Human-powered watercraft

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In striving for ever higher speeds the flimiliar racing shells propelled

by eight oarsrn en may have to give wa

to LW con yen rional wa cercra ft.

Such a record-setting vehicle was designed and built by the a ud2ors

by Alec N. Brooks, Allan V. Abbott and David Gordon Wilson

C .w

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nih recently the slender shells.

or racing rowboats, made

fa-miliar by the Olympic Games, the races on the Thames River in En-gland and other rowing regattas held throughout the world, were the fastest human-powered watercraft. The

fast-est of these, powered by a crew of eight

oarsmen, achieve speeds of 12 knots

over a standard 2,000-meter course.

(One knot is equal to about half a me-ter per second.) Human-powered

we-tercraft that are not bound by the

ar-bitrarv restrictions of officially

sanc-tioned rowing events are likely to equal or surpass this level of

perfor-mance. Designers of these

unconven-tional craft are disrensing \vith oars

and taking full ad';arttnge of modern

high-efficiency propellers. They are

even dispensing with hulls as the

ex-plore innovative ways to reduce the

re-sistance ainst motion, called drag.

that water exerts on a moving boat.

fndd. two of

us (Brooks and

,-'bbott) have developed just such a

record-setting human-po'.vered water-craft. The water-craft. iii,i' Fish I!. is

rid-den like a bicycle. I: has a pair otT hy-clrofoils, or ander'.vater wingz. and a high-efficiency propeller. It enables a singie rider to complete a 2,000-meter course siniflcancly faster than a single

rower in a shell can, and it has attained

a maximum speed of 13 knot.s over

short distances.

ceardiess rjf desienwhether it is

-: crude rlotation deicc ropeiled

b underwater kicking, a wood raft

pushed alont h' poles, a dultout

Ca-noc PC'.arCu b. padalcs or

tao. ed forv. at! s':.ecaing 'earsev-cr. '.vatrcrn(t rut:st eotitcad '.'i'.:t four

baie

OrCCs: .veight. lIft. thrust and '.rag. Wih: and lift are the simplest

cetounacrs:ai'id. \Ve ight is ia1pll.

the gra.ita:ionnl force nulling down on the craft apd its occul.'ant.: Ilit :s

thc force tha: ac:. up.:ard.

oi:ntcract-the v. eight. ;' long ::.

i hut does

TECHNISCHE UNIVERSITEFT

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TS'- r-1

Laboratoriurn voor

Scheepshyrcmechanjca 1 L.

Watercraft

not experience any yertical

accelera-tion, lift is equal to weight.

For most watercraft lift is generated by buoyancy: the displacement of wa-ter by the craft's hull. The lift is equal

to the weight of the water displaced,

and it operates even in the absence of

motion. In addton many high-speed

boats take advantage of dynamic lift. which is produced as the boat moves through water. A common example of dynamic lift is planing: when the bot-tom of the hull continuously deflects

water down'.vard so that lift is pro-duced as a reaction force .:\boat that relies on planing for most of its lift

rides higher in the wateroften right at the surfaceand requires less buoyan-cy. Until recently designers of human-powered vatercraIt had not been able

to SUCCC5Siifli incorporate dnamcc

hit mato their vehmcles.

Thrust is the force (produced by the

actions of the operator in the case of

human-powered watercriaf:) that pro-pels the craft. Drag is the force that by definition acts in the direction oppo-site to the direction of the craft's

mo-tion. If a coat is moving at a steady

speed, the thrust is equal to the drag. Itt

summary. at constant speed lift

bai-ances weigh: and thrust balbai-ances drag.

In order to translate efficiently a given human po'er input into speed

the most imçcrtant objective is to

rain-imize drag. One oh'. ions way to lessen

drag is to reduce the '.vciht of the

boat. Once a boat begins to move. :ms

source of liii airnot

al'.' ass exact.;

a drag reit:zy. By rn:nimiztns

',vetont 01 the Doat the requirea lttt t rcducd. and hnce the draz

as.;oc.:t-ed '..'ith the lift is lessenas.;oc.:t-ed. Since :ae

craft's operators are no:

likely to

be overweight (assuming they are

healthy, athletic individuals to begin

with), the weight reduction must apply primarily to the vehicle itself.

