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_ : AMATEUR YKCHT RESEARCH SOCIETY HERMITAGE, NEWBURY, BERKSHIRE.
CATAMARAN DESIGN A . Y . R . S . P U B L I C A T I O N N o . 1 5
JUMPAHEAD
C O N T E N T S
I . The Modern Catamaran. 7. The ROECAT. 2. 12 Catamaran Design Features. 8. 12-foot RIVER CAT. 3. The PI-CAT. 9. GEMINI. 4. The Y V O N N E CAT. 10. The ICfoot CATAMANNER, 5. The QUICK CAT. I I . An lnflntnbla Cntnmnrnn, 6. JUMPAHEAD. 12. A Cntnmnrnn Cnprlxr,
P R I C E 7 5 c e n t s P R I C ~ A / .
i BUILD YOUR OWN CATAMARAN i THIS WINTER
-1-here is more to a s~~ccessful C a t a m a r a n t han just t w l n hulls. O v e r five years' experimental work culminating in 5 e v e r e tests have produced the I'IIOUT Shearwater C a t n ~ n a l - a n wl~ich has sailed w ~ t h 5 u c h o ~ l t 5 t a n d i n g results that over 700 sail numbers have been registered in the new
Class.
Why not build you r own ready for next s ~ ~ m m e r ?
PROUT SHEAR WA TER 111
i
and 14' 6" SWIFT 6 3 .a"
CA TAMA RANS SHEARWATER I11
SHEARWATER KIT complete less sh i.: £ 129-16-0
complete less sails : £214 Ex Works.
SWIFT 14' 6" CATAMARAN coniplets less sail? : £165 t x Works.
All kits are complete with all fittings. and sunnlied with hulls
. . -
jWlFT KIT complete less sails : f98 A
mouided. sdnded for nalnt. /m Photograph by yur t e sy qf
Lillipu! rnagazlne
G. P R O U T & SONS LTD. THE POINT, CANVEY ISLAND, ESSEX. Talaphona Canvay 180
This publication deals exclusively with the double 1111l lc~t l cl-aft. I t doesn't seem lvorth while any more to try to give " C'ar;~l~~;~r; ln " its original meaning and, in future A.T.K.S. publications, \ \ . i l l be used for thc equal hulled craft. " Outrigger " or " Tl-irn;ir;~lr " ivill bc used for the unequal hulled type. However, it inust still be remembered that the Indians and other people will still call their outriggers " Catamarans " as they have done for many centuries.
An attempt has been made here to give the main principles of catamaran design, so far as these are known. No douht, sonle of thc conceptions are controversial and articles giving other points of vie\$ will be welcome for future publications.
\Ire arc lucky to have an article by Arthur Piver of San Francisco on his elegant catamaran, as he has had a lot of espcr~cncc with both catamarans anci trimarans and has made escellent c \ ;~~r lp les of both.
This study is not complete. \Ire still nccd to knoiv the rc la t i~c performance of :
1. Catamarans with sections of a right anglc ;I( tlrc keel.
2. Catamarans with symmetrical sections of ;I tlccp ellipse resembling those of Afanu h-c;i.
3. Catamarans with sc~rli-circular sections and a bow overhang likc that of Gemini.
Relatiur S teeds .
It is yct to be sho~i-n that any small catamaran anywhere is faster than the Prout Slzenrwc~ter [ [ I . I%ob Harris' Ocelot beat one Shear- ,water [ I I in 1,ong 1sla1:cl Sound in a strong wind, though thc smaller craft was faster in light going. 13ill O'Brien's :~ron/)c~l~c.ocl is similar
in speed rcacliing and running but \\;is slower to windward i t i 1 1 1 1 .
races this year (1057). Twin C'.l3.s ant1 rnore racing cspcric~rc~c might make the craft rnore similar. 'l'llc Ilustralian Yco~lne , bcilig 20 feet long, may have similar spcetis to a Sheurzcuter ZII in stroiig winds but is likely to be slower when the \\.in& are light. 'To rn!. kno~vledge, no contact has been made bctwccn tlie two as yet.
Arthur Pi\-er's Pi-Cat should be similar or faster than Sl~rarwat'r because she is longer and of the same basic design.
All the other designs i n this publication ivill bc slowcr than Shrarzcuter 111. Naturally, the shorter craft will be slo\ver hut they have to be beamier to carry their load and thus I~egin to lose the slim hulls which give the catamaran its speed.
T h e majority of yachts built no~vadays, some of them costing many thousands of pounds, ]lax-e not had even the most rudimentary tank test done on a model first. Indeed, not many yacht designers have even thc simplest testing apparatus of their own. This may have been the normal practice in t l ~ e past but, in my opinion, no yachtsman should eerr have a yacht built itz future unless a model has been made and compared with a model of a comparable nature in a test tank of at least the quality of that described in our publication No. 12, .-lmateur Research. Such a tank could be made for such a small sum of money that it would be a very reasonable thing to ask.
