ELEMENTS OF YACHT DESIGN NORMAN L. SKENE, S.B. BY

PHOTO BY EDWIN LEVICK 50-Footers Mystic andAT Iroquois CLOSE II QUARTERSI DODD, MEAD & COMPANY NEW YORK 1945 CHAPTER XVI rest,frictional yet there resistant.. is -. Rudders, struts, skid fln, propeller hubs, water i appreciable amount of wetted surface with its FIFTYovei' the surface of the wateravailable, the basic idea of a hull with a bottom formedyears to before engines of high power THE HYDROPLANE instead of going through it was invented and light weight were skim andresistance.scoops,to mustP perpendicular bauers be the andpoint toother aboutInthe the bottom.hull whichdiagram, projections, The the thepointboat water balancesPeach is pressure the adds center when to is of shownlifted. pressure Ifacting upward from A the total orandbeganhighthat skimming reinvented no enough about boat hull 1910.couic! ato dozen wereplane. float times. The the ideapowerEarly is attemptsoldrequired but its toto practicaldrive unsuccessful because engines were so heavy build a hydroplane lier at a speed application ing"willthis center rise.or leaping One is too of motion farthe aft,commonest caused the bow by willfaults the drop;weight of a if hydroplane tooof the far boat,forward, is the a "porpois- thrustthe bow of resistancewave-makingpercentage increases of ofthe the total hullsoIt resistanceliasrapidiy of beennormal at shown tohigh form. a speed in It previoushas for been a chapters boat's motion is caused by the how an ever increasing small increase in shown howdefInitely the lim- speeditedplane and causesthat wheredepend speeds the the onwhole of l)ottomthe boats lengths.t)Oat of is the toso riseThis displacementformed b does dily that notand forward holdtypeto be aretrue supported bymotion theof the at highboat. of the hyclro- FIG. 150 surfacesdesignerAlldynamic major andmustreaction forces rounded think are between entirelyof shapes Allthem ideasthe dynamic as which water such. of stability inandmightOn character the ascause bottom figured for normal forms are and the hydroplanesuctions must be of the boat,null ali and void. reactions another.thenormalnorhe screw determined can Unfortunately, upward itand be thegiven by thrust lift a by simpleof theof anythe the actual planesinspection plane location beingis the of improperlyrsìiltant theof the lines point of of many relatedthe of lifthydroplane, elementary cannotone to mathematical formula known today. This variousisandavoided. additionflowcompletely of wateraround forms In thereother leaving planingofa body isresistancewords another edges inon thethe the and designercleanlypreviouslywater. surface important When and mustof mentioned thesharply the thinkfactor. water resistance of impacts,are rather than thinkis analyzed, of all the of a hull whichfound and in paradoxofmanywaterpressures the haspointcases, that strongand where thethe suctions. downward actualcenter the keel C.G. Evenof touches thesuctions of a resultant true tlìe insteadplane water, upward of thus lifts pressure creating at onthe thecurious bot- the whole boat may he carried ahead moving at an angle to the the after end. In componenteddyface.In addition,resistanceThe displaced of therethebehind perpendicularwater isThe thea horizontal createshydroplaneshafts, struts,wave-making pressure resistance has rudders frictional on and otherresistance on her actual which is the horizontalresistancethe and inclined there is planing appendages.wetted sur- cessfulsuspicionexaggeratewatertom of surface. thehydroplane. ofboat this upward An iscondition. aheadupward curvature of curve Bottomthe point at thelines, of afterstern contact therefore, if the of thehull is to be a suc- end of the bottom tends to should avoid anybottom with the ofsurfacelliRh the water ofthe the boat iii bottom. theplanes, directionFig. there 1 50mustshown represents be by water the a arrow.simple hydroplane moving 210 displaced with consequent along the surfaceNo matter how ponenofponents, the boatt equal AB thus which to actingthe istotalThe horizontalas annormal added and upward resistance, opposed pressure andto BP, AP a verticalcan be resolvedcorn- into two com- weight of the boat. the forward motion anglegiven decreases.value of BP, At equalfirst1'Ioili sight, to uR;the it weight might appear6f the bt, that AB to decreasesmake t' as the . .. .. , added mathematical relation between a motor kiven boat and a towed r------o'rchitects of wide experience on displacement ------. increasessistancealthoughtheresistance most decrease efficientbothClue very thisto small, the as hydroplane.horizontal theadded by angle keeping amount componento This decreases, the of however, anglesurface and Othe required small,the frictionalis notwave would the for making resistance truthlifting produce and, re-the whosep1p_designhydroplanes.boatsmodel.been have accuratelyManyperformance, been is The nav2to misted make