Sailing Aerodynamics

7/29/2019 Sailing Aerodynamics

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etoassemblewillbe,

men.Somepartsmight

maticsbutwhentheseare

arytrigonometrywhichevery-

ederivedperformance

chinterestusmostdeeply.

givensothat,notonlymy

eobtainedforotheraerofoils

heorythanisnecessary

andthebasicfiguresonwhich

ndtheorymaybeobtained

erestedshouldrefer.

Nonehavebeen

terested,iftheyshould

nyonedoingsuchdevelop-

hicharementionedin

ars,itiscertainthatseveral

tationofotheraspectsisnot

rticularfeatureofthesubject

egladif theywouldletme


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anmainsail..83

g....98

110

ewind....116

eeze..120


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esbyaprocessof

sorinflatedskinby

aybethoughtofas

thatindividualityproduced

isway,afreshmethodof

fromboattoboat,ifitin-

edlogcanoe,thebundle

dintothebeautifulsailing

thetwentiethcenturyorthe

ontheNileandrivers

sofprogressoccurredin

ries,especiallyNorwayand

s,shelteredwaterin

sscouldbeneglected.

tchesofshelteredwater

pesofsailingboatsand

helteredwatersoevolution

nchstudiedandtheorised

pwrightsoftheeighteenth

ohercannonorherability

wasabletomasterthe

y.Thesailsofboatsdid

hthesquarerigandthefore

wasinitsprimeandthe

ofgenerationsofmen

oduceforagivenpurpose

bemadewithdevices,

omerecentexperiments

ntwisted.Tobepractical

wasquitecapableofdriving

anrig.Thenextstepin


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ngernecessarytotryevery

anreplaceavastamount

ebeenconcluded,apractical

tisimpossibletoallowfor

n,too,thereisthefactorof

onlypracticablebutsafeto

ynamicswillthereforegive

ngonaboatand,inthisway,

oidedsuchasthetrialofa

maerodynamicsasapplied

ntheliftwhichhisaeroplane

ogivehisaeroplanespeed

gsofanaeroplaneare

espondtothetwofactorsin

ilyfunctionsof.thewings

nterestedintheforcewhich

vetheyachtsideways,pro-

heboataswellasbeing

ofasailingboathastobe

withoutslowingtheboat

eadequatelybalanced.These

hanextentthathisworkis

soneswhichhaveproved

orcesisnotpossible.

ttlehelpfromother

tenseemstohaveaccepted

ofaboatintoliftanddrag,

ne.Amoment'sthoughtwill,

selessinthecaseofyachts

forcewhichistheresul-

pushes,actingonthesails

slogicallytobemade,not

conceptionwhichhas

tobemade.

selfisaforce.That,

esaforcebyitsmotion

object.

udyistheresultof

theperiodbefore1914.

seemalittleoddtillone

umofthickness.Thispro-

rriedout.Theseexperiments


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tisbythesefiguresthat

sofgraphswillrender

ncehowthevariousfactors

resentationofthegraphs

ficult.Thisproblemis

eaeroplaneatall.Ameasure

heratioofthespeedofthe

heeffectreasonably.This

rawntogiveanabsolute

tfromthetruewind,notthe

realwindisthesameasthe

bedrawnforallspeedratios

arule,togivethetwo

oatssailandcalculateall

guresforaspeedratio

.Instrongwinds,aboat

eedratioapproaches0.In

atwhichthewindisgoing

notmeanthatourcurves

correctedforthis.Aboat

nd,wouldhaveacurveof

lyassociatewithlightwinds.

lsshouldbegivenfor

finitionscanbegiven

testpossiblethrustper

measured.Thesecondis

fromthewind,theoverlaps

nofgreatestpossible

omentat40 fromthewind,

ratiosails(aspectratiois

havegreatersailareathanthe

ouldbeless.Onlytwoof

reaisartificialandvariable

eedfor.Itwillnotbecon-

ependsontheratio

ate.

nmodelaerofoilsofwhich

yyears.Presentdaytests

orourpurposesthanthey

whichstatesthatforaero-

rasthemodelandproduce


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allangletoitsdirection

ingatauniform

directionorspeed.