'rhis matter has been brought to my attention recently because of the numbers of people who have asked me to design catamarans for them. Now, though I have designed Gemini, which is described in this publication, and it goes well, I have never thought of becoming a professional yacht designer, even of catamarans, because I would like to know exactly the qucrlitv of the craft I am asking people to build. I could only find this out by some test and this I have not yet done. 1 consider that, to take money from people for a design " because it looks right " is prehistoric behaviour and people should demand much more from yacht designers than that, nowadays. T h e best yacht designs have always been the result of testing and the best yacht tlcsigncrs have always done tests. W e should insist that this become tlic usual custom, rather than t h e exception.
I'l-ofcssor Ata Nutku of Istanbul, 'L'urkcy is prcp;rl-ctl t o It.st C ; I ~ ; I I I I ; I ~ - ; I I ~ iiiodels sent to him. I>ct;iils of t11(. size 01' ~irotl(~ls (. ( 1 1
cot frotn tlic lrtlitor.
T H E 1,ONDON BOAAT SHOIV
A Stand has again been taken for the neat 1,ondon Boat Show. This year, exhibits will be full scale as far as possible. Our stand will show ( l ) a non-commercial catamaran, (2) the A.Y.K.S. catamaran with Melagasy floats and hydrofoils, (3) one or t\vo " \.\'ingsails " and (4) Dr. navies' canoe Swan c!f .Ardrn, to show the possibilities of " Developed plywood " design. IVill any members with devices, models or full scale craft which xvould be suitablc for sho\ving, please get in touch with the Editor. Our spacc is very limited but \ye \\.ould like to put on the best sho\v pc?ssible. It n.ould he nice to havc the " W i n g " foresail, which is shox\-n on Page 25 of \V.'TNC;S;\II,S. on the catamaran instcad of its jib. If anyone would like to rnakc this for us, the dimensions can he got from the Editor. It is siinl>l!. a matter of making an elliptical shape with batten pockcts ever! IS inches. N o bolt ropcs n-ould be necessary and the cloth used 11r. t . t l
not be expensive. We will again need to have people on the Stand to kcrp 1I1r
public talking and interested in our work. T h e Boat She\\ I I I I I S
from January 1st t o the l l t h , of \\ hich I can only manage to Ilc 1111 I(.
the first four days. Mrs. RIor\vood, will honever, be on thr 51.111~1
the rest of the time, and given somc relief, tv. i l l doubtless I ~ ~ I I I . I S ( . I I I
her usual capable manner.
'I'HE M O D E R N CATAMARANS
I t is very obvious that all modern catamarans o\\:c their ( l ( . z i c ~ ~
and existence to .&fanu Kai , designed by II'oody I3ron.n ant1 I I I ; I C I ( . by him and Alfrcd Kumalai in Ha\vaii after the last \ \ ;II-. '1'111s wonderful craft is described in our publication AMERICAN (':l'I'.L MARANS from nihich the two dra\vings havc been taken. S ~ : I I . ~ I I I ~ with this design, the relationship of many modern cat am;^^-;~ns \ \ i l l be studied.
Manu Kui T h e basic idea of Planu K a i was to produce lateral rcsist'tncc
from the hulls themselves so as to avoid having a ccntreboard or lin keel to prevent leeway. T o achiel-e this, the hulls \Yere asymrnctl-ical with the flatter sides on the outside so that when sailing : ~ t :In angle of heel, the lee hull should produce a force acting to n-indtvard. 'I'hc windward hull would be less immersed and hence ha\rr less effect in producing a force in the opposite direction.
It might be wondered ho\\ such a concept could arise in the rnind of any naval architect, amateur or professional, stecpetl, as \VC
all are, in the traditions of \\-cstern European boat building ancl ideas. T h e clue lies in the shape of the section \vhich is exactly that of the large native Micronesian " Proas " some 60 feet long so ably described by Hornell in his book " THIC CANOES OF OCE.ANI.4 " published by the Bishop Muscum in Honolulu \vhich specialises in Polynesian and Pacific Island culture. T o me, it seenls \.cl-! obvious that these hlicronesian craft \Yere studied in great detail before l M a ~ ~ u Kai ~ v a s designed. T h e large Polynesian \ \ a r c;tnocs so ably tlescribed by Captain Cook most likely had semi-circul;~r sections, in common ~ v i t h all Polynesian canoes and outriggers of \\lhich we kno\v. 'I'he only place in the \vorld where the conccpt of asvmmetrical hulls ever cxistccl \vas in Rlicronesia ;lntl to .I Icsscr extent in Melanesia.
Munu Kui was thus the fusion of the 3licroncsian ;~n t l I'olvrrcsi;~n cultures as far as the shape was concerned, combined \\.ith hlrrcl-ic;~n and \Vestern European constructional methods. One fc;~turc \vllich resulted \vas the canoe stern of the hlicronesian origin;ll \ \ l r ~ c l ~ is to he found in very many of the ~notlern catam;lr;lns tl(.\iq~rc.tl \ \ ~ t h \lnrtz~ Kai in mind.
