416 2/3 tons of fresh water.

35Then when G F is punctured the

lost volume of displacement is B C FG = 20 X 30 X 5 = 3000 cubic feet.Therefore the amount of originaldisplacement remaining is15,000 3000 = 12,000 cubic feet =ABGH plus CDEF.The lost 3000 cubic feet must bereplaced by volumes LMBA plusN P D C which are each 40 feetlong and 30 feet wide but whose

heights L.\ are not known.Volume LMBA = 40 X 30 X(LA) feet; volume NPDC = 40X 30 X (LA) feet.Volume LMBA = 1200 X (LA)feet; volume N P D C = 1200 X (L A)feet.LMBA -f NPDC = 2 X 1200X LA feet = 2400 X LA' = 3000cubic feet.

300OLA ^ = 1J4 feet which is2400

the amount the vessel will sink. Thenew draft is 5 plus 154 = 6j4 feet.The Value of Transverse BulkheadsThe foregoing shows the value of

transverse bulkheads and also makesit clear that the volume above theoriginal water line W L and outsideof the damaged compartment (B CG F) must be greater than the lostbuoyancy (BCGF), for unless thiscan be regained in the undamagedends, the sinkage (LA) will be great-er than the freeboard and the vesselwill not float after the accident.When some external force inclinesa boat the conditions which exist inthe heeled-over position are shown inFig. 11. The water line when up-right was at W L and the displace-ment volume had the rectangularcross section R A S T. Point B isthe center of buoyancy when uprightand point G the center of gravityof the vessel and its contents. W' L'is the new water line when heeledover and it crosses the original waterline at point O.

An Analysis of StabilityObserve that the cross sectionN D S T of the underwater bedy hasbeen changed to the form of a trape-

zoid, whose center of gravity is atB'. This point is therefore the center

. ^jy'l U


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12 The Design cud Coiistnicfion of Power Work Boats

FIG. 11HOW EXTERNAL lOKCE CAUSES HEELED-OVER POSITIONof buoyancy when heeled over andwe see that a change in the form ofa vessel's underwater body causes ashift of the center of buoyancy.Now the force of buoyancy actsvertically upward through B' and isequal to the vessel's weight actingdownward through G, which point isnot changed in position. The twoparallel forces are a distance of G Zapart and are called a "couple". Theytend to rotate the vessel in a directionopposite to the motion of a clock'shands, or "counter clockwise", whichin Fig. 11 tends to return the vesselto the upright. The magnitude ofthis couple equals one of the forcestimes the lever arm "G Z". Let Wequal the vessel's weight (also thebuoyancy or displacement in poundsor tons). GZ is in feet so whenW multiplies it we have:

1^(E^^^^HE fore end of a vessel is aM C*^ ridge formed by the intersec-^ i tion of the side surfaces, the^^^ structure consisting of a barcalled the stem. This bar may be ofwood or of steel in conformation to thematerial composing the hull. Attachedto the stem are the side planking orplating, the longitudinal framing ofthe hull, the forward end of the keeland keelsons, and some of the ex-treme forward frames.Stem construction for wooden ves-sels is shown in Figs. 20, 21 and 22.

Fig. 20 is the stem of a wooden tugbetween 90 and 150 feet long. Thestem log is backed by an "apron",both timbers being fastened togetherwith through bolts having counter-sunk heads riveted over ring wash-ers. Where the longitudinals end andat the deck, these bolts extend throughheavy knees called "breasthooks".The lower ends of stem and apronare scarphed to the stem knee and itsbacking timbers (called the forwarddeadwood) as shown. In Fig. 22 thestem of a larger vessel, the deadwoodis heavier; while in Fig. 23, the stemof a large vessel (2S0 to 325 feetlong), the forefoot is formed by twoknees scarphed to the stem, apron,keel, keelsons and filling piece, thewhole being backed by deadwoodtimbers.

Fig. 21 is the stem of a small ves-sel or shallow draft one with modelbow. The stem and keel are con-nected by a natural crook knee, mean-ing one in which the grain followsa curve. These knees (formerly ofhackmatack but now frequently oflocust, oak or fir), are cut from tree

.Sfopwotar

FIG. 21STEM OF A SMALL POWIIRWORKBOAT

stumps, one arm of the knee beingin the lower extremity of the trunkand the other in one of the largemain roots diverging therefrom. Thesingle knee forefoot is applicable to..mail vessels only, being limited inuse by the maximum size of kneesavailable. It is unusual to obtain thesewith arms longer than 6 feet.

(A-A), (B-B) and (C-C) in Fig. 20are cross sections at various pointsin the stem structure. The hull plank-

frames are notched into the dead-wood as in section at frame (1),Fig. 23.The construction of a "spoon bow"for shallow draft vessels is as indicat-ed in Fig. 24. One or more heavy"bow timbers" extend across the for-ward hull end, being scarphed toreceive the deck, bottom and sideplanking. The trusses ordinarily builtinto the shallow hull for longitudinalstrength, terminate against the bow

;f,j,/--ia8"ffobfae/ Line,

/\-iA

FIG. 20STEM OF A WOODEN TUGing joins the stem and keel at arecess or "rabbet", the intersectionbetween outside of plank and side ofkeel or stem being the "rabbet line".