ctionandreactionareequal

atshowninFig.1will

heairasitflowsby.Fig.2

andfromitrepresentthe

gthsofthearrowsshowing

straightlineandsono

upwards,fromtheweather

toweather,bothaboveand

ddownwardssoaforce

nsforthenegativepressure

vepressurerightontothe

ureofthepathoftheair


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edwithasmalleddyonthe

hecauseoftheshivering

cursexplainswhyahome-

windward,muchtomyamaze-

hattheleechstillcurled.

worseforitsunusualleech.

hsplitflaps,itispossible

ailinlightwinds.

ositiveandnegative

uniformarchi.e.,itwasan

egreatestdistanceofthe

mentsweretakeninawind

lbutone.A pressure

yatube,thewindflowwas

corded.Similarly,the

ramistheresultofsuch

agramshowsisthatthenega-

aterthanthepositive

arineEngineersin

carriedoutbyWarnerand

ermudianrigwasfound

enclosehauled,45%ona

tdesirabletohaveas

nourBermudianrig,

elythefore10%ofthebreadth

enegativepressureonthe-J

mtheseeddieswas18%

scausedwhenrunning.

ail.Fig.4isadiagram


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laraerofoilis2.66fora wing

rflap.Thisfiguretakesinto

einuse.Fig.6.is adiagram

hisfigure.Thecoefficient

kingthediameterareafor

heyimprovetheairflow

atthebreakawayatthestall

tthatoneaerofoilgiving

nsityofairandangleofattack

This,toacertainextent,

hat,ifafewsmallaero-

thanasingleone,verymany

orcestill.Thefallacylies

ivedfromanareathroughwhich

sisalsothefallacyofthe

boatswhichareheard

sionsonly.However,

differentlyatdifferentplaces

asseenfromeachside.

thecentrelineofsuchan

dge.Onthewindward

omthecentreline.Onthe

amtowardsthecentreline.

eathertotheleesideatboth

.Thecombinationofall


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nouilliin1783showingthat

eandviceversa.Thus,the

aerofoilandincreasedover

ressuredoesnotmeanthat

ssurereferredtoisthe

namicpressure^Ahomely

naerofoil,atleastpartially,

abasinofgranulatedsugar

therewouldbepositive

dbenegativepressure.^

ssurefromtheairto

rabledistancefromit,not

rofoil,thewindisspeeded

awayfromtheaerofoil.

inetostreamlinetillitis

othesurfaceisthelocal

tionoftheair.

faceofanaerofoilacts

tof asailisplacedso

ckwardcomponent,thatpart

ofasailtodrawbackwards,

artsinwhichcaseanadvantage

hthisismostlypro-

sproducedasfollows.The

es.Outsideofthisair,the

awayfromthesurface,the

reaofslipisknownasthe


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fsomeoftheboatsofthe

veincidenceacceptedatthe

sentdaysails,thegreatest

enceitwillstandi.e.,with

forwardcomponentof

heluffjustlifting.The

downwindandhencehasless

ed.

cidencecanbeaccepted

uldbecomparedwith

beunderstood.The

bstantiallythesameasin

tdrawing,isalsojustatthe

esent.Sailsoflowaspect

ecause,thoughtheforce

ultsinalessfavourableforward

ulloftheboatandthe

heairrisesattheweather

de.Itacquiresnogreat

ction.Theremustbesome

ies,itisofnogreatvalue.

fthegreatestpractical

eboomeddy.Thiseddyis

sthesailsthecharacteristicsof

lainedmoreclearlyby

acedincontactwiththewater.

herewouldbenoboomeddy

iraspectratio.Inactual

thewindandthereisthe

timated,thoughIknowof

ofapparentaspectratioasa

youryacht,therefore,you

oduceanapproximatevalue

erofoilsofdifferentshapes.


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EFFICIENT

hesquareoftheapparent

owever,whichoccursas

ichbecomesmarkedatwind

chisunfavourable,causes

mofthesailstobenecessary

er.

aerofoilbydividing

dthesquareofthewindspeed,

reaoradensity.Itis non-

icforceorCr.Thisco-


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sboththesetoaltergiving

nbytheracingflagandwhose

arried.Wewillstartby

dafterwardsseehowthey

angleoftheboatfromthe

dward.Theapparent

namicforce(R).Thisforce

ward,T,thethrust,andthe

.Thethrustforceisless

ionismuchgreaterthanthe

replateorkeelandsotheboat

taforcethoughitis stated

eddragbeseparately

heyshouldmerelybein-

producetheresultantaero-

odynamicforce.WA

whichtheaerodynamic

hedirectioninwhichthe

nd.TheangleABCisa right

odynamicforce.The


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henthedriveona boatis

ntsofthrustplottedagainst

otedthattheinclination

extractedfromEiffel's

winda,isalsothegraph

oatisstationary,because,

havenoforwardspeedand


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nglesoftherealwind.