Efforts to this end have led to racing

shells that weigh only a small fraction

of the opera:ors weighta relation

similar to that of a modern racing

bi-cycle and its rider. In the past shells

\vere generally made of cedar, spruce and mahogany, and they were made

lighter by thinnirtg their hulls. (Indeed,

the term "shell" arose because a

care-less finger could easily puncture a

wood hull.) In the 1950's experimental

shells that had a skirt oi glass-flber-reinforced plastic were tried, and by

the end of the 1960's commercial!.

available composite-based boats had

challenged :he dominant positton of

wood boats in rowing cu'cles. Toda'.

the wood sacil is becoming a

rar-itv. Soohisticated comoosite materials

Lorsistineo re

\i"

with tioers Ci C polymer ororai;ide have brouehtetown ate ue:gnt ot toe

ligiatest s;nge-person sheil to less titan LU Kilograms.

ssiiming that the weight of the rue-1. ing she! nas been reduccd to practical minin'J.:m, a dsignars lion must turn to other wnys of imizing drag. Shells ha'. e '.vhat ac called disriaceraer,s hulls: vir:aailv a: their lift is rrod uced by trie huovanc

of the huh. Displacement hulls h.:'

Inc uraque P:operz that ther dra at' proaciles :e:o Cs tacit spec:l tiiOuf the water urraches zero. }-lcn:e a

'-ctV lOW s::ees displa:cracn:-:... 'r,iaies have ex:ren:ety Is L.,aa

.-\'IONG THE FASTEST munn-povrid -atercra(t are o':rmtic':al ni:i:,

the authors' uiico:, e':cion:,I ve:ici. 't,: [ih ii. The shcii. si'wn her

tiu ret

:our-rirne ()lv;npii Jnh:i ":tn 131',;n. ve 'uil by .\tIrd St.irnprli .'.G u So

l-ivin FTiJz ii. ri.idu: by 'ie t:heauth' i..'hb,tti. h .)s,irCd bap'i.t!-c'.:ii'n p

pdller -jnd i:pi'orred S two h drotoi s. r iihrwtcr ,s. c b1,: tcizI;.

iits .i:

,'-c-::1-%

,.. :'

are among the most elficierit of all ve-hicles. Racing shells, however, do not

operate at low speeds.

As a shell's speed increases, its drag

increases dramatically owing in part to

the formation of waves that emanate

from the bow and stern. The energy

needed to produce these waves is

man-ifested as wave drag. Wave drag

in-creases rapidly with increasing speed but in an uneven fashion because the bow wave can interact constructively with the stern wave (so that the waves are in phase and reinforce one anoth-er) or destructively (so that the waves

are out of phase and tend to cancel one another) as the craft picks up speed. At

a speed called hull speed the bow is at the crest and the stern is at the trough

of a single wave; in its passage through

the water the hull has literally created a hill of water through which the boat

must push. At this point a great

expen-diture of power is needed to increase

the boat's speed. The human power plant cannot supply the required ef-

-fort, and so hull speed acts as the

effec-tive speed limit of a human-powered

displacement-hull vehicle.

Hull speed is proportional to the

square root of the waterline length of

a OETJ human-powered watercrart

trve lông displacement hulls are

therefore less hindered by wave drag than boats that have short hulls with

the same overall buoyancy. On the

other hand, for a given buoyancy long, slender hulls have more wetted surface

area than short, wide hulls. The

great-THLST

er the vetted surface area, the greater the drag caused by the friction of the

water as it flows past the surface of the

hull. This type of drag is known as

skin-friction drag. Hence as a boat is made more slender, wave drag

dimin-ishes but skin-friction drag then

be-comes more of a problem.

A hull designed for speedy boats

must therefore be shaped to minimize

the sum of wave and skin-friction

drag. Shells are designed to compete in six-to-seven-minute races at power levels of about half a horsepower per

rower. (One horsepower is equal to

ap-proximately 750 watts.) The resulting optimal length-to-width ratios of these sleek crait exceed 30. A single-oersoa shell, for example, has a length of

be-tween eight and nine meters and a

width of no more than U centimeters.

Iout that the optimal shell

shape results in a skewed distribution of drag at racing speeds: 80 percent of the drag operating on the shell is due

to skin friction and 20 percent is due to wave production.