In large wooden vessels with "mod-el" or ship-shaped forms, the stemis arranged somewhat as in Fig. 23.Apron and stem terminate at theirlower ends in scarphs bolted to kneesand deadwood. The keelsons andkeel scarph into the after knee, whilethe space between end portions ofthese and the knee is fitted with afilling piece. The extreme forward

top waftr

Srop^o^^''FJG. 22STEM OF A LARGE VESSEL

250 FEET LONG19

timbers; while the space betweenthese timbers and the first beam andfloor, are fitted with filler pieces. Afiller is also fitted at the intersec-tion between upper and lower chords(if the dimension "d" is small enoughto bring this about).

Auxiliary sailing vessels are fittedwith "clipper stems" afifording amaximum outreach for the forestayswith increased jib areas. Fig. 25 indi-cates construction of the upper partin wooden clipper (or overhang)stems.Keels form the strong center line

girder connecting lower extremities ofstem and stern post. Since theirfunction is contribution of longitudinalstrength, it is essential that theirstructure be continuous. In woodenvessels this feature is particularlynecessary but is prohibited by limitedlengths in which timber is obtain-able. This in turn varies with kindof timber.Oak formerly was almost altogether

used in keels. Oregon fir now hasbecome popular, principally becauseof its large sizes, long lengths,strength and durability.


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20 The Design and Construction of Poiver Work BoatsWhen the vessel is of such size

that a continuous keel timber is un-obtainable, two or more lengths are"scarphed" together as shown in thelongitudinal section of Fig. 26. The"hook scarph" here shown is securely

Fig. 27. An intercostal filler is lilted Figs. 31 to 36 inclusive are variousbetween keel and keelsons while the types of sterns in wooden vessels,frames have no joint in the center An auxiliary schooner or large cargoline. The lower keelson is shown carrier (ISO to 300 feet long) maynotched over the frames. have an overhung transom stern

Fig. 28 is the keel and keelson of (^"'S- 31). The keel extends beyonda wooden tug with continuous trans- ''^^ rudder post, forming a lowerverse frames; while Fig. 29 is a step-bearing

for the rudder. Bothsimilar detail of boats 50 to SO feet ^'^rn and rudder posts mortice intolong. The keelson in the latter is '^e keel, the "shoe" between theirlower ends being reinforced by nat-

ural crook knees which form the lowerarch of the propeller aperture.The line of counter is formed by

a heavy "horn timber", morticed to

FIG. 23STEM OF A LARGE WOODENVESSEL

FIG. 24CONSTRUCTION OF SPOONfastened with countersunk head boltswith ends riveted over ring washers,the recesses at bolt ends being pluggedin white lead. (Fig. 26-a.)I'ig. 25 shows a cross section anda longitudinal section of the centerline hull bottom girder formed byconjugation of the keel and centerline "keelsons". The five keelsons(as large as 18 x 18 inches each) arebolted together horizontally and ver-tically, their scarphs being spacedwell apart to avoid excessive weaken-ing. Long vertical bolts (b) passfrom keelson through the doubleframes to the keel. Shorter tliroughIjolts connect keelsons to frames out-board of the keel. The false keelis spiked to the keel proper overthe metal hull sheathing and is read-ily detachable when worn.The extra heavy planks adjacentto the keel and called the "gar-boards" are sometimes rabbeted intothe keel (Figs. 27, 28 and 29) orthey may be fitted closely against thekeel as in Fig. 26. Where garboardsare of considerable thickness, theymay be edge bolted to the keel.At points where scarph joints crossthe rabbet throughout the stem, keeland stern, wooden plugs called "stop-waters" are fitted across the joint(Figs. 17 to 23 and Fig. 26). Theseprevent entrance of seawater throughthe joint into the hull.The keel of a wooden schooner,110 to 160 feet long, is shown in

long.directly on the keel, forming there-with a rabbet and having the framesbutted on the center line. Additionallongitudinal strength is contributedby the engine keelsons which arenotched over the deep transverse take the upper end of the stern postfloor timbers and extend as far fore and to permit passage of rudder postand aft as practicable. and stock. The forward end of hornShallow draft vessels may be as in timber extends into the hull and is