Creger's main idea \vas to protlucc easily constructcxl c.;ll.llrr;lr;lns by the usc of ply\vood sheets but of the same hasic s11;11>c ;IS t11 ( . s1rc.c.c.s~- ful .Manit Kai. H e also used asymmetrical hr~lls ;111(1 (.;1110(. sterns
but, though his craft were often fast on a rcacll i l l ~ l r c . I ; I ~ ~ ( . I - sizes, the tlccp box-like sections did not slip tlrror~glr t l r c . \ \ ; 1 t ( . 1 - l~k( . \Icrttrr
Kni and, 1 suspect, often protlucetl etltlics ; I I - O I I I I ( I OI(. (.lli~r(.s \ \ , l l i ( . l i
rnust have slo\ved them tremendously.
~ ' / z P 7 ' c h ~ t c / t ~ t Hulls
'I'hese hulls. \vl~icll \.ictor ' l ' c l l ( . ~ c l ~ c ~ IISCS i l l I~is 'I 'rin)ar;~~)s ;~lso takc origin from .Ilotrrr \ - i ; ~ tlrc 1,ccrr- ( ' c r i , I)ut t l ~ c y ;IIK o f mllcl) less depth than those 01. tlrc 1;lttcr. In I;lct, they re roughly half scluare in shape, \\-hieh is a torm \ \ i th rel;~ti\rcly little \ \e t ted surfacc \\hieh e\pl;~ins the speeds ot IS knots \\hich have hccn achie\etl. 'I'hcrc rnust he somc edtlping around the chines \ \hich \ \ i l l slo\\ the craft in light \\.in& but this is obviously of much less importancc than in the I,c,ur ('cri as Victor's 'l'rimarans have a good perforrnancc In liqht \\intls.
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up. 'rhis is due to the fact that the bow n-ave is o\.errun by the speed of the craft and it is raised by flotation in its o n n bow \\-avc.
'L'ruc planing is due to the dynamic lift caused by particles of water hitting the underside of the hull, lifting it u p so that i t rides at a higher level than \\.hen it is stationary. Dynamic lift must ccr- tainly occur at the boivs of the chincd catamarans, hut olving to thc I O W ratio of beam to length, not enough lift nil1 occur along the \vliole length of the craft to constitute true planing at thc spccds \vhich have 1)ecn achieved so far.
I'crhaps our greatest ignorance about catamaran hulls is to tlo n i t h their " Fineness." \Ye do not know the best ratio of lcngtlr to h a m . Neither do ivc knou the optimum " Prismatic coeficiellt." 130th of these can hc found by the long process of trial and error at full scale or much more cheaply and quickly by testing models.
'This is a figure \vhich gives us an idea of hot\ full thc c ~ ~ d s of a yacht arc for a given maximum scction. It is arrived at h\. ~rlultiplying the area of the maximum scction by the naterlinc length. 'l'his gives us ;l volumc, and the ratio of the volume of \\-ater displacctl h!. the 1)oat to this volume is the prismatic coefficient.
\Yhcn the prismatic coefficient is high, thc cnds of t l ~ c I)o;~t arc full and the light wind performance ~vill be good h e c ~ u s c tllc \\.ctted surface \\;ill be less for a given displacement. \\'hen tllc prismatic coefficient is lo\\., the ends of the boat \\.ill be fine antl, tllougll l igl~t wind performance may be less good, the strong \\incl performance may he better.
.\'/~eur-zcat~r. I I I has full cnds \\-it11 a prismatic cocficicnt of 0.6s. Ocelot, \vith fine ends has a prismatic cocficicnt of 0.-57. 'I'hcsc t\\.o designs seem of equal merit to Inc. 'l'llc fact that, in a trial bcttveen the two, ,'ihrurzccztrr IT1 \vas faster in light winds, \\hilt Ocelot was fastcr in strong tvinds, is exactly \\hat could be expected from thcsc cocficicnt figures.
" I7l!ingv a hull is amusing and even exciting. Honc\e r . in cataniarans such as Shearwuter, Rob Harris' Ocelot and many others. this put too much displacement on the Ice hull and the craft is slo\\er than when thc displaccment is more equally spread hettrecn the hulls.
Ho\\ever, in :)'~rtt~pukr~ut/ ancl (;~ttritri, \\.lrcn one llull lifts otf the n;iter, the spcctl increases, instead of falling. 'I'he reason for this is hard to produce but it may be that the forward overhang gives a greater overall sailing length n-ith the same fine entry as when they are o n both hulls. \Yhen other catamarans dig their hulls in, the entry hecomes much more bluff.
\Yhen sailing on one hull, the transonl I~ecomcs more deeply inlmersecl in Sheurwater. In the t\vo above craft, the flat floor aft might keep the stern raised and the transom from sinking so clreply.
Almost without exception, the top speeds n-liich hare been measured reliably for well designed catamarans and trimarans have proved to be bet\vecn four and five times the srluare root o f the water- line length. T h i s again is further evidence that catamarans do not plane because hulls like those of :l/futrri h-ui certainly \vill not plane. If any catamarans (/it/ plane, their top specds \\ould be greater than those of those which did not.