Given

_{nant source of drag operating on}that skin friction is the

domi-a shell domi-at rdomi-acing speed, domi-a substdomi-antidomi-al reduction in drag is possible if skin

friction can be reduced. Skin friction

arises from a thin layer of water,

known as the boundary layer, that

flows past the boats hull. There are two fundamental types of boundary layer: laminar, in whiu-h the flow is

smooth and steady. and turbulent, in

LIFT

!/

a LHT

(j

DRAG

FOUR BASIC FORCES must tre c isdared in designing boats such as the racing shell shown her's: wei2ht, lilt, thrust and drag. \Vaiu!rt is the gravitational force acting on the bo:it and rho operator. Lift is ziormurllv generated by buoyancy. tit's upward force eguai to

drew cigar o the water displaced by t:,e hout' hell. Additional lift, called dynamic lilt,

car: be productd by the flow of water urrdtr the hell. Thrust. in th case of human-powcr'sd water vehicles, is the force produced by the actions of the operator (hero sen rowinu) that propels 'she craft forward. Drag is the resistance to the boat's forrvard

mo-tier: it aric.s in n:os r craft frrri the arcuiton of a wake (wave dm2) and the friction tot seen the hshi and the water tlowirrg past it (skin-friction drag). \\ hen a hoar : as a

constant pe'sd. lift balances weight and drrusr balances drug. TIre key objective in boat d'sin i to minimize drag at the normal operating speed of the boar. At th's speeds reces'

sarv tOt corr.peririve rowing. dr::g a minimized by making a shell light. lung an'l narrow.

110

''

which the flow is chaotic and

un-steady. Laminar boundary layers pro-duce much less skin-friction drag than

turbulent boundary layers do. The

boundary layer on a shell is laminar at

the bow, but only a short distance back

from the bow it typically undergoes a

transition to turbulent flow. Drag is

significantly reduced if the transition is delayed, thereby increasing the area

of laminar flow on the hull.

One method of extending the lami-nar boundary layer that is applied in some specialized underwater vehicles

is the injection of long-chain polymers (sometimes referred to as slippery

Wa-ter) into the boundary layer near the

front of the craft. Race-sanctioning

or-ganizations are not likely to allow this practice in competition, if for no other reason than that it pollutes the water. A similar anproach that might be al-lowed, however, would entail

careful-ly cultivating a 1a'er of naturalcareful-ly slimy

algae or some other innocuous

micro-organisms on the hull.

Boundary-Jayer suction is another technique that has been applied to

sta-bilize a laminar boundary layer. In this approach fluid in the boundary layer is

continuously "suckea' into the boat through pores or small slots in the

hull surface. Shells could make use of

boundary-layer suction if the' \vere

outfitted with a porous hull that would allow water to seep in slowly. A small

pump would serve to bail the water

out occasionally.

The texture of the vveteed hull

sur-face can also pla a role in the

re-duction of skin-friction drag.

In'.es-tinations under the ausoices oTThe

ro na ics and S p ace

ministration have sno\vn that a slick waxed surface does not always result in minimal skmn-rrtction drag.

Sur-races with very tine grooves running

in the flow direction, called riblets,

have shown 6 percentlOSS crag than

sn surfaces.

iblets have been tested on rowed shells by a group from the Flight

Re-search Institute headed by Douglas

McLean of the Boeing Company. The

eroup covered a single-person shell with an experimental plastic skin in

which grooves been formed. The

spacing butween the grooves was

three-thousandths of an inch (about 80

microntetersr.er than the groose

sPacing on phonograph records. Tests

inhcateti rhnt the shell's maximum

speed was incrcisea b 2 percent.

A!-though this ma. eeni like an irsignifi-cunt amount, it a.:uis :tlent to a

four-boat-lengta ndvnr.tage over a tnndur

2,',)ii).jniu' rae-c.

Ott the emisi's cf such encouraing

suIts thu cxr:e:n',catal skin

up-pried to the -u;i o: the U.S. Olympic

- ..- . '-.-<- -. 4 r.,

.5

-0

0 5 tO 15 20

SPEED (:<NOTS)

\EE LEVEL neccsary for a I mtan-powcred watcrcrrft to

a ertCin sceed for certain enuth of tie depends on tho 5 dcsian. The rph at the left shows the po\vcr reavirod for a

n _{helt. which relies ott the displacement of watar It its hull}

met of its lift. compared with two other rttft designs (one the .tiirhorsl, which, rely on the t. vnanic tilt pruduced by ofoits. At tow speeds displacement-hull craft are more ei5-thin hydrofoil crift. Actually hydrofoil craft hat a a

mini-speed below which the ivdrofoils cannot support the cant-d uetcht of the craft ancant-d the operator. At higher speecant-ds.

how-a men's co>:how-ad-fout- rowing sh.eil. oxed beat is steered by a eoxsv cia.

does act roy. but cads out the

ing cadence.) The team made an ;ilcnt showing. \vtrinine the silver

al in :he 1984 summer games.