safestdetermined. chacteistici aby proceduremodel misinterpretation This of a to modelknown follow can andof in modelbe developingsuccessful used tank as a resultsboat, acheck hydro- one on on a eed;61er, and weight have planeoncreateforboat successful a at planelessthe the leastrather small sui hydroplanes.possible face thanangle. greaterthat resistance, By thäilo mathematicalIt if is any advisable whichshötild departure agrees treatment beto makefromipproximately well the withtheit canconventional angles be shown 2'° 'used to angle of tile / model embodying any proposed design or imrovément. But even anglegivespeedperiments is comparative orcontemplated. the on action small resultsat modelspeedLittle only, of hydroplanes accuratea andfull sizer!then information only boat.as to if Model thecarefully actual can tests be interpreted. resistance,can obtained and do from model tank ex- asourmentsTo practical attemptknowledge, as is done toresultsices divide not withof aretheat the ships all concerned,model total practical and resistanceand their boat models have of a is,thehydroplane in same the presentratio into asstate itsthe ele- displacements and is definitelyitcan be assumed misleading. that As the far resist- of frictionalofsistance,the the calculatedtwo. resistance requiresAny attempt frictional an and accurate theto separateresistance wave-making estimate the of ofresistance the theresistance, modelarea ofof from the theby modelsubtractingmodel the total in con- re- into FIG. ISt resistancestionalmodelstact with resistance and the vary in water. determining directlyis far The greater asUnder error the than displacementsproper inaverage themaking errorcoefficients conditions, involvedsuch at corresponding estimates to the inlise assumingsurface for on the tension of water is a constant. speeds. small fric-that modelthistowed must of in a be successfultile used tank with at boat,speeds caution a recordcorresponding for breakingcases llave to the occurred champion, could not be official speeds which where the ThisSurfacethisthin constant size glassy tension is exactlydetermines sheet. will theOnhold thesame,the the size boat, small both of this drops bow for wave wavethewhich willmodel of water abreak model and will up for together into the in a form anddrops or boat. the notaticaltile tank boatavailable results is ownedhad if actuallytheyto andthe could operatedprivate made.Models he towed naval eight inarchitect afeet, high ten speed feet, or twelve feet in length by the United States Government, it-is and, until the services of tank. Although such continuewould to give be prac-a foundwhitetotalamountboat spray. inweight,and the of may boat.Onwetted is cause theanother surfacemodel, aThe suction force propellertileand wilich glassy whichthe resistance causesthrust, bowentirely wave thetoo, of changes model willbeing adhere and athe fairly boat to tolarge act percentage of the model from that trim, the the andthaninhitthis careful theand tankon perfect miss any canexperimental ruletruly be tuning ofobtained, scientific thumb up changes of affair hydroplanedesign the inwheremotor thebased bottomsuccess anddesign on onexact will depends morepropellerof the ori actualsmall experiments boat and knowledge. 1. )'C1i1L It is usually unsafe to have the center o! gravity over b per cent ot tte 4.3.2. 5.SingleInverted Three Step. point "V" hydroplaneshydroplanes. or 'Iultiple-step or "shingled" with two points forward.aft. hyciroplanes. "Sea Sleds." feetcenterwateran of inch. line theof gravity lengtl.bottomThis hook, canshow gohowever, a slight the boat abaft the fore end of thEwa ter somewhat further aft if the last two or three has otherdownward disadvantages hook andof perhaps is not con- a quarter of Ìire. The usuallythenoted after that shows third the bottoma of slight the lineslengthamountIn Fig. carry are of 151 is shown a 6. Hydrofoils. modern stepless hydroplane. It concavityback sosttaíhTliñes. that the buttocks In section, for at least the "V" this amount depending will be iI ducive to safety in a sea nor to FIGsafety 152if possible. when making high speed turns A MODERN STEPLESS 1-IVDROPLANE general way, the steeper andinadditionhas is,contact been therefore, tothe with upward subject thea he waterpressures ofavoidedThe much isexact ori action of the water on subjected to a downwarddiscussion. suction. It is It conceded is today that,the bottom, athe great bottoni part of of a thestepless area hydroplane for in oneonconcave.the the side'or "V.:) "V"steepness angle, theIn veryothei the flatat greater "V's" theit of the angle of the "V." In a high speedunless this is corrected is uiìnecessary tendencyto use much for or the even boat any to heel over to by concaving ninabouts invertedexcellentformsthis reason in laps whichresults that of anthe thein attempt many steplessplankingVarious cases. is type createdforms