Slim hulls and hulls with a \. section should bc tried to see if they have a higher top speed than the semi-circular sectioned hulls.
f3elo\v 1 I , knots, the semi-circle \\.ill, of course, be the best and the only problem, therefore, ~vhich is left is to find out if another shape will be better at specds in excess of this.
Catamaran manoeuvreability depends as in other craft on the underwater profile. However, they always nccd to be sailed the \rhole time from one tack to the other not only because they arc relatively lighter than other boats but also because the hull shape is such that it has good directional stability and tries to run a straight course at all times.
I t is essential, therefore, to sweep the keel line of the profile u p to the waterline both for\vard and aft and to provide a centre board or tn-o centreboards around which the craft can pivot. Hoth the Prout Shear7rtat~r and Gemini are much harder to put about without the board than with it.
Catamarans n-ith asymmetrical hulls such as .Ma?rrr Kai and the I.our C'ut arc harder to put about than craft with symmetrical hulls. I,ong straight sides also make manocrlvrcing difficult which is probably the reason why catamarans of the " Split boat " typc have a poor reputation for putting about.
I t appears to make little difference what shape the keel line is as long as it comes to the \vaterline fore and aft. It can be elliptical in shape as in the Shear~~wter or lvith an almost straight line from a deepest part for~vartl of midships as in Gemini and still manoeuvre well. T h e position of the centre of buoyancy also can be put where convenient so as to balance the \\eight of the cre\v and craft. If i t is far forhard, as in Gemini, the crew must sit for\vard in light winds but come aft for high speeds.
It is almost axiomatic that a fast craft \\.ill I)c \vet and a catamaran is no exception. Ho~vever, the catamaran has one aspect here not possessed by other Ijoats. 'I'hat is that the \\.eather bo\v \vave of the lee hull can rise up and produce a jet of water of large dimensions dircctly on the creu on the \\-eather side. This is decidedly un- comfortable.
Spray deflectors, such as are used with speed boats are non- being fitted t o the Prout S h e ~ r z ~ a t e r and are helpful. 'I'hey consist of a batten of triangular cl-oss section with a horizontal lotver surface. \Vater being scooped up by the bo\v hits the batten and is shot outivards and does not rise high enough to come aboard. It has been shown hy Professor Ata Yutku that these spray deflectors gii,e increased resistance in the test tank but in practice, this is probably morc than rnade up by the lesser \vater carried in the cockpit.
It is also possible to deck in the \\.hole forward part of the craft betivee? the hulls but this appears to trap air and to slo\\- the catamaran very much. Ho\vever, by studying the air flow forward, it should be possible to design a fore deck bet\veen the hulls ~vhich does not obstruct the ail- flo\\ hut still keeps the water do~vn .
.Ilat~li h-cti hacl a canoe stcrn. I bclicvc that this \$as simply because she took her origin from the llicronesian canoe more than from the Polynesian outriggers or large war canoes hich often had counters. All the craft which o\\-e their origin to .Ilanu Kai directly seem to have copied her canoe stcrn, except for the English catamarans W-hich have the Europeanised Kayak transom stern of the Prout Skrcrr~catrr. It is therefore ivorth ~vhile consiclering \vhich stern is likely to be the hest.
r 7 I he canoe stern has the ad\-antagc of being streamlined and hence has less wind resistance than a transom. It is usually morc attractive t o the average yachtsman than the transom bec;~use it con-
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by a wave ; or at least h a i r to jump 01-cr it. 'I'hey sutfer neither indignity. f~lo\vever, when they have penetrated far enough into a wavc, buoyancy gets to \vork, unless they are too slim and deep, and they bob up like corks, thus once again achieving their clesigned state of surface travel.
'I'his behaviour of catamaran hulls (of good clesign) nieans that their motion to small waves is less than that of a beamier boat.
In larger Lvavcs, the catamaran will take the main contour of the wave which is a surprisingly gentle slope, even in soundings, and it is found that on the dcep seas, the motion of a catamaran is very easy indeed, compared to conventional keeled yachts. 'I'hc reason for this is that a catalnaran \\.ill only take the slope of the wave whereas a keeled boat will havc a pendulum movement which will oftcl1 cause it to heel at t\vice ancl even more times the angles of slope of the waves. For example, a keeled boat running down the trades will often indulge in thc tactic of " Rhythmic rolling " \\-here the frecluency of the yacht's roll corresponds to the period of the Ivaves. 'I'his cannot happen to a catamaran.
.A catamaran Ivill have far less motion and be far safer at sea than a convcntionai boat of the same size. As rcgyrds safety, this point is arguable in the case of cruising catamarans which can I,e capsized and or?': must keep an open mint1 about thcm till \\.c havc more information.
1,igIit catam;irans can all I I ~ capsizecl. \Ye have an intcresting account of one capsizc later on in this pul,lic;~tion tvhich was not righted but, usually, a light catamaran like Sh~~r~rnccltrr 111 can be righted by her ere\\ should she be allo\~ccl to tip u p . According to Jack Blundell, capsizes fall into t\vo types :
1 . With the board lonered. 2. \Vithout the dagger board.