addhion to low drac, another es-ntiai inoredient for a successful tg shell is cood proculsivc

effl-cy: as much as possible of the

pow-oin riL:rnans must be converted useful thrust. In the case of

row-two major advances in propulsive

encv date from the niid-l9th

cen-One was the development of the

em riger in 1843. The rigger is a

duke device attached to the side

e boat. The oarlock, or pivot point e oar, is located at the apex of the

d. Since the oarlocks no longer d to be attached directly to the

'ales, or edges of the sides of the the hull could be narrower (re-ig wave drao) and the oars could )nger (enabling mowers to take

rand more efficient strokes).

e second advance was made in

the sliding scat. Until that time

i boats were propelled through se of the muscles of the arm,

ders and back, whereas the larger

Ics of the lees were used only to or support the body. The motion

rc'.ving was one of heavy strata-:ainst a slowly moving rcsisiar.cc.

dich-.z-seat trranuerncnt allv. S

crc'. of he cc in uscies to be bar-L'N: ;SH

:Fr D:S:N

EECN PC;NT FC. FLYLI:O FS:-1

2

tossed as the seat moves fore ar.d aft

s tlt the bending and stt-aichtcnd-,g of

the legs durine the ro Inc C\ dc. The

tirst sliding seat .vas a rather crude

de-vice consisting cf a sheepskin pa5

slid-ing on a greased panel. The slid:n seat on bearings. still in use rodac, was

in-vented in the U.S. in 1857.

A shell svith a variation of the slid-ing seat was rowed by Peter Michael Koihe to win the 1981 world champi-onships in Munich. In contrast to con-ventional shells, which :qave sliding seats and fixed riggers and stretchers,

or footboards, Kolbe's custom shell

was equipped with a fixed seat and a

sliding frame that supported the

rig-gers and stretchers. Under this

ar-rangement the rowing motion is the same as the motion for conventional shells, but since most of the rower'.s

mass is on the fixed (rather than slid-ing) scat, the oscillations of the center of mass (which more or less coincides

with the rower) are greatly diminished.

This in turn diminishes the oscillations

in velocity that a shell is subject to as it travels through the water. (These oscil-lations are manifested in a

convention-al shell by its distinctive jerky motion

when it is rowed force ful lv.)

Because skin-friction drag is not a

linear function of the velocity of e water in relation to the hull itt s ta fact ropomona1 tO the suuare ot toe va-a mictuva-ating 'peed va-alwva-a\ S pro-duces more drag than '.voujd occur if

the boat rncD\ ed stcadff(' at the average

.1 .2 .5 1 2 5 :0

DU.ATlCN C .CTIVms' MINUTE5)

ever. hydrofoil vessels are more efticient than displacement.h::lt

craft. the graph at the rih t stt'tts tto,v the power a champion

athlete can seppiv diminisltes with the effort's duration. Fcc brief

dui-ariis rh -auwc'c output gettareteci by the cyctin mrts

considerably higher than the our:ct zeneratsd by the row!:i

mo-tion. tn aptnul tivdrsfil design could inke it possible to roach

specus of nero than 20 kitots. Such a feat would require :.:xor

levels th et can be aettieced only by cycling an only for a icw

seconds .A orft incorporating 'ech a hydrofoil would he diEecit

to get started: its 'takoetf' speed voiitd be more than It :nuts.

speed. The drag reduction obta:r.ed by

Inc _{ttn2-rieeer arrancement :s} slight. hut :1 is enough to make a

signif-icant dierence in the racing

In the 1582 world championsh::s fl-c

boats in the men's finals had fi:ed

seats and sliding riggers. In 1985 ad six

finalists used sliding-rigger boa....

ter 1983. however, sliding-rigger boats were ruled ineligible for competition.

lthough the addition of the rig:er

I X. and the sliding seat signiflcantiv augmented the propulsive efficiency

of rowing, rowing nonetheless has a

fundamental limitation. Oars and rad-dIes are basically drag devices: they generate thrust by slipping backward through the water. The slippage repseats an efficiency loss; it can he re-duced by increasing the size of the oar blade, but only to a limited deorce be-cause of practical constraints.

More-over, the aerodynamic drag caused

by We blades when they are out of the

water during the return stroke can

be quite significant, particularly

tin-der windy conditions.