Fig. 30 or the keel may be of same securely bolted to the deadwood andshaft log, against which it terminates.Notice the way the beveled ends ofall timbers are cut to prevent featheredges. At its upper and after endthe horn timber is let into the knuckletimber (Fig. 31), or the rim logs(Fig. 32).The propeller shaft passes through

a hole cut in a "shaft log" whichhas a stuffing box at its inboard endand is morticed to the sternpost atits outer terminus. Great care mustbe observed in boring out the shaftlog, particularly if it is long, so thatalignment with machinery may result.Sometimes it is made in halves (sec-tion "A-A" Fig. 32), facilitating this.All such joints must be well coatedwith thick white or red lead andsecurely bolted. Shaft logs may belined with a lead sleeve bedded inwhite lead and flanged at the extremitiesunder flanges of stuffing box andstern bearings. Ordinary pipe may beused here and threaded into thefittings at its end, sufficient clear-ance about the shaft being providedto insure against binding.The frames whose lower ends con-verge at acute angles at the stern arelet into deadwood timbers and secure-ly through bolted. Abaft the stern-

FIG. 2.5-CLlI.pER STEM OK AUXH.- P^^* 'hey butt against the horn tim-lARY SAILING VESSEL her, which IS rabbeted to take the

I30W FOR SHALLOW DRAFT BOATSthickness as remainder of bottomplanking. The reduction in strengtliis justified by considerations of draftand is reimliursed by correspondingincrease of interior hull strengthen-ing.Drainage of bilge water in all these

types is effected through "limberholes" cut in the frames as shown.Galvanized "limber chains" pass con-

Transverse Sacfign l^onifudinal 5e,cticnFIG. 26CONSTRUCTION OF liOTTOM GIRDER OF L.\RGE WOODEN SHIP

tinuously thfough these holes so that hull plank ends as indicated in Fig. 31.when drawn back and forth the holes The upper end of rudder post iswill be cleared of clogging matter. securely bolted to the deck beams andThe "limber strakes" fitted in the forms the forward side of a watertightceiling of large vessels afiford access box or "rudder trunk" through whichto the limber holes. the rudder stock passes to the quad-


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Stem, Keel and Stern Design 21

rant or tiller. A stuffing box em-braces the stock at top of trunk un-der the "rudder support bearing"which carries the weight of the rudderThe trunk is large enough to permitunshipping the rudder.

~hrouc\W'&o\f'-FIG. 26aHOW KEEL BOLTS ARECOUNTERSUNKThe rudder blade is formed by

heavy timbers fitted as shown andedge bolted together. Metal strapsassist in tying them together and areformed into sockets at their forwardends. Hinge bolts or "pintles" fitinto these sockets or "gudgeons" andcorresponding ones on the rudder post,the gudgeons sometimes having me-tallic bushings. Notice that the rud-der stock extends in one piece tothe keel. Where this is impracticablethe two lengths should be securelyscarphed. Lugs called "stops" on therudder post should bear against sim-ilar ones on the rudder stock, pre-venting a rotation of more than 45degrees on each side of center line.Rudder chains, shackled to an eyeon the rudder blade are led to padeyes on each side of the stern andserve as emergency stops in event ofbreakdown.Between the knuckle and upper

deck, transom frames are fitted as inFig. 31, the transom planks extend-ing athwartships being fastened thereto. The outline of transom forms aknuckle and a heavy timber conformswith it, being scarphed to take theends of the hull and transom planks.The knuckle timber and rim logs(Fig. 31) form parts of this transommargin log.Tugs and power lighters have us-

ually but one deck and a semi-ellipticalC6,/m^^ , /Tee/sons

Tfobbe,f

FIG. 27KEEL OF A WOODENSCHOONERStern whose general construction isas heretofore described. In Fig. 32the main point of difference is at thedeck where heavy rim logs are shownand a guard timber is securely boltedto these. The rudder stock passes

through the deck and is covered by agrating upon which hawsers arestowed. Sometimes the quadrant isbelow decks. Sterns of this typeare common to tugs and lighters be-tween 50 and 150 feet long .

Full transom sterns (Fig. 33) arecommon to small craft of all descrip-tions up to 80 or 90 feet long. Thetransoms may be variously formed aspreviously described but the samegeneral construction applies for all ofthem. Keel, deadwood, shaft log andhorn timber have already been con-sidered, except that where a metalrudder is fitted the shoe is formedby a casting as shown.

Hecho/i

RabbtfFIG. 28KEEL OF A WOODEN TUGThe rudder stock passes through a

lead-lined opening in horn timber andbearing log. A natural crook kneeconnects horn timber keelson orstringer ends to transom framing.Cheek plates are sometimes fittedover the junction of shaft log anddeadwood with sternpost.The proper rudder areas for vari-ous small boats will be considered

under steering gear. In event ofbreakdown to this gear a spare tillermay be inserted through the deckplate shown in Fig. 33 and fitted overthe square rudder head.