In the case of S o . l , as the mast hits the \Later, the helmsman should slide over the hull onto the board, immediately. This nil1 oftcn stop the craft from turning further and halt it n i t h the mast just below thc horizontal. T h e creM should then frce all the sheets and hand the jib sheet to the helmsman. 'I'he helmsman shoulcl then lcan out\vards, using the sheet to hold by, \\liilc, at the sanic time, the crcu lifts up the mast as mueh as he can. .As soon as thc
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.ilq[uassv jo aw!l aq, ~t! Isay a111 uo ~ay~0.i ij~: put! amj aq~ jo Iaap poo8 E ;iu!~eu!u~!la .icl ierl.uaulos uY!sap aql a;iuer[~ p!p I q8noq1le 'r~!~ldxa ,ouuer, 1 l3g E 'asucrn~oj~ad rl! .io!.iaju! .it!j s.ia.41 slnoqea~arl ssndrl .iaqlo '.ia.\a.\\olj ..iaqlea.\\ ,q8!l U! ~da~xa 'iJu.iol~ aq1 put: I~?uo!Jwu.'")~ aql SE sadh palunc.\ q3ns 8u!pnl3[1! 'JJEJJ ~TL!S.II:~!UI!S .iue .>aedjno plrloa pu!.\\ aq~ uo pue 'pu!.\\ aql
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.dn Le.\\ ~qB!.i S! aqs uaq.\\ s.\\ocl aq, una.ulaq aq uaq, II!M a~ .sll~j l! se w!q I![[ ~'usaop I! ~eq, os p.raninr,j. llnq ~addn aql .iapull y~np jsnlu uewswraq aq, 'dn .ie.\\ ,q;i!.i yxq dold ol Lpea.i 'aJut!leq jo iu!od aql isud jsnr R! III?.II?ILII?~I:~ JIIJ ~UI? .iT))E.\\ ar11 a.\t!al I!RS pue ]sew
The 20' catamaran Pi-Cat, designed by Arthur Piver, Mill Valley, California
boat would squat just before coming into the eye of the wind, and under these conditions it would not respond. Also, if there were more than three persons aboard, the craft was just dead in the water, unless it were blowing a young gale.
I also spent quite a bit of time aboard a 20' catamaran com- mercially manufactured over here, which had the worst hobby horsing habits I ever saw in a boat. This craft, although it manoeuvred well otherwise, spent most of the time just bobbing up and down in a most annoying manner. If it would come to a single large wave, for
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\vetted surface, \vhile the only \vay I could think of reducing the hobhy horsing was to have no fore and aft rocker. 'I'his latter step also gave more hnoyancy forward, \vhich did indeed eliminate the bow hurying.
Being my first dcsign, and not being sure of my centers, I devised a track arrangement between the hulls, so that the single center- hoard, which was fastened to a stout aluminium pipe, could move . fore and aft. 'The original idea \vas to have a trim tab arrangement in the cockpit so that the board could be moved easily, but I never did get around to completing it, as the hoard proved insecrlrely mounted o n the pipe, and indeed it twisted almost like a pretzel, even though composed of a " ply. 'This lead to fastening it more securely through the centet- section, but at least I had discovered the best point for balance.
Incidentally, here is an area li)r morc research, for 1 l,elieve that 'I readily moveable board \\.ould be a distinct advantage for a catamaran, as \re have discovered that the best way to come about in this type is t o sail it around, and the application of the rudder too soon in the rnanocuvre \\.ill kill the turn in sloppy conditions. In other \\or&, when the boat is close-hauled and it is desired to come about, the rudder is released \vhilc the trim tab is actuated tti give the craft a strong \yeather helm. \Vhen thc boat reaches the point \vherc \vind begins to spill out of the sails, then the rudder is applied to continue the turn at a steady rate. Incidentally, \\-c always pull the boom nearly amidships as the boat approaches the eye of the \vind, main- taining drive as long as possible. \\'hen the rudder is finally applied, we find that the angle should be increased as the speed diminishes, a l t h o ~ ~ g h never morc than 45 degrees.
.\Ithough the single centcr board seemed to pro\-icle sufficient I;~teral plane, I later replaced it by a board in each hull, and to my surprise discovered that although their combined area equalled that of t h r former single board, they were markedly morc efficient. 'I'his phenomena was later explained by an article in an A. \ - .R .S . publi- cation, regarding tip losses.
'I'he hulls arc semi-circular bclo\v the chines, {vith the full chine- heam carried relatively far for~vard to provide sufficient buoyancy so that the hotvs \\.ill not bury. 'The over-all beam chosen is just bclo\v the maximum for trailering on our high\ \ .qs . Construction is largcly of l" ply\vood, \vith the sections belotv the chines of 1" square strip-planked spruce, covered n i th one l a e r o f mcdium- \veight fibreglass to just above the chines.