ebeenexaminingforaspeed

ntsofthrustforarec-

dagainstw,theangleofthe

g.17withathirdgraph

uesofthecoefficientsof

ooutsidecurves,nearerto

oatisgoingslowlyrelative

edratioof1inlightwinds,

d.FromFig.17,itwillbe

ththerealwindjustbefore

ainedwiththerealwind

iththerealwindabout13

cularaerofoilattheaspect

heBermudianrigare,

swhichinfluencethe

wind.

seoftheboatandsplitup

.Wehaveassumedthatthe

hatwhichgivesthegreatest

orswhichaltertheCf

boat,sowestillhavethree,

foilsforourboats,sowhat

courseoftheboatforspeed

thenbeinapositiontoselect

seasyaspossible,certain

haerofoilforthevarious

rmanceisgivenbythe

of45 with5 of leeway.

thengreatest.Itsvalue

reshavebeenextracted

urealonethatthe


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,aswillbeshown

sotheCsf>sof little

entheaerodynamic

dered.

measure,afigure

aximumspeed

aisameasure

ditionsaswillbe

proportionaltothe

edisthenproportional

thecourseatwhich

closehauled.

goingtoextract

fwetakeasour

thalargesideforce

compensate.The

aterbutitmaybe

multipliedsothat

sailofaspectratio

multipliedbythe

minedforarectangular

performancefiguresare


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hoftheboat,andwhoseyard

nbe given.The

esixorsevenmasts,each

beenstated,werebetter

erenotsogood.The

ps,withtheirbottoms

gwasabletogivethem.

pfortheschooner's

anoeofthePacificislands.

ind,theapparentwindmust

ewindedrighadtobedevel-

tiosaileithertriangularor

dtrailingedges.Itishard

fahull,especiallyif

s.Athing,amixtureof

becalledahydrofoilbecause

lledaboatbecauseithas

snotasimpleboatbecause

eway.Moreover,thewhole

ewateratanangletothe

ssinlightwindsaswillbe

parts:theseareskin

omeserioustilltheboat

uarerootofitswaterline

etoskinfrictionwhich,

quareofthespeedofthe

asthesquareofthespeed

ximatelyproportionaltothe

smeansthatwhenthe

boatwillgoslightlymore

avemakingresistance

dincreases,getslessandthe

mesthesquarerootofits

enttypesand,ofcourse,

waterand"Plane."

utofplacebutthewhole

ofarasit actsasahydrofoil

ils,wouldcause.Itisonly

becauseonothercourses,


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strengthens,however,wave

eresistancetoforwardmotion

eralmotion.Thistendsto

point,bekeptat its

heangleofleewaywhich

ofleewayreachesthevalue

nceispossiblebythismethod

duetotheobliqueangle

atwillslowdown.The

reasonablyuprightdueto

agewhentheboatistravelling

ldbeabout30,whichisthe

leshapeforgoingthrough

ainedwhenincreasein

tanceratioatthesame

asedmaximumspeed

eralresistanceofthehull

asingthes,7ororat'o

eedsinwindsof10to

equentsomostboatsare

sasgreataspossible.There

theirdesignsagreatdeal

excessoflateralresistance

havingamarkedeffecton

inedbyadecreasein

adsailswhichincreasethe

cebyarelativelygreater

micinefficiencycaneasily

estpossiblevalueofthe

ojibat all.

delsandtheforceson

l)andtheg^^'^ratio

rthesamecourseandsetting

makeleewayatagreater

symmetricalsections

eratioofthicknessto


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ththegreatestpossiblesail

nlytwotypesofcraft

hefirstistheslidingseat

00yearsinIndia.Thesecanoes

eendofaplankstretched

pright.ItcannotIthink,

usethemsailthemveryfar

gleordoubleoutrigger

dtothefarislandsofthe


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sonthehydrofoil.Ifnow,

illseparateandthehydrofoil

backwardsorforwardsby

ringswillcomecloserto-

angleofincidenceandthus

oingforwardsorbackwards.