/fe/5on5

FIG. 29KEEL OF A 50-FOOTWORKBOATTransom sterns properly formed

are desirable for the additional holdstorage space, the wider deck, thetendency to prevent squatting whenunder way and the facility of con-struction. They do not render avessel difficult to steer nor makeher uncomfortable in quartering seasunless they are extremely broad andflat underneath.Compromise sterns (Fig. 34) are

seldom fitted to commercial powerboats. They are similar in structureto the stem, having a central ridgeformed by the horn timber, a kneeand the stern log. The plankingscarphs to these timbers and care must

be observed that the plank ends fitproperly and are not too narrow.The flat iron shoe shown in Fig. 34 isnot recommended but is indicatedmerely as common in pleasure boats.Such a shoe affords little protectionto the propeller since it is liable todistortion on contact with submergedobstacles, in which case the ruddermay be thrown out of alignment ortwisted and jammed.Shallow draft sterns with stern-

wheels are as indicated in Fig. 2iz.The flat bottom planking rises toa transom whose lower edge is at ornear the water line. The hull is notpierced as in vessels formerly con-sidered but rudder stocks extendup to the house deck as shown.Bearings at the transom and housedecks support these stocks and f^etiller arms are linked together overthe house or "texas".Multiple rudders are necessary be-cause of the limited draft and un-wieldiness of the boxlike hull. Theforward upper edges of these ruddersare very close to the bottom planksso that obstructions cannot wedge

l*X^ russ

GorboaraFIG. 30KEEL OF SHALLOW DRAFTVESSELthemselves between rudder and hull.Details of construction will be consid-ered under steering gear.The stern wheels, whose details ofconstruction will be later taken up,are supported upon two or moreoverhung girders whose inboard endssecurely bolted through the maindeck to the longitudinal trusses inthe hold. If the continuous trussesdo not end under these girders it isnecessary to provide auxiliary trussesor other reinforcing. The extremeoutboard ends of wheel girders areconnected by a heavy transverse tim-ber and walkways are provided out-side of the outer girders to facilitateinspection and repairs to the wheels.Vibration is minimized by hog postsand tie rods as shown which form part

of the longitudinal strengthening trussabove the hull necessary in theseshallow hulled boats.The paddle wheels revolve in a

clockwise direction, dip of the bucketsbeing fixed by vessel's draft, but sel-dom exceeding 27 inches. The afterdeckhouse bulkhead is termed the"splash bulkhead" and is watertight.


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22 The Design and Constrnct'ion of Pozver Work Boats

FIG. 31-'i ho c ^tal 3e fceel-OVERHUNG TRANSOM STERN OF AUXILIARY SCHOONER

Fig. 37 ("a" and "b") are two crosssections at "A-A" of Fig. 36 for dif-ferent tunnel constructions. Two ormore propellers are necessary sincethe limited draft cuts down permis-sible diameter and the total thrustarea must therefore be distributed.The tunnel should be a smoothlyscooped out recess in the vessel's bot-tom and the propeller tips shouldfit into this with minimum practicableclearance (yi-inch if possible). Thehighest point of tunnel should notbe more than one-third the propellerdiameter above the water line andthe after end should just touch thewater line at the stern. If this isnot practicable, a vertically hingedflap should cover the after tunnel end,opening with the stream flow whengoing ahead. This is to insure goodbacking qualities, the water tilling

The wheel shaft bearings fitted oneach girder are bolted to timber pads.Wheel girders are designed as canti-levers to take the wheel weight but ahigh factor of safety must be em-ployed to allow for the vibrationalstresses. At the same time theseoverhung weights are not directly sup-ported by buoyancy so that care mustbe taken not to trim the vessel by thestern. In most cases it is necessaryto locate the engine and fuel tankswell forward to oflfset the sternweights.

Propeller-driven, shallow-draft boatsare very successful if properly de-signed. Their advantages over stern-wheel vessels are reduced machineryweights, less difficulty in obtainingproper trim, improved maneuveringqualities, greater free deck space andcompactness of hull appendages.Higher speed of the propeller permitsof lighter and better balanced machin-ery for the same power.

Fig. 36 is a longitudinal sectionthrough a wooden tunnel-stern vessel;

fcalojart tail

Full Transom 3rrRN^Sparc TiHc-r

FIG. 33TRANSOM STERN FOR SM.M.I. r.OAT WITH METAL RUDDER

FIG STERN OF TUG OR LIGHTER WITH SINGLE DECK AND GUARD TIMBER

^~F/af Iron ShoeFIG. 34COMPROMISE STERNS SELDOM USED ON WORKBOATS

the tunnel when flap is forced closedby astern motion.

Cross sections along the tunnelshould be circles with varying diame-ters and their upper points in thelongitudinal profile curve of tunnel.Workmanship in wooden tunnel

sterns must be of highest class, sincesmooth water flow is essential and leak-age is likely due t > complex struc-ture.

In Fig. 37-a the tunnel is merely awatertight box with arch beams towhici! is fastened a metal fairwatertop; 37-b has the tunnel formedby bottom planks which are cut andbent into place, calked and fastened toarch beams inside the hull.