.sayvl l! leq.11 n.\eq lou saop .i[dm!s ~sdd!ys a;lr!~a.ze nql 'suo!l!puos auIaJlxa Japun ua.\a 'a1qno.u ou aAeq [l!.z\ lay jo asuas poo8 e 141!.\\ .ropes u. q8noqqe put: 'il!l!qes~.\naoueur jo yssl aql S! ad.il ueJsrusles ay1 ol des!pueq jay aql lcql a.\a!laq 1 '~EJJU-?~ U! .)suelsn[al sqqnd jo ap!slno 'lse1 jo .I~I~KLU e sv
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T H E YVONNE CAT
L.O.A. : L.W.L. : Beam O.A. : Beam, hull ..
Draught : 6" Sail Area : 190 sq. ft. Weight :
This catamaran was designed by C. H. and L. N. Cunningham of Victoria, Australia as a series of modifications of a hard chine catamaran with box shaped sections till it became the elegant craft shown in the drawings. All this was carried out full scale and started in 1952 and the craft took its final shape in 1953. For the Cunning- hams, this was the only way to develop their craft because they had
T w o Yvonne Catamarans.
so little to go on when they started. Their development had to be carried out almost from the same point as the other catamaran pioneers.
The first catamaran with box shaped sections was well rockered on the keel to allow of easy manoeuvreability, had symmetrical sections, a canoe stern, a central centreboard and balanced rudders. I t was
very fast in smooth water but in rougher water, the fore and aft stability was not enough and the rudders lifted clear at times and the flat floors pounded. As a result the bows were extended two feet, lifted and flared, a false V-bottom was added from the bow to amidships and the rudders were enlarged. This cured all the faults of the previous
An Yvonne " Flying A Hull."
design and all the present Yvonne 20 catamaran owners feel that they have a very satisfactory craft. T o day there are 10 Yvonne 20 cata- marans registered in Victoria, with 87 sets of plans sold all over the world.
Performance. The Yvonne 20 has sailed over a mile distance at an average speed of 18 m.p.h. In bursts, a speed of 20 m.p.h. has been exceeded. Over a distance of 21 miles in very rough conditions, 15 m.p.h. was averaged on a broad reach. It will be noted that these speeds are almost identical with those of the Prout Shearwater, Ocelot and others.
Dengn Features. As compared with contemporary British and American catamaran design, the main features of the Yvonne 20 are:
1. The forward overhangs. - 2. The taking of the torsion strains between the hulls by two crossed
girders instead of the rolled plywood system of most designs. 3. The ingenious centreboard design, which allows the board to
come up below the cockpit when it is up.
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/,;y/tt l r7;t11/.7 In light airs, the crc\\ moves \\ell for\varrl to lift the transom
clear of the \vater to reduce net ted surface. Sailing :~uumpu/tec~d at 1,ymington this year, Richard Creagh Os l~orne \\on a four hour drifting race against a .inS.
7'0 Il~.indzctrrr/ bnzprrh~ud gives of her best at 40 to the apparent wind ui th
the sheets \\-ell in. She goes to the windwarcl \veil by luffing to each gust \vhich makes the Ice hull bite cleeper, and for cruising the centre hoarcl can be dispensed \\.itll.
I't~ttitrg About IVith practice this can be done in 5 seconds, but, as \\it11 other
catamarans, the technique is different to that used \vith dinghies. T h e jib should be held in hard until it is on the point of " backing" but definitely not " aback." It is then changed o \ e r and shceted in fast on the other sick so that it is dra\ \ ing her fortvard. Catamarans 'ire generally light craft and, on coming up into the \ \ ind n i th a large sail area, the flogging sail and the seas tend to drive the craft back- u a ~ d s so the sails must be kept dra\ \ ing to the last possible moment. .-l rong impression is also given I,y the change in speed \\hen putting about. .l rlingliy slo\\s d o n n from about h knots to 2 o r 3 knots \\liereas a " cat " may be tloing 10 or 12 knots and slo\\s clown to the same spcctl ;IS the clinyhy \\ hen putting about.
Flyitlg U 111~11 \\.'hen salling single li.r~lrlcrl \\it11 J~tmpuhrcrri, harden~ng thc
sheets 'lncl lifting one hull about a foot off the \\ater in a 12 knot n i n d incrrc~ses the speed from 15 knots to 17- I S knots. This is due to decreased wetted surface of the \leather hull, whilst main- taining sufficient dynamic lift on the Ice hull.
Sp~rr i s 'The highest speed recorded by the Smith speedometer, carrying
l67 sq. ft. is 10 knots, in 2 ft. seas, cren sitting inboard. ideal con- ditions, i.e., strong uind and smooth \later, are eagerly a\laited.
There arc some objections to catamarans put for\\ard by peoplc. \\hich Hill O'Hricn nould like me to state, \\ith his ans\\crs :
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Gemini.
The Layout The general layout and dimensions are those of the Prout Shear-
water 111 as is the bridge design.
Hull Design The hull has a long flat run with easy twisting of the bottom
plywood. The chines are on the waterline and the keel line is rockered
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cost ;\latcrials for the 14' ('nturnclnnrr should be bought for ahout
k:75 including sails.