themechanismitselfandthe

embreak,however,thehull,

bletogetbacktoport

ighspeedsailingvessels

temptto"jamherupagainst

Thisaccusationismade

ngnarrowhullwithafinand

fthisobservationistwo-

eisalargedifferencein

ofthesecraft.Secondly,it

bestforcedeadtowindward

otherwords,asthespeed

reateranglefromthewind.

erthanforordinaryboats,

believeaniceyachtsailsclose


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feetand26%extradrivefor

ovethewater.Theheeling

gemustbeweighedcarefully.

n,bothsailswouldhavethe

elythat,aerodynamically,the

aspectratio.Whenthe

ailareaof40squarefeet,the

alobjectiontotherig,butit

.Eveninastrongbreeze,

asytospillthewindinthe

ewhichtheapparent

ts.Forexample,withtwo


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entheluffandthefoot.

anandtheaveragechordor

orwingsare,asarule,simple

figure,theaeroplaneaero-

angularaerofoils,takefor

matelyrectangular

ingtwicetheaspectratio

aspectratio3:1,therefore,

1thenneedstobeincreased

dtobefullyaccurate,itfurther

ofthewind.Ifthewind

ever,thislastadjustmentcan

oryachtsails,areforrect-

meantheratioofheightto

heimprovingeffectofthe

radientofthewindistaken

ce(w=40)

workedoutforeight

mthesecurveshavebeen

ecoefficientofthrustat

illbeseenfromthisgraph

eyondwhich,norealincrease

ioimproveslightweather

gwinds.Fig.24givesa

hisdoesnotaltersomuch


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rse


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heraspectratios.All

ofarch1in13.5.Heeling

winds.Thecalculationor

efore,derivedfromthecoeffi-

ofzero.Thederivationof

Cgp.

erunitheeling

withabookoflogarithm

osoftherectanglesweare


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costofsailsisaconsider-

ignedwithaconsiderable

working.Thisattitudeis

aintoaccount.Boththese

eaterthantheymightotherwise

ndseveralyachtsbuilt

tiosof4.5:1 aerodynamic

cyofthetriangularplanform

isaerodynamicallyequivalent

etobesureintheabsenceof

atvalueandinterestif

evariableonconditionthat

waythattheheelingmoment

nswertothisproblem.

proximate.Imponder-

helowaspectratiosandthe

setheconclusionsderived

htheconclusionsofpractical


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anditisnotuntilthewind

ey,sothatbothsweepforward

texceptwiththewindvery

atrightanglestothewind

icallysweptforward

eofheelofthesamevalue

esaerodynamicallyatright

depressesthebowandraises

venafewdegreesofsweep-

gatrightanglestothewind

boatisbeingheeledtolee-

mtheboatbythebow.This

flow.Thismanoevrealso

ps.

sbecauseitistheoreti-

seaswellasforreasonsof

fthisweretobetried

hesailwouldbedistorted

dbeinverygreatdanger

econcavityoftheluffto

as possible.

sactinghorizontally,

ngtodrivetheboatverti-

rticalcomponentis,how-

wardfromthekeelorcentre-

ueangleatwhichthewind

rmulation.Itisapproxi-

heboatheels,the

ythesailsdonotalways

eristhat,inanincreasing

ughtooffsettheapparent


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mutualeffectoftwoaero-

m,onebehindtheother,

nglesofinclinationtotheair-

ectangular).Thegreatest

efromthewindwereachieved

pofonefifteenthofthechord

toeachotheratanangleof

dbestinyachtswherea

emostthrustforagivenarea

mtheforeandaftlineofthe

cesslateralresistance

thrust,whenused,though

atofanon-overlappingjib

overlappingjibanditis

ailarea.Whenthewindis

meforwardandisthenable

verlappingjib,hasamore

jib.Insomecases,itis


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micforcewillheparallelwith

nseenthatthecentreof

aygetsless,butthisisnot

fthelineofactionofthe

dmoreweatherhelmisneeded.

b,31cand3Id.Wehave

sitiononthesailbutthisis

ofinclinationwithsoft

mtheleadingedgeofthesail

ardsthegeometriccentreof

.Thismovementtowards


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fficiencyofsailsdepends

ruts.

improvement.

ent,themeasurementofthe

vertical.Evenwereittaken

slopedwithoutpenalty,the

dhencewoulddecreasestability.

alueof6 :1increasesthe

gthevelocitygradientofthe

sabout0.5theaspectratio

of6:1 isbest.Withthe

theforwardaerodynamic

ofthejib,lesseningboth.