These of maylongitudinal steps macle to avoid these suctions. is less efficient than any of the other byhave starting been the used lapstrake and have bottom shown be nothing more than the bynormalnearlyandthan high in asthemany boatspeed efficient more form,high is radical meant as speed it the Thisis hydroplanes. aothera farstepless types type is exemplified cruisers.speed-Ieiìgth For extreme ratiospeed, of itapproximatelybetter boat at low and medium in all modernIts greatest high speed faultbut, at since high itspeed is much closer to is nowhere speeds 10 or andthe inshownplanking steptoward inor Fig.at"shingled" the thé 1keel 52.chine asThese theyinsteadBy planks goan ofeasy are transition from hydroplane is arrived at. In place of aft.the stepless hydroplane,the keel.the multiple- A section of such usuallya boat is wide at the bow and taper the smooth unlessthèin.is broken Forit was up many moreinto years, a than number twoit was ofinches consideredshort deep. planes Modern that with sinai!experir. no step ws effective steps behind its, how- shownworkedafterLagarto,Many year, inaout. hydroplane lilillOUS Fig. is without 154, ShlIlIgICU designeris doubt Thean efficient singleiiyuropiaiie theclaim most step forform WIIACILeflcientittype an when efficiencyof hydroplane, hullwon properly hICof greaterthis I.o1U designed. typeof t.up thanwhich ever year that a typical example is ever, have shown that a step even live-eighths of an inch deep is A LONGITUDINALLY STEPPED hYDROPLANE an multiple-stepGoldbehindeffective Cup the step understep. planes if Manyproperlythe byrules of the theinvented addition voguestepless fromof hydroplanes planes 1923 which raced so that air has a chance to get in on the bottom appliedto 1933 in were altered to for tue FIG. 1S4 FIG. 153 Cc44L -- -t-_ thebell'sitof must any single Bluebird, other. be step noted This, type. and that however,the the famous world's is A'Iissa matterrecord Americas ofholder, opinion of Sir Gar but Malcolm Wood in all arefairness Camp- all of dicatedshownPointsplanethe form in and of ofFig. of Fig. shinglesthe wedges153 aftermost151. which at Theor keel "shingles." shows planeangles and shinglesslsouiilchine are Usually slightly should be applied the four touchexaggeratedsteepest. to the straight stepless The formultiple-lines hydro- clarity. or five steps are used as as in- thetogreatbeingangle place whole variation thanapproximately it boata the little isaboutafter possibleabaft plane, five three-fourths amidships In inper thea centsingle locationamount and of to stepits to one oflengthhave hydroplane, the differenceand thestep abaft one-half center but the initthe of step.is planedegrees. customaryforwardgravity This angle ofisA plane should have less inchparticularlytheseaworthinessstep on running hydroplane, Delphine the of angles tue toIV, although theboat. a ofmultiple-stepstepless Loweringthe notafterniost type.highly the hydroplane, A afterplane, eflicient,slight step haschange onlyis,changes in one-eighth ingeneral, plane her from angles,next of in a marked effect on an a eitheratnot thethe a hardbowstern.too steep andup If into thefast an bowtheangle rule, air liftsSingle onlyor and thebadly athen step C.G.guide in slamhydroplanes isporpoising, to too goodit fardown aft.practice. sometimestheagain, If thereforward or is may porpoisea planetendency jump has badly.out They may throw plane is too great or tuìe C.G. is too far forward. It will be noted in the wheremoderatenormalamidships it displacement will speedsand plane. thL and wide There Themustform transom, formis carrythat usually itof highis has t' a power to single step hydroplane with the notch cut such a radical departure fromsharplyexcessive the defined resistance speed at atlow which and drive it UI) to a point out planingpartiallyenginefor roughis throttle definitely closed water but and workestablished. after high A isplaning speed formthe inverted To of has hydrplane of unusual type maintained. beenreach attained this point the may throttle require may full be _patentedwhich has many Hickman advantages "Sea "EL LAGARTO" Sled." This type is shown in Fig. FIG 155 155. The inverted "V" runs almost Thisportantassistthe hulllength in gatherscompetitions, lifting of the underit. boat, Although itselfmanywhile the theit has bow never wave large boats of thisSled" form shown have beenindeck the photographoutline is practically is, a been seen in any of the itn- and utilizes this wave to rectangle. frombuilt DELPHINE IV" forbetterQnaweightofa specialweight-speed than purposes. 