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Stem, Keel and Stern Design 23

U U J U U U U U T"

Stern I I:^[,g^^:li3^l^

FIG. 35SHALLOW DRAFT STERN WITH STERN WHEEL'

^

A'

/UN hi EL SternFIG. 36LON'CITUniNAL SECTION OF WOODEN TUNNEL STERN BOAT

.3he,lf

Fromt

Bcyom Log

JECTION ThHOUGH TuNNLL 5 TERNSFIG. 37CROSS SECTIONS SHOWING DIFFERENT TUNNEL CONSTRUCTION


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24 The Design and Consintction of Power Work Boats

KAMCHATKAA SAILING VESSEL RECENTLY CONVERTED INTO AK AUXILIARY FOR USE AS A WHALER IN THEARCTIC OCEAN AND BERING SEA144 feet long by 31 feet beam by 15-foot depth. Fitted with a 300-horsepower MacIiUosh & Seymour diesel engine, which drives her

at r^^ knots loaded. Two au.xiliary engines, one 25 horsepower Burn-Oil, and a 20 horsepower gasoline engine installed.


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CHAPTER VIApplication of Steel Construction

long.

^TEEL construction as hereconsidered will be limited topractice in commercial ves-sels between SO and 250 feet

Bar stems are ordinarily fitted inthese and are scarphed to the platekeel or bar keel as in Fig. 38-a and b.The length of these scarphs is ninetimes the thickness of bar stem and keeland the scarph faces are machined tofit closely together (Fig. 38-6). Theshell plating is flanged to the stem andis connected thereto by through rivetswith countersunk heads. In small ves-sels a single row of rivets is used butin vessels more than 75 feet long tworows of zig-zag rivets are employed.When bar stems join a plate keel (Fig38-a) their lower ends are flattened outand riveted thereto (Section Frame 2).At one-twentieth of the vessel's length

from the stem a transverse watertightbulkhead extends from side to side andfrom keel to upper deck. This is the"forepeak" or "collision" bulkhead andthe space between it and the stem is the"forepeak".Deep transverse floor plates whose

upper edges are stiffened by the reverseframes, connect the lower ends of framesand are cut to permit passage of thecenter keelson plate and angles (Sec-tion Frame 2). Where longitudinal gir-der angles (called keelsons or stringers,

according as they are on the vessel'sbottom or sides), join at the stem, theyare connected by horizontal bracketplates or "breasthooks" which are con-nected to the hull plating between framesby short "shell clips" and have their

after edges stiffened by an angle. Largebreasthook and floor plates are piercedwith "lightening holes" cut from theleast affected part to reduce the weight.Limber holes drain the spaces betweenfloors (Section Frame 2).

FloorPIc;^^,?^'-iPlatcX

GorboardStroKc

Keelson Ro*6

i a^boordStrode.

"iSide BorKeel plote. Kee.1 Plo+c-(b) Co.)

FIG. 39THREE TYPES OF KEELS OF STEEL VESSELS

Keelson Or\Floors ,KcHon IS

2^/ Framef\ooK Thrc'Keels

FowMdl^Baf Ste-m

FIG. 38BAR STEMS AND METHOD OF SCARPHING

Keels of steel vessels are of threetypes: plate, bar and side bar (Fig. 39-a-b-c). Plate keels are common to largesteel vessels and to those of shallowdraft.Bar keels are used in tugs, power

lighters and in general for vessels upto 150 feet long.

Side bar keels are not extensively em-ployed due chiefly to the difficulty ofobtaining good rivet connections throughthe five thicknesses of metal (two gar-board plates, two keel bars and thecenter keelson plate).The Center Keelsons

Center keelsons form a girder withthe keel and their construction is affect-ed by the size of vessel together withthe method of making connection withtransverse "floor plates" which are apart of the framing and will be laterdiscussed. With respect to these

25


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26 The Design avd Construction of Poiver Work Boats

S+ringfrr AvT^le^

FIG. 43 CONSTRUCTIONOF OVERHUNG TRANSOMSTERNKnuckh

f?udd&rTrunKR'ljdde'f'Cou

Rudd&rFi-arn^-inch to J^-inchthick, depending upon the diameter.The size of an airport is expressedby the clear diameter of the glassand ranges from 6 inches in smallboats to 18 inches in large vessels.The rim in which the glass is fixed

is usually of polished brass or com-position metal, although galvanizedcast steel is sometimes used. Theglass is secured to the rim by acircular brass ring of quarter roundcross section which is held in placeby small machine screws. Cement isusually introduced between the glassand the rim to prevent leakage. Some-times a cast metal cover or "dead-light" is hinged over the glass rimon the inside of the vessel. Thisis usually hinged up and hooked tothe deck overhead. Its use is toclose the port hole in case the glassbecomes broken. A rubber gasket ispacked into a groove around the edgeof the deadlight cover and a similargasket is on the frame casting whichis riveted to the hull.