The eficiency of a propulsion evs_

tern is dCfined as the ratto of useful

power output, which is the product of the average thrust and the velocity, to the human power input. The derailed

physics of rowing is not entirely

under-stood hut analysis by many invega-tots has rut the propulsive etbc:encv of ro'' inc at between 65 and

:. _;c-? - -r \\çy. LI cc.\ .trc.i to s

rcw'cr

:..

.t

..c;\: .h rt

'O '(''fl

J t4..,. fl 'C nd air. . 10 I!:Ci

.K.:r:ci :'cl:

:c dv'.

tee. 'iLl'. as iCIS. : lever Cf

ln:vrLlly.

cre the

."f fl1iifl easulti-tele.:

i.:il fO_

CIS :It tic turn n the cettur:..

ur.t--ocred prop

r-nrt'.'en Los\.ctc

a tact being evelopc.i for reetcal

ransport:tOn p.::roses. Such

propel-er-driven bo is aroved :o a

15:cr and luss :frinz than canoes or

o: boats. In the 1 SOcs a three-rider

oelier-dr'.ca catar.t.raa

:a

t'.vn-tu1ed boat) " as sao :t to he 1

eat faster than 5 three-oarsmen shell

ver a 103-kilometer course on the

Pames River

Some LSCJ\IfltCSCS Or prorellers tre that the' can be fouled wth weeds

tad can strke bottom a shailcw cr hut otherwse roocflers are

par-h

'-'-p--ieje-dications {see -Th. Screw Propeller.

w E. Eugene Larrabee; SC:ENTIFtC

\\tERICAY. Juts. 1980]. Sr-hlad:X

i.

ieh-efieciev propeller desiens

an he applied. s:nce the po\ver level :s cite lo'v. _{In aeit:on. rroL'eilcr-tD}

aecds are low enough so that cavtC-ion is not a preblem. tCavita::on. th ormation of bubbles of v:ater vapor.

rises 'vhen the absolute pressure on ome part of the :otatmg propeller s

educed below the waters vaoor

pres-Ire: it

_{reduces etcieacv and can}

ause excessis e ::ear on :he blade

sur-Sces.) Several rte.v human-posvered

etercraft have been outfitted svith

ropellers whose efficiencies exceed

0 percent.

The rotating motion of proaellers

so makes it relatively easy to drive

tern by an arrangement of pedals,

rockets and chains much like that of

cycles. SUCh an arrangement takes

Ivantage of the rapid and strong

ovements of the legs. The circular :daling action in bicycling remains e most efficient practical method of Llnsferring continuous power from

human being to a machine. (It is tt coincidence that record-setting hu-an-powered air and land vehicles

de-ad on a bicvcleiike drive train.)

;\ champion cs clist can produce

cai

at Tiu.'.I

rn cli:.

:.ir 'LLdS

o

vet rots exertion lane for six

all. itO'.\ Cs er, the e:

: tpuf is :e.-sc:.tl

no tore than htdf

.her'c-Vrios l.

tON ..:eet

:adstcticn. fiCi tdno :Thnz rIte.

y;teigi-.t. redul-eran'\ 'enni'..n.i

s:cni ccnuttton end .ie:crn-in;to1

cf toe C\ vist. lhe traditivnai i-os _pa

:t:c't:Cn. in which the ro.s ci si:s stiil a::dbrings into play oni he in tisClcs

of his back. shoulders an: arms.

eonilcrablv less poss er :.'' the

cv-chat motion. The addition cf the

slid-Inc selt. ho; CS er _{ncreases the p055 er}

level of rowing to rival hat of

cv-chatat least for periods of more than a fe-v minutes. (The shcrt-period ad-viatage of cycling is lost .sf:er about a minute because of the limitations

in-osed by the human circulatory and

respiratory s StemS.)

The inherent advantace of

:eddal-ivea-propeller

_{boats ocr rowed}

bo,ns therefore lies che:is in the fact

that cars are a less efficient

meeha-nisn'. fr channeling human energy to

the propulsion of the Lear.

F;:rther-more. a rowed boats une'. en speed

cx-more of a drag peneh than the

smooth. coatintious seed that can be

achiei ci with a rroPe 11cr.

esisners of fast hum n-po.\ cred

ss atercraft has e also at:ernued to

mamjze drag in novel s Os. One '.vav to virtually eliminate wave drag and at

tne same time reduce

sktn-trtctton drag is to submerge the hull: the

orera-tor ,vould have to he supaorted above the water by narrow struts extending upward from the hull. The

minimal-drag hull in

this case is

teardrop-shaped, with a length between three

and four times its width.