efromrightangles

ordsofthesail.These

eadingedgewhenclose

thegreatestaspectratio,

pforward,thelesserfigure

ssweepforward

theangleofheelbecomes

ssweepbackwhichincreases

jibisalessefficientsailto

weresuchthatthesail

efficiencywouldimprove.

ebetween1in13.5

ically,especiallywitha

ribedgiving20%to26%


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versiononwirestaysunder

noewith2foot6 inchesbeam.

ruts.Thisisalways

rigandshouldbereduced

landdippinglugsail.

theirvaluetotheir

bcouldbeputintothe

eslooparelessefficient

rdabilityinrelation

hejibonthemainsailwhich

efind,firstly,thatthejibmay

ngitsvalueasasailonitsown.

closehauled,thoughitmaynot

hecentreofeffortislowand

bandsettingasmallerone.

usefulinnovationofrecent

presentavailabletoesti-

gsails.

:

ersarefaster

eatverylargeanglesofin-


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ncomfortablywithafollow-

ytheycouldpossessandmore

bsolutelyincapable

psutintheexpeditionto

of1 :2,beingtwiceas

wouldbecomealugsailas

andwouldbecapableof

gotowindwardare:

aught.


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achtimetheboatisput

rdippingthelugsailof

nthewindwardsideofthe

vebeenhardwork,because,

thewrongsideofthemast

eofthe mastsothattheheavy

ontacking.Anadvantage

agetowindwardinhandiness


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themidlineoftheboatand

gsailwhenthesailisto

ferenceaffectstheairflow

eworldorwhereMahom-

.Asimpleversionisshown

allyatriangleinshape

mically,itisveryclean

lluptowindwardduetothe

blyslopedbackwards.The

esperformance.

ndswillnotputabout

.Thewindcaneasily

oneofthevirtuesoftherig.

eheelingmomentissmaller.

robablyasgoodasailashas

nlybeimprovedbystream-


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ward,theplanformshown

efore,thegaffcouldbe

manceimproved.Thespeed

time.Atopsail,preferably

oughnotall.Thesailshown

whentheboatisupright

stheboatheeled,theBermudian

bovethegaff,thehalliards

ltinpractice.

micaxes.Inallcases,


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nterferenceononetack

onsidered,eventhough

ectratiowithastraight

ystraightthoughslightly

ailinguprightanddisappears

.Therearebutthreecauses

8%losscausedbythemast

tinthesailwhenclosehauled

sed,andthelosscausedby

gaininefficiencycaused

mpossible,atpresent,to

houldbeatrightangles

.Theirwindward

eparasiticeffectsoftheextra

reewind,theyareallfaster


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shoistedinagrooveinthe

obemadefromoneofthe

ossofefficiencyatpresent

couldbeloweredondeck

emainedaloft,however,

entionalBermudianmast.

ssiblethatitcouldactlike

okmightprove


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lessheelingmoment.Its

ectangularfellow.

showninFig.45might

thecatriggedboat,the


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emastwouldupsettheair-

omakethethrustforce

withtheaerodynamiceffect

ncreasethethrustforce,

ethesectionalterableso

ThesnowshoeaffairinFig.

ese,coveredbycanvas

ig.50. Ineachformer,


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thetrailingedge,thediagonal

tpart.Thesheetwould

awing,thewindwardside

tandthesectionwouldassume

ast,whichisshownincross

dbereefedorstowed.Itis

thisrigasuccess.

beofinteresttousfor

hor'sconceptionoftherig

sversionoftheaerofoilof

termediateslot.Boththe

of thesyntheticwoodsub-

gedges.Thisrig,ifsuccessful,

rethewind,withtheleading

cforcewhichisnotdriving

whichwilldecreasedisplace-

entoftheaerodynamic

nof4.Thiscomparesvery

chhasacoefficientofabout


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ctsdownwind,thoughsome

notfollowupthisline

etakenaboattowindward.

nbeforethecomingofthe

toanotherwithwhichthefirst

beingagestureofpeace,

od.Unfortunatelyforthem,

eywereambushedand,I

ethertheSamoansachieved

windwardthanIdid.

dthetail.ThisrigI

beattowindward.Inalop,

Therigis showninFig.52.

ble.Therigiscertainly


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maybewonbytactics,

ndofanotherboatby

yplacinghimwhere

nyourweatherquarter.

indofgreaterstrength.