Circular ridges on the glass rimbear on these gaskets when the portis closed and when the cover isdown and prevent the entrance ofwater into the vessel. Three hingedeyebolts provided with butterfly nutsare equally spaced around the edgeof the port and the cover and swinginto lugs on the rim of these. Theports are held tight against the hullby screwing down on the nuts. Agasket is fitted between the airportframe and the hull on the outside,while a ring over this gasket fitssecurely to the frame. The framecasting passes from the inside ofthe inner sheathing to the outside ofthe hull planking or plating. Usuallya square wooden frame surrounds theairports on the inside of the hulland in large wooden vessels thisframe should be bevelled to affordmaximum light diffusion. This isbecause of the excessive thickness ofthe hull.

Air ports should be spaced midwaybetween the frames which should notbe cut in fitting the ports. Careshould be taken not to locate airports in the hull closer than two

and preferably three frame spacesapart.

Stock air ports are carried by mostship chandlers and can be selected fromtheir catalogs.Fixed ports or "side lights" admit

light only to spaces in the hull whichare near the water line or are placedin steel doors of deck houses. Thecircular glass is in a watertightfraiTie of bronze which is riveted orbolted to the hull and does not hingeopen.Air ports and fixed ports near the

hawse pipes are protected by steelbars or as will be studied under"anchor handling."

Wire Glass for WindozvsWindows of the drop or hinged

type are commonly fitted in deckhouses. Their advantage is in theincreased light and ventilation whichthey afford, although they are moreliable to breakage in rough seas.

This danger was formerly reducedby fitting wooden storm shutters out-side of the windows. The shutterscould be taken down and stowedaway. Since the introduction of"wired plate glass," shutters are notneeded if the panes are of this ma-terial. The glass is poured with awoven wire mesh in it, and actsin the same way as re-enforced con-crete. It will shatter under a directblow but does not fall out. Pilothouse doors should be fitted with wiredglass in all cases.Drop windows when open, fit into

a pocket between the inner and outerhouse sheathing. A recessed gripin the top of the sash should pro-ject above the sill so the window canbe raised. The sill may form ahinged cover over the window pocket,to present a pleasing appearance.The pocket is lined with sheet cop-per or galvanized sheet iron with adrain to the outer deck. The sash

FIO. 79CONSTIiUCTION OF niN(ilCI) WI.NIIOWS AND SKYM(;I1TS


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58 The Design and Construction of Pozver Work Boats

C. WASHINGTON COLYEB, ROCKAWAY BEACH EXCURSION BOATThis craft powered with a 6-cyl., 7^4 * 9" Automatic, carries 200 passengers and is operated by a captain

and two bands

slides in a groove in the sides of theframe and the bottom pushes outover a ridge. (Fig. 79-a). Pilothouse windows sometimes slide onvertical brass rods (Fig. 79-b). Win-dows with curved panes at housecorners are sometimes installed, butshould be avoided if possible becauseof the cost of the special panes andsash.Hinged windows (Fig. 79-c) have

the upper part of the .'ash in twosections hinged together. There isa deep channel at the top of theframe with clearance enough for vhesash to raise over the ridge on thesill before hinging open. A hookon the house beams keeps the win-dow open. Hinged windows aremostly fitted in the bunk cabins ofsmall vessels or in the after ena ofpilot houses which are raised abovethe deck house enough to permit thehelmsman to see astern.

Skylights of wood (Fig. 79-d) orsteel (Fig. 79-e) usually hinge up

and may be opened or closed fromwithin by means of a lifting gear.The covers are hinged at the centerand the frames must be watertight.

How Skylights Are FittedWooden skylights have a wooden

coaming bolted to the carlings andend beams of the skylight opening.Engine room skylights should beportable to permit removing machin-ery for shop repairs or renewal.The gabled skylight ends are con-nected at the tops by a heavy ridgetimber to which the hinges arescrewed. A drainage groove fits allaround the edge of the sashes toprevent drip into the cabin below.This groove drains to the deck at theends of ridge timber and at thesides of the sashes. Unless thelight panes are of wire glass it isnecesary to fit a metal grid overthem for protection againt breakageby falling objects. A canvas coveror "tarpaulin" fits completely over

MANHATTAN WITH A DECK LOADAnother Rocliaway Beach excursion boat with same power and capacity as Coli/er

the skylight and is lashed to thecoaming in heavy weather.

Steel skylights (Fig. 79-e) usuallyhave circular ports in the sash. Thesteel coaming is riveted to a platetop which is cut out in way of thehinged sashes, the opening being sur-rounded by an angle bar. The cagesof the sash are flanged downwardto minimize leakage and a rubberstrip or "gasket" extends around theedges. Light metal strips screwedto the sash secure the gasket. StiflF-ening angles or tee bars re-enforcethe coaming and tops of the sky-lights. The coaming is riveted to anangle bar and is clipped to the endsof deck beams Vv-hich have been cut.A margin plate surrounds the sky-light opening and is riveted to thebeams and the coaming angle. Insmall skylights through which it isnot necessary to remove machineryor fittings, the deck beams extendacross the opening to maintain thenecessary strength of the deck.