Such a configuration is like that ofa

unicu dc. and balancing would

like-'vise he difficult, if not impossthle, for the rider. Theodore Schmidt alleviated this problem somewhat by attaching

four small outrigger h drofoils to an

experimental submerged-hull craft of

his own design. A tricvclelike

arrange-ment of three smaller

submerged-buoyancy hulls would be stabler but riot as efficient. Since the ratio of stir-face area to displacement gets smeller as disalacenient :ncreases. one rig hull

\1.NPO\VERED ',VfERCRA1"T dkpIa-csuortcd shapes. COilStrUclI(i, rivri:ils

i propuLsion de'iccs. Rcttively primitive craft .sre pnled 'zc) or paddted (d. and

mdc of sitch di' erue narcr1 materials _{as rcrds, 'ood and miittI kin. tnre rolern} it are madc of 'jod or metal and_{nrc rowed (. :iri.ltion that cults Pr Ic ;se f the}

is. sboildrr _{nd hccL-. or are paddled cit h fc.;t pc dais. britigimn. iito p Li the nr'ii'f}

muscles (v). Pcriul.drtveim- pro pet icr boats I 111%e ureater prop:Iim ti

:1;-ihan ritt;_r ro;' ho;mts or _{ajufe-.' tL'Ot huatS. '.m ci desi'is aid tulsa ts lava alco} back ott the such :rufr oumc'uumter. TIe wtared i:]! f fte..Cra tft;:tmjt

:Lti;:IL:Itul c-alt

j. for

_{;m'ancc-. c;fecttic:i jnnatL the pr&lmtt:n .t 'arc}

.,..

.!

:es ;;rcv frvt tha: three n:si1ier

hulk ..ith he ':rtc :e.t:l bar''. ares.

:'tl;s:ei:g prob. n

if a

ui:'..lcr' atCi ':11 could bc sob.ci H:

overarcr 'i the ':11--it a _sibrnerinv. u;t

srrerntr.cu '

1 bc enough :e encice

a ride disiriae.;s :a iuch more s. ,;tar tad

has more .urf.;v sea than ut hull thun provhlv iust anou::hs bus anc to Sn:;-port a aersons veigot. Altltoi:gh it is

not optimal for human-powered irans-pot t near the surface of the a titer. a

hnmen.ro.'. ered submarine could Icea

great improvement oser a skin diver

'a ith fipc:-s. In the earls 1950k a

tao-person

_{himan-os ered}

_submarine

called the lsltn-Sub. designed by Cal-vin Gci:gsver. 'a-as produced in limit-ed quantities b the .'\eroet-Genera1 Corporition. Pushed forward byta in

h0-nsil1imetei- counterrotatinc pro.

peilers. the sluni-Su'o reportcdlv could

achieve speeds of seven knotsabout

three ames the speed at which a di'.er

can ssvim under.vater.

Other designs seek to red uce the sec

ond m;jor dreg component, skin-fric-tion drag, by employing dynamic lift

to rause part of the boat out of the

sva-icr and thereby reduce the boatk

vet-ted surface area. Although dynamic lift does incur a drag penalty of its

own, in many instances the reduction in skin-friction drag more than

cons-nensetes for the drag generated as a

by-prod ict of the dvn antic lift.

Human-powered water vehicles that

take advantage of the dynamic lift achieved by alaning are still in the

imagination of designers, but

anoth-er way to genanoth-erate dynamic lift has

been arplied successfully: 1-ydrofoils. I-[ydrofoils are underwater '.vings that

produce lift in the same was' as

air-plane wings prod uce lift. The required

size of a hydrofoil '.ving is quite

mod-est compared with airplane wings.

For example, at a speed of nine knots

something under a tenth of a square

meter of foil area is needed to produce

enough lift to support a single rider

above the water.. hydrofoil designed

to produce the same lift at twice the

speed would require only a fourth as

much area.

,\lthouah the small wetted area of

hydrofoil .vincs results in minimal

skin-friction drao. Isydrofoils do incur a ut:rfereat type of drag...the h

dro-foil tra'.els tlsrouzh she '.vater it leaves

heltind a vortex wake, iust iS arplane 'sings ia The enersis expended in crating :he ' ortex wake iS manulcsteu

as a drag callc.l induced ulrag. .\lso. the spray kicl.si ;:p bvthe'.crtmcai

trls c.iml'l'C'rt:mS -ic hs ;lrofoil us '.he

cut tlsru:eit mite .ri,ce if jh sitet

suns in altl:caJ drag

-.\ruc'.l'er :ss::cr p.rol:iern 's ;th

ni-ri.' h. i.t-co: .:u It s

I to 1..aL rehn:\ hi.tli '

i-pce.h. a.forc tht\ .0 i 'ta.e c:f.''