'I'hc plans and instructions for building consist of sixteen largc sheets, containing over a hundred detailed step-by-step dran-ings. 'They may be obtained from 1'. J. n'lanners, 93, Ridgen-ay, \Yestclitf- on-Sea, Essex. Price 50, -.
'1'kII: IS 1;'I'. h IN. H I G H SPEED CATARZASNER
.l larger version of thc 14' C'utattzurrner is no\) being huilt b> 'l'\\ in Hulls I>td. to 1:. J . R/Idnnersl design.
, l his craft is an esperiment to~vards a light, easily stored, transported and launched sailing cataruaran. So far, i t has only been used \vith paddles and an outboard motor on the Thames. It consists of tn-u light inflatable floats 14' long by 15" in diameter, joined by a light wood, aluminium and canvas framework. Each float consists of tn-o separate parts (1) a rubberised fabric lining, and (2) a heavy can\.as outer cover. IVhen collapsed, both of these can be rolled up into a bundle about two feet long by fifteen inches in diameter. '['he total#\\-eight of the craft is 50 to 60 Ibs. without motor.
Each lining is divided by a partition into t\vo equal compartments which have to be inflated separately. The linings can be used on their own n-ithout the outer covers but, of course, they will not stand such rough treatment as the combined inner and outer. They are designed to take an internal pressure of two pounds per square inch, \\-hen they are surprisingly rigid. Much less pressure can be used in calm water. They weigh about 6 lbs. and \\-ere made by Elliott Icquipment, I,td., I.lympia, S. \\-ales.
T h e outer covers arc heavy green flax can\-as, liberally supplied ~vith attachment points for the frame\vork. 'l'hcy \vcigh about 0 Ihs each and \yere made by C'. Nielson and Sons of I<ingston.
Tom Lancashire's Inflatable Catamaran.
The Framework The framework is made up of four aluminium tubes, each 6'
long, running fore and aft, two over each float. They are clamped to two transverse members (1) a strong built-up beam aft, and (2) a 24" by 14" spruce member forward. Four wooden poles, 1" in diameter extend aft from the tubes to help spread the load on the floats. The strength of the framework is in the built up beam. I t is not very rigid at present and for use in choppy water, it will be made either more flexible or stronger.
.4ssrrnh/j~
T h e assembly sequence is as follons :
l . Place the aluminic~m tubcs in position in the clamps on the trans- xerse mcmbers and tighten the clamp bolts.
2. Insert the wooden extension poles in the aft ends of the tubes.
3. 1,acc on the canvas sling.
4. Inflatc the floats.
5. Position the floats under the tubes and lash in place. T h e forward ends of the tubcs fit into pockets on the floats. A single lashlng is used round the aft end of each tuhe.
Inflation
A racuttm cleaner gi\es the quickest inflation of the floats hut if one is not available, an ex-Air Force large dinghy bellows will do. It then takes about a quarter of an hour to inflate all four compartments. One pair of lungs takcs a bit longer. After being left inflated for seleral necks on one occasion, the floats of my craft still had enough pressure to be used without topping up.
B u ~ L ~ UP e r ~ n /.-- ~ -
orrnoaeb o a a t r r i -- W E @ " " CS..""S OurGP COVE*
Motor
T h e outho;lr-<l ~ I ~ ~ I I I - ~isc.cl is a Seagull Super 40 (11-24 t1.p.). At half throttle \ \ i t 1 1 o t l c . up, it gives a speed of 5 to 6 m.p.h. A4t higher throttle o l > c , ~ ~ i ~ ~ g s , ~ h c speed increases I,ut cavitation of the propellor p r o d ~ ~ c c s ~)c~-ioclic. jerking of thc \vhol' craft. An attempt will be made 10 c.111-c, Illis later on.
'The ~ ~ ~ o t l i l i c ~ ; i ~ ~ o ~ ~ s for sailing have not been quite settlecl yet t ~ u t thcy \ \ i l l l > ~ ~ i ~ l ) : ~ l ) l y i ~ ~ c l u d e : -
l . A sl,ort I I I ; L S ~ s ~ c p ~ ~ e c l at the centre of thc craft. 2. JCs~cn<l i~~g I I I C I'~-an)c\\ork further aft. 3. I,cc I)c~;~l.tls ~ ) i \ o t c d in a cross tube. 4. A si~rglc I K I I ( I ~ I ~ I - 011 an cstension of the frarneivork.