Skylight lifting gear (Fig. 79-e)may be of several diflferent types buta usual one consists of a verticalshaft having a handwheei which canbe turned from within the cabin.One or more bearings support thisshaft and its length varies accordingto the point from which the sky-light is desired to be opened. Aworm at the upper end of this ver-tical shaft actuates a worm wheelkeyed to a horizontal shaft. Theworm and wormwheel may or maynot be enclosed in a casing (Fig. 79-e).The horizontal shaft has one ormore levers keyed to it at one endand pinned to the lower end of acorresponding number of links asshown. The upper ends of the linksare pinned to bearings on the sky-light shutters so that rotation of thelevers by means of the worm, worm-wheel and horizontal shaft, will raiseor lower the skylight shutters. Thewormwheel acts as a lock on theworm for any amount of opening ofthe skylight.Some skylights have a slottedquadrant bar pinned to the shutteras in (Fig. 79-d). The slots in theouadrant engage a pin on the sky-light coaming and the shutter islifted from the deck above to thereouired amount of opening.Deck lights (Fig. 78-c and d) arefitted over compartments where ordi-nary airports, sidelights or skylightscannot be provided. They may havea cast bronze frame in which thecircular glass is cemented watertight(Fig. 78-c), the frame being screwedto the deck planks or plating. Aless desirable type has a thick prismof rectangular glass with bevelededges in thick white lead betweendeck planks (Fig. 78-d).


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CHAPTER XIIICompanionsHatchesRailsAwnings

COMPANIONSare openings in

the deck which afford accessto the compartments belowor above it. They may be in

the sides of the deck-house or may con-sist of a hut-like hood over a hatchwayhaving a ladder leading downward.

Fig. 80-a is a sliding companionhatch of wood. It consists of a smallhouse built upon an opening in thedeck. A carling at each side joinsthe deck beams at the ends of thehatch and the intermediate beamswhich were cut are notched into thecarlings. A coaming is bolted allaround the hatch to the deck beamsand carlings. The front of the com-panion has double doors which varyin height from 30 inches to 6 feet 6inches. If these doors do not affordfull headroom, the top of the com-panion slides back as shown to per-mit entrance.The sliding top may slope straight

back, traveling on girders as shownor it may be rounded as in Fig. 80-b.The minimum width of deck openingshould be 30 inches and the lengthvaries according to the slope of theladder so that the head of an aver-age man would not strike the deck ofthe opening in coming up.

Companion SlidesDeck houses and trunks of small

vessels where the height above thecoammg or sill is not sufficient topermit the fitting of doors which areof full headroom height (6 feet 6inches above the deck), have a com-panion slide or hinged hatch over thelow doors (Fig. 81-a and b). Theslide is the same, as for companionhatches and has brass metal stripsfastened to wooden guide pieces withcountersunk screws (Fig. 81-b). Thedoor closes against the front of thesliding top and is usually secured bya hasp and padlock. If the hatch ison a cambered deck and slides athwart-ship, drain holes are cut in theslide strips as shown. If the com-panion top is hinged, the constructionis the same except that the slides areomitted and hinges are fitted to thecover at the side away from the door.

It is also desirable to install hingedrods at the sides of the hinged cover

so that it may be opened to a degreeaffording headroom without throwingit completely back upon the deck.Companions of this type are difficultto screen properly and should beavoided if possible.

Fig. 80-b is a full height steel com-panion hatch with deadlights in thesides. The coaming plate and con-nections at the deck are the same asfor deck houses and a continuouscorner angle bar is riveted to thesides, front and back. The steel

door closes against this angle at thetop and sides while a reversed angleat the top of the coaming plate formsa sill. The side and back plates to-gether with the door are of from S.lto 10.2 pound plating (% to 54 inchthick) with single riveted "equal"angle bars and stiffencrs of the samethickness.Companion doors may be single,double or divided. The latter two

types are as in Fig. 81-c and d.They are resorted to where the pas-

I r-ane^erie SecTion. lon^ffuelina/

lf^* M WT^^P'M^MJ 'Ull

lb)

ir^' \-FIG. 80WOOD AND STEEL COMPANIONS

59


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60 The Design and Coiistrnction of Pozver Work Boats

^ra/r7 ha/e

3rass M \ I

Defa,7cf^Me

t:"^ Tar/âu/ffj'^.(k Lej

3echz.Woferf/ahT

iôoden Match. 7[)

y^ôr///^0

Pech 'Beam.

KIO. 81DETAIL CONSTliUCTION OF COMPANION SLIDES AND HATCHESsage into which they swing open isrestricted. The hinges and locksshould be extra heavy and arrange-ments should be made to hold thedoors open by brass hooks or byspring catches. Rubber topped buf-fers should be on all doors whichopen against interior or exteriorjoiner work having a fine finish.The deck immediately in front ofcompanion doors is subjected tosevere wear so that treads of hard-wood strips are fastened to the decksat this point. Sometimes cast brassor iron plates which are roughenedby a pattern or which have a cementor lead filling in grooves, are used inthe deck in front of doors.