:ersei ..s

It. roftis proeucc zcro ft at

o 'cccJ. .otcr

sOi

tu is

a dtspcc;rtaz ha!1.

i :-e.

I!C'.I :cr the jflittCl tout pilses

a tzt. A wit

!c.ted for a1-t

speed may ha'c:o he movtr.e

ouh

e valet at I U knots before tt

cneretc otigh lift :o support the ft and rider. This .soced a i\ cii he

ssih!e to achieve wh:c the craft is

1 snreortcd on the

v.

ater by its

nine meat hull .:roer hdrofoii

no could reduce the ;ekcotf speed. the drag caused by the increased face area would not chow the craft

co as fast.

Stecking hvdrofoils o that smaller

Is are placed beiO\V larger ones. as is

tie on motorized h' drcfc:l esseis.

ght C ire ant vent the ::oa lem.A emIt

:h such a tapered Izader'

arrange-at of hvdrofoils could take oif arrange-at

v _{speed on the large upper foils.}

ce sn:ctent st'ced has been

at-ned so that the lift produced by the

la:vem toil

enougi i:csip:.

c:.::. the era: cualLi c ip :ur:hc:.

the inrer !.:l

t ci :hc .

cbv red acme ,.2. Reeai. se cf

the irthot:ent i!hcidi:s IsSC'CitucL3

t\ droro:!s. haunt- on cr-ru h'.

:roctl emit -ro not hu'.c thL'5iC

cn:e.i irotenilul s ItI!mn-,o.s e:u

tnt-t:a:cs. '.vhich tta\it_{ucl.i. ed spceds of}

ate me tItan _knots.

Th:tl receaLly all h"an-pc.. ercd

':atcr-spred records vere held by

c:nacemcnt boats propelled h'; ours. \\ium the intent of exceedinc these s:s, two of zis (Brooks and Abbott)

I 'S4 desioned and built Fim:ng Fish

I. the first hydrofoil apabie of sus-tamed flight on human power alone. The tickv problem of initially cetting

the craft up to takeotT speed. which

had lagued earlier designers. '.'. as

by-passed initially by eliminating the need

for a displacement hull. Flying speed

was attained by catacuit:ng the craft

m::t'D the .vater from a floating ramp.

ay_ch as jets are launched front air-era:: carriers. lsing thts tiumag start"

L.nc tag method. C) clist Ste' e Heug.

'"C /j\1 /1 Ii

_{iillli-i)''j,I :1.'}

1 :ie'.t _I-i.:tcd .u;tJ

tI,L

;uJ lb. (.L:tt. cçd b% 1 :il-Iri.ul,ii.ir-:!11cic:.iV ; j.ii,.r. t:iCS ,ii

i.

:..t

..f eb,t tu..i.. Its d<r jest

tue't.'. tile itr'- t. u. .1 1 r erait el ii.

'u'e

iiC

- :;rl -.:1:;ir-i:':.1cl :1, :-

tr,,

tt IP 1') 'uk-I

j;i C.lz :ui:-e _{eolJ ntcU.lk:. cdalc-d}

I a clisinuec of 2.,.I,)-r.te_

tcr Ii rdx aiirtutcs '1 cecouds.

eclips-ic-: :hc .; c':-lri recr.l tot 1 si:tCe mcv Cr

by ii scconds. lhc tit.tts. ef

course.

are net dircrilv con:r.rtblc. becaie

ihc _{ro'. inc record}

_{.' as set front a}

Stait tag start.

Fish I has a high-c:heiacv. pcda-uriven propeller ndIno slender

wmt-.cs supcc'rtcd b'. _{narrow vertical} struts. The main '. tao, which carries

90 rcrccat of the craftsv _{eioht, has a}

tar _{\vmngspttn (1.8 meters) to}

mini-mizc mnducea crag and a smati chord,

or . :dth, to reduce sk:n-Irtctton drag.

Th smaller front wing hasa

configu-ration much like an inverted T and is tightly loaded: its main purpose is to provmde stability and control. To this end it is fizzed with a small, spatula-shaped device that automatically

con-trols the depth of the wino. The device skates ot em the water surface,

continu-ously adjustino a thtn flap (analogous to the elevator on an airplane tail) to

'.vhich it is !iakcd.