atyourboatsimplyandsolely

s"ofanykindotherthan

ultinaworseningofone's

oatisfasterthanothers,

ichmerelyslowyoudown.

asyoucan,sailyourrace

oeuvres(alwaysbearingin

tchanceofwinning.

oussettingsandtrim-

gaswellaspossible.If

requickly,fortheboatwhich

hanwedo,notonlyby

eBermudianrigispossible,

toflateralresistancetouse

nwritteninthisbook,

sewillbegatheredtogether

paratelyexaminedandthe

explanationwhereknown.

rfaceonthebottomof

straightmast.This


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emastsideways

causeitisexcessive

letelypulledup

helmwhenitis

ingorGenoajib

resistance.Invery

sethes^^*r'ce

anvas,however,

atataspeedgreater

tautandtheleech

nthesamewayasina

ewind,theywillbe

,theg'^ratio

ingthesmallest

hell"""1* resistance

amicaxisbecomesat

ttobekeptup-

beallowedtoheelmore

issuchthattheresis-

uldbeallowedtoheel

ucture,theshroudscoming

gend.TheTwouldthen

nFig.54.Thisarrangement

smostadvantageousangle

ttherewasneveracomponent

wardsintothewaterfor,no

ertical.


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dedonaclosereach

ldbeneededwith

hatthemaximumco-

oursailwilldevelopis1.

cientoftheaerodynamic

ctedaroundthesailfor

enrunning,itisnecessaryto

ctionofthewindasmuchas

hesea,ithelpstodirectthe

lloonspinnakerisbased.

striketheMainsail

orwardalongthesailon

erwillspillmostofthewind

wnwardsontotheseato

ddiesformbecausethesail

ff,itwillbedrawnonthewhole

running,theairinthelee

eleeislessthanthepositive

wcanbeneglectedandthe

ofairstrikingthesailsfrom

ed,butthebagmustbeemptied

t.

atiois1,thereisno

nd.Evenwhenthespeed

courseandhenceitspressure

whiletotravelazig-zag

ookforwind.

boatistravellingnearits

raightlinetoitsdestination.

ybeobtained.

sinaspeedratioof

basedonthatratio.Slower

0-w).Thefollowing


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ndarounditthatother

ced.

hestreamlinesareaffected

ehauled.Thesewouldbe

ailsbutthedeviationsareof

great.Wherethestream-

ndwheretheyarefarapart,

imately,anellipseplaced

ataslightangle.Thesize

eboat,beingrelativelysmaller

reasethespeedofthe

boatalsocarriesanellipse

youandbeslightlyslower.

malong.Thismightbea

whereyachtsareracing

uhavelittlechanceofclosing

osition."Themaximum

onyourleebowandyouare

sufficientlyclosetohim,

outor,byasuddendiveunder

oarea2ofhisboat.The

induceathirdboattosail

hirdboatshouldbepositioned

chanceofbreakingthrough

k,tocrossaboatonthe

lheadyouasyouapproach

isstern,ontheotherhand,


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ewhileyouradvancewind

tsheadshimslightly,

er.Youarethushelping

uareinhisarea5 where

ightlyunfavourabletoyou.

othewindaspossible(where

engthenthedistancebetween

nterference.

rableposition.Thewind

slightlyfaster.Hehastwo

chcase,duetoitsincreased

headvancewindfromhis

shouldnotsucceed.Or,he

fromyoursails,atthesame

ifyoutackalmostimmedi-

ge.Repeatedtackingtocover

efore,aboatinarea3to

ottack)lethimgoandtrust

ouwilldosotoowhen

hyourleeintoarea2.

bletosqueezeupto

hissothat,asyouhave

feleewardpositionineither

ndthegreatestchanceof

artofyourellipse.

favourablepartofhisellipse.

eaheadtillheisarea5.

ilaslightlyfreercoursefor


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boatisapproximately

on.Thesizeoftheellipse

randthewakeofeddiespassing

tiallyofthesameshape.

cultwithabeamwind

morebystrengtheningand

soincreaseinspeedismore

kingaboattowindward

ofcourse,heis atlibertyto

essfrequentlythanonother

ctedbothupwindand

e,wheretheyarecrowded

separated,thewindspeedis

upoftwopartialellipses,

yingairaroundtheboat,

ctionofthesails.Ineach

aboatonthesamecourse.