Ilow Hatches Are ClassifiedHatches may be roughly classed aswatertight, non-watertight, flush or

raised. Watertight hatches are fittedover all compartments opening ontodecks exposed to the weather.Wooden hatches are difficult tokeep tight. They consist of a coam-

ing bolted to the carlings and beamsaround the deck opening. This coam-ing has a rabbet on its upper edgeand the hatch cover fits securely intoit. If the hatch is small the top maybe in one piece, usually rectangular,composed of tongue and groovedplanks with a rabbeted frame andshort beams. Hooks on the coamingengage eyes on the cover frame andclamp the hatch closed. Sometimeshinged hasps on the cover fit overstaples on the coaming, and pinsthrough the staple hold the coverdown. If the hatch is hinged, a pad-lock on one staple may be used andthe hooks also be fitted at the sides.(Fig. 81-e.)Large wooden watertight hatcheshave sectional covers on portable

beams resting in the notched andrabbeted upper coaming timber. Aheavy canvas tarpaulin is stretchedtightly over the closed hatch bymeans of an iron bar which is wedgedinto metal lugs on the coaming. (Fig81-f.)

Watertight steel hatches when smallare called "manholes" or "scuttles"and may open into tank compart-ments below decks as well as to theweather. Manholes to tanks whichare seldom entered should be boltedclosed as in Fig. 82-a. The openingshould not be less than 11 inches wideby IS inches long with circular ends.A forged channel or double anglering encloses the opening, the coverplate bolting on the upper flange asshown. A gasket of hemp or canvasfits between the cover and the coam-ing ring. The tank, bulkhead or deckplating which has been cut at themanhole, has a re-enforcing plate or"doublcr" riveted all around the open-ing to compensate for the loststrength.

Manholes of Various TypesManholes fitted with "strongbacks"

arc common to tank compartments.The elliptical manhole plate is in twothicknesses, the upper of which israrrower than the lower. The platesare riveted together and a gasket isfitted on the shoulder as shown inFig. 82-e. Two shoulder bolts areriveted through the cover plate and"strongback" bars fit over the screweder.ds of these bolts, extending acrossthe narrower dimension of the man-hole. Nuts over washers tighten thecover against a flanged manhole ring.Hinged manholes fitted with "dogs"

arc as shown in Fig. 82-c. They maybe square, round or elliptical and havea number of forged lugs which engagehinged bolts with wing nuts aroundtlicir edges. The hinges have an ovalslot on the pin to permit of tighten-ing the cover.This type of fastening is employed

for steel watertight or oiltighthatches with hinged covers. A platecoaming from 9 to 48 inches highsurrounds the hatch opening and hasa coaming angle at the deck. If thecoaming height exceeds 20 inches itis necessary to stiffen the plate withbrackets and angle clips. A rubbergasket at the upper edge of the coam-ing plate is clamped thereto by anangle or by a flat iron bar. Cast orforged steel lugs riveted to the coam-ing, attach the hinges and the ringbolts.

If the hatch is more than 24 inchessquare, the cover plate should bestrengthened by an angle around theedge. Hatches smaller than thisusually have a flat bar around theedge of the cover for strength.Hatches more than 48 inches squareshould have stiflfeners of angles orbulb angles across the cover at inter-vals of 24 inches.Deck scuttles are of cast steel or

composition metal, not less than 18


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CompanionsHatchesRailsAzvnings 61nor more than 24 inches in diameter.They consist of a flush ring casting,bolted or riveted to the deck plankingor plating and having a depressedcircular ridge on which a rubbergasket in the cover bears. The covervaries from J^ to 5^ inch in thick-ness, is roughened on the upper sur-face and has two hinged ring boltswhich lie flush in depressions and bymeans of which the cover may belifted. The cover is tightened againstthe ring casting on the deck by meansof six bolts with heads resemblinghorizontal cams, or else by a centralbolt which screws into a bossing ona hinged strongback under the scuttle.A special wrench is provided totighten the scuttle fastening bolts.When the cover is removed a castiron grating fits into the opening andaflords ventilation. This grating maystow in three clips on a bulkheadnear the scuttle or may rest in de-pressed lugs under the cover whenthe scuttle is closed.

Steel cargo hatches usually havewooden covers which rest on portablebeams in the hatch opening. Atarpaulin is stretched over the top ofthe hatch in the manner described forwooden hatches.Ladders and stairways may be of

metal or of wood and are vertical orinclined. Inclined ladders should notextend athwartships in vessels forrough water service, unless this ar-rangement cannot be avoided. Thisis because of the danger of fallingdown them when the vessel is rolling.In passengers' living spaces stairwaysare usually built with a slope of 45degrees and with good wide treadsand ornamental railings. These some-times turn from two athwartship sec-tions to a "grand stairway" openingin the saloon. Curved stairways arenot recommended for use on vessels,it being better to change the direc-tion of the stairs by i

the design and construction of power workboats

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