46 statute 34 Thepounds miles "Sea toan thehour. standpoint, one of the most efficient horsepower, the officialSea speed Sled" was is excellent. Due to hulls ever built. the sectionpreventwaterflared shown doesfrom water notaof comparatively catchingthe touch these flared bottom single step hydroplane that the the chine and capsizing the flat and narrow bottom. At top sides and in turning they sides areboat liberally as she skids speed, / enginehydroplane.invertedform ofand the "V"it bow,basa The ia therebasictrueIn planingis Theideaa followinglittle latest of the hull hydroplane sea1 the action development of the" decided planing point. tendency to yaw as the stern lifts. three-point hydroplanerequiring is tois form aoften light termed and powerful a "three-point" The watertiletends whichhave to give far has lessgreat not lift beenefficiency, for disturhed a given since amount by planes anyDOLLOIII planeof which SU 11141. run i' 1.11Cl C ai L LL 'L- wetted suuace than ahead of it. This listurbed form.hasthethree Bluebird,anIt pointis official this hydroplane formSir record which of isapproximately promises considerably to reich 130 Dcucr evenmiles tiiaii greater an hour.uiai ut ally uttici ilcolni Campbell's single step hydroplane, which speeds than pointplanesthree-point aft passing is shown hydroplane through in Fig. undisturbedhaving 156. two In the points water. 225 of cubic Thesupport general inch forward idea and of onea hydroplane is anythisthesupported wing othertype ofof form.by anhydroplane small airplane. This, submerged Thehowever, The an sixth efficiency proponents hydrofoilsisclass open of tobettergliding of shaped the than hydrofoilhull canis that be idea infound which the weight of discussion as the "Sea Sled" Oil the principle of claim forthe boat with

class, all successful hulls today are of this type. Official 1iG. 156 records of ofbeenand the the reported hydrofoil three-point for are anyhydroplane below hydrofoils. the havewater, Since shown it has the efficiencies no min inherent supporting as A HICKMAN "SEA SLED stability of itshigh as have surfaces bemade.inchesbetter considered thanpiston 72 displacement little miles "V" anFor bottom hour, a developing single with hulls, screw a shouldmotor 165 hydroplane, horse beof forward.not power, overthe two If points of support, which may have been225 cubic the boatthe two sufficientestseries,own. and Stability one lowest to above lift atfoils to speedthe the are other, surface; undermustSeveral so be thethat but water partiallyat stability the and highest successfulis none speeds too craftonly good have at best. been built on the gained by having the foils arranged in they cannot have an area the small-hydrofoil benotforward.supportinghas near tootwin far the screvvs,In abaftforward ordersingleplanes the toSorne centerofattwo get themthe supporting stability,advantage plane.after if they end the aresurfaces isof C.G.toaft. the be In of boatgained no the case with whole by themaking boatshould when they are forward, and should the weight single plane be Thetypester.airidea greatest propellerNo but in hydrofoil any it hydrofoildoes importantand notairhas propelled successes lendas competitions. yet itself ever crafthave tocompeted use arebeen beyondof attained the under-water the with scope the of use successfully with the other thispropeller. chap- of an ofdli beproximationalinosithe obtained various ill ttìSSl formsfromto l)IC the 1)1an ofprobable empiricalUUi(::Uihydroplanes speedLU formula LdÍLUI1LL byof anya wellwhich scientific LII. is as designed hydroplane may follows: meti '. Ari ap- sJ)eed.createdmuchit is, as less itThis by does thanshafts, may giv appears struts, at rudders, first glance skid as fins, it takes and othercare of underwater the resistance de- oear ton beadvantage faulty mathematics to large boats. and The to some error, extent however, is ofrootin pounds,which of this will byweight bethe given actualper horse later,Divide horse powerby powerthe the totalandsquare of actualthe root motor. runningof weight of boat, then divide a coefficient, values thecomplete weight with per crew,horseObtain the square correcthydroplanesappendages.differenttails which as from the cause isAt most that available, the the calculated complicatedpresent resistance this time, fromsimple calculations. of when modelthe formula actualno tests high is,hydroplane on speed in a practice,hull without to asbe nearly these tank for testing quite

L aspo\'et a formula: to obtain the probable speed in statute 1wC FOPS -U S A THREE-POINT hyDROPLANE miles an hour. Expressed mateinWhere runningstatute values: C ismiles condition, the coefficient,per hour. P Forthe This Wactualordinary is coefficient the brake total stepless horse weight lias hydroplanes, power,the in following pounds and of such approxi-the asboat high speed runabouts, Np Sitie speed data250.most210.equalsC equals Forare Valuesefficient. 190 not"Sea 180 to available.fpr Sleds,"205.to For hydrofoils185. Singlesmall C For is 220 three-pointstepmultiple-step cannot for hydroplanes small be hydroplanes,included sleds or shingled ofto good 270in this forC design,hydroplanes, formulathe C as is about 240 to largest and equals the C