fasterandturnsawayfrom

lowerandturnstowards

atanovertakingboatmay

nakercollapse.Ifthisfact

othezoneofeddiesandbe

nlyaslightreductionofspeed

Thatis,thesmooth

ctionsdownwindofthesails.

eathersideofthesails

hoftheseplacesmaybe

enexamining,thiszoneis

ofeddiesareexamined

ngtowindwardonthelee-

boatandvariouspeople

snotbeenshown,however,

utsuchahole.Ontheother


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andaknowledgeofthe

uchvaluetothesailing

smoothestofbottoms

acleencrustedtubwitha

fromoneplaceto

igs.58and59aretwomaps

emisphereoftheworld.

eofthesamevalue.For

willsupportacolumnof


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savailable.Theresult

surveymapwithmountains

cchartisusuallydrawn

temperatelatitudesinthe

about10to15milesperhour,

susuallypossibletopredict

entyfourhours.

ghtoplaceswherethe

sthewindtodeviateto

tinthesouthernhemisphere)

pressureonthesynoptic

ationisthatasouthwind

thesurfaceoftheearthbut

wardstherisingsun,dueto

fnorthlatitude,wherethe

ndthatthegroundbelowit

erhour.Themomentum

thenpulltheaireastwards,

60 ofnorthlatitudeto

ofonly500milesperhour

ds.Thiswouldthencause

face.Thus,theairdeviates

cecausedbythetendency

hegradientofpressureshown

softheisobars.

BuysBallot'slaw:

rpressureisonhis

rnhemisphere."

lblowalongthelines

aroundtheroughcircleof

wsearoundtheroughcircle

owslightlyacrosstheiso-

ngoutlikeaninverted

Fronts"whereonekind

storeachanobserver

uddenlyreplacedbywarm

asuddenveeringofthe

Cirrus,Cirrostratus,

efrontispassing.In

bsoftheY,thepressureand


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dkeepingittherefordays

ralisestheeffectofthe

isobars,becausethereduced

otationinthenorthernhemi-

ardsthelowerpressure

sobarsoffrom10 to30

vertheopenseaandgreatest

arthesurfaceofwater.

themeanvelocitiesatother

suredinonewindgradient

hericconditions,beinggreatest

thoseaboveandleastwhen

lenceoreddieswhich

eeddieswhichcausesthefall

seithertoincreaseorde-

boveorbelowitsaverage

otationalmovementand

sspeed.Manysucheddies

dsbuttheyareveryvariable

ntheywillcomeinanygiven

pencountryandoverland

mwoodedcountry.

ezes.Itconsistsofa


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dedshorehasthecharacteri-

nts,pilinguptheairabove

65and66.

han42 doesnotgreatly

n42 areturneddyofair

windisstrongerthanthis,

notsousefulfordrivinga

steepnessorotherwise

winds,exceptsofaraswith

etimetheseashoreisreached.

dingtoaboutfourtimesthe

oisreplacedbyturbulent

illaffectthewindflow


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yeroftheatmosphereby

entwherethesurfaceheating

mportance.Arrangedin

ows:

heatabsorbedinevaporating

ofthermals,probably


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suchawindasshownin

atesthenormalseabreeze,

a.Italsotendstobegusty.

overedwithseparated

owitwithcompensating

ownwardaircurrentaffects

s,atthemoment,rather

entsonthewind.As

madownwardcurrentand

donthenormalwindflow.

aretobefound,notdownwind

tatthesidesofeach.This

ertogetthebestvaluefromsuch

chcurrentoneisinwith

esenceofcloudineither


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windisstrikingotherboats,

therewillbeaperiodic

eriodslastingforafew

ndthewindspeed.

urbancesintheatmos-

orizontalextent.Over

ffectsofmanysmallthermals

toftheatmosphere.This

blethermalsascendingand

overthelanduptosuch

urfaceofwhichthemost

ghts,thebreezesets

betweentheshoreandamile

suddenwithasqualland

ears,themoresuddenlyit

ISmilesoneithersideof

height.Insomeplacesin

helandtotheleftinthenor-

andfailssoonaftersunset

hduringthenight.

thelandwhichbecomes

essureoverthelandascompared

irtoflowtowardtheland.


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eairincontactwiththe

estorushoutofthevalleys

windonthenorthernshores

rhour.

ayerofair,thewind

orewindofstableair.The

lingit.Fig.81showsan

ndbeingdivertedfrom


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Documents

Sailing Aerodynamics