The front nine strut do uimies as a rudder and is connected to hicz dc

.it-'(liS _{'ri tt CuriLit .rriti ,u.Ur.rt :r.nt -.r}

lELt t uitrl t'.'" L'Ch _{ruke.fiee'I run a st:iTtlt_ ii:. .Ltti it}

's';iet tiletivdrt'jiS "tiv _{ts euirtic,tkd .:lt,lll.iiiiuliy iY i}

:t--tl:1)dSjrtt' i)ti.)" L- Iiii.i.j riC t'ItIImiii, II .1w a-.t m 'I1

ri. ttc. Crit bus .iii1ii'liuf .1 Ce'',tJ-iwwr e,mmre -lilt_c.

'J 1n,.Jç mit''l tillili iii. .artl für a _{incie-i.ü. -r} vt

- . .. : .

...

-.---- - - ,.

-;.:'j

'-.s,s-'

t

_I

c..

/

/1

-

LL'i.±

'

f)Y i(i: ll-.s 3. itt4

j

tzr :)

t- .--,

s

;:;'

.. l_\i;i .'II.Iu. \' -. r

-.,

I

t:_-

_-:-

-I _{,.:-*.'_____.--.}ttt: \__

Ifvou

jt your advertisin

to reach industry and

government leaders in Iral\ reach for SCIENTIEIC

AMERICAY's Italian edition, LE SCIEYZE.

Toda

Italy represents a country dat has mastered the

tinest points of high technology across the 1il1 spectrum of

industries. The people responsible tor Italvs achievements

on the tcchhology front arc reading LE SCIENZE.

If von \\ant to reach Tons' Severn for derails, conta:

LE SC1ENZE S.p.A.

Via Del Lauro. 14

20121 \idano. Italy

Telerthone (011) 392-S05-894

) )O. 63% 14% I

:ctrs br :un:.

nccr'.ft

i :...ien much a '.vc.cd ruic t

rue-ui: cle. 1 ne ttat

C the v:- ;.

fl tuet. a

:uOJ:e(t Ok'. cL

r;':,:' 1,..':

ii

d Joped a a

:encrnent ol' th., rirst crsort of our

craft. \'.'e

:tLd 1gh:. eiaht

pon-:oon floats tot: the hare :ttt an

an-:s,ited tukeo:T e aId Lu.' m.d-e t'ra:u a s:anistill. This proved to be possible, and with practce acceleration from a

stnadint start to the fuhv foil-borne

mode took oni three seconds. The

craft ako became much more

prac-tical because it could now "land" on,

as well as take off from. its floats. (The catapult-launched Fi,ing F1s: I gave the rider a dunking whenever

he stopped pedaling.)

Aboard the F!fitg Ffsh If one of us (Abbott) recorded a time of six min-utes 39.44 seconds over a 2000-meter course from a standing startabout 10 seconds faster than the single-person

rowing-shell record. From a fl ing

start the hydrofoil watercrafr also was

able to sprint 250 meters in SS.46

sec-onds, reaching a maximum speed of anproximately l knots.

The

revolution in human-powered rec-time is ripe for a technoloical

reational watereraft. Laser

In:erna-tional has just tntroduccd the da1lard,

a partially enclosed. seaworthy boat

designed by Garr'. Ho Several new

pedaled catamaruns and proas (boats that have one main hull and a small-er stabilizing outriessmall-er) otTsmall-er rough-'.vater seaworthiness and impressive speed. Jon Knapp of Saber Craft has designed and built a oropeller-driven proa that is faster than a shell in rough water but, unlike a shell, requires no special skills to operate. The

Dorvcv-dc, a propeller-driven single-hulled craft designed by Philip Thiel,

pro-vides good load-carrying capacity at

speeds twice that of the rowed dory

from which it was dertved.

\Vhether or not hydrofoil craft

be-come popular for recreation, there

seems to be little doubt that they will flgure prominently in the next round of breaking records. The international Human Powered Vehicle Association encourages competition in human-po'.vered vehicleson land, on sea and in the airwithoe: :inv arbitrary Itmits placed on their design. Such

competi-tion will push the SPCS. of

human-no's ered h\ drofii craft c' higher. It

is not farfetched to en-. i:on such craft reaching speeds as high as () i.:nots_

one and a half :imcs fast us the

speeds ttLitned 1:. T'it'm' I! and

sia:ñca',tl

faster titan 'he :ecds

at-taincd by

cme sl:chs uc:erec h

thletcc carmert.

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