111 : \ I I I ~ . I - ~ C ; I , (;oodycar rnake " Airrnat," a double surfaced in- flat:~l>lc. ~ ~ ~ l ) l ) c . ~ - i s c d nylon rnaterial \vhich can be used for structures. 7'he I \ \ . ( I S I I I - ~ ; I ( . < . S are Joined by thousands of close pitched nylon fibres ; I I I I ~ , \ ~ I I C I I inflated, it can s tand high air pressures. Goodyears say " I t 111.1l<c.s like 3 beam." I t sounds excellent for an all-pneumatic c a t a r l ~ : ~ ~ - a ~ ~ ; I I I ( I possibly for cantilever aerofoil sails. Messrs. Frank- enstci~i A SOIIS , i'ictoria Rubber \Vorks, Manchester 10 can supply a nylo11 I ' ; ~ l ) ~ - i c . I>~.oofed lvith "Neoprene." 'This is said to be an iniprovc.1111.111 0 1 1 rubberised cotton fabric in respect of : - ~
(a) I<cs i s~ ;~~rc . (~ 10 oils. (b) lic.sis~;~~ic.c 10 sunlight.
(c) 1 Ixc i11~. (cl) \Vc;11. ;111<1 tc;ll-. (e) S t r - c n x ~ l ~ I o ~veight ratio.
,4 CA'TAMAK.4N CAPSIZE
by OWI:.N DI~MPI.ETON
'I'hc " C'at " \\.as lying alongside the Icc side of Rochcster Cruising Cluh pontoon. \Ye had been doing the various odd Jobs \\ hich are alivays needed in a new boat and nocv it \\.as time to go horne. 'I'irnbcr for the rubbing bands xvas aboard and lashcd do\\-n and all sorts of gear had been sto\ved in the hulls. My buoy \vas on the wind\$-ard
side of the pontoon and the wind n a s force four. I had no motor. T h e ebb tide was running at 2 to 3 knots ~ j i t h the m ~ n d .
lIazel, my crew, decided that it was too rough to sail but I put my faith in the man who told Ine that a S/~earwater had never been known to capsize and I got under way alone.
1 set the close reefed main only and all went \yell until I was in mid stream. 'I'he wincl then suddenly dropped away to force 1 and I was carried down strcam towards Rochester bridge where the tide runs at 3 to 4 knots. I rounded u p and dropped anchor but the \vater \\-as cluitc cleep and 1 lost a lot more weather way before it held.
'I'hc wind continued light so, after tidying u p and waiting a few minutes, I sct the whole main sail and the jib and got under way again. At first, she held her own against the strong tide closc hauled but, just as I was beginning to think I would make the slack water on the Castle sidc, therc came a sudden squall and though I was holding both sheets ancl let them fly at once, the weather hull rose slolvly but relentlessly despite my full weight on the weather sidc deck until I \\-as dropped into the middle of the mainsail. 'I'here was no per- ceptible pause as the mast hit the water and the Slrear~oatcr turned right over without interruption till the mast touched bottom at some 12' and there I Ivas, swimming below what had been the weather hull with the tw-o hatch covers, a paddle and my tool box floating closc by.
My first thought was " Stay by the ship - she is your best lifeboat " - al~vays the best thing to clo. Then I started to consider how best to minimise the damage. I caught the paddle and bent on the ~ n d of thc main sheet. Then I cast off the jib sheets. 1 tried to reach the side stays to let go the mast but one sidc was too deep and the other was too high. Soon, ho\vevcr, we were carried into deeper water and I was able to reach the shackles. Fortunately, I had my shifting spanner on a lanyard so the shackles came adrift quite easily and the mast floated u p alongside. Nest, I let go the main halliard at thc peak and hauled down the sail from the tack. 'The sail and boom then came clear so I left them and let go the jib sheets at the clew and the jib halliard at the head.
About this time, I noticed a white motor boat coming downstream and assumed I would be taken in tow so I redoubled my efforts to clear the gear ready for towage. I was trying to untangle enough anchor warp to tow by and, when I looked up, the motor boat had passed on.
By this time, the tide had carried me downstream opposite Strood picr. A tug was corning up river quite slolvly so I stood up on the
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P I V E R 9 S T R I M A R A N S
Nugget
30 ft. X 18 ft. X 2 ft. N i m b l e Plans cost f35 Crossed the Atlantic in 1961 and proved thoroughly seaworthy in spite of continued gales. She has clocked 24 knots and can sleep six. The designer built this in six months working only evenings and week ends.
24 ft. X 14 ft. X 18 ins. Nugget Plans f 14 10s. Has, cruised over 1,500 miles from California t o Mexico w i th a crew of three. Maximum speed 20 knots. The floats can be made t o fold for towing.
20 ft. X I 2 ft. X I 5 ins. Banner ( t ra i lable) Plans f 9 Is specially designed for racing and day sailing, as is the smaller.
16 ft. X 8 ft. X I ft. Fro l ic Plans CS Several hundreds of which have already been built in the U.S.A.
28 ft. Encore L27. 32 ft. 6 ins. H e r a l d f5O. 40 ft. Victress 685. 45 ft. Meda l l i on L1 10.
Arthur Piver is the leading American designer of trimarans and his designs are only marketed after having been thoroughly tested. He always builds a prototype and proves their worth first. The simplified building system eliminates the need of all traditional boat building skills. They are quicker, cheaper, and easier t o build than any other type we know of. Virtually uncapsizable they are equipt w i th an automatic sheet release device. One of the most manoeuvre- able sailing craft afloat.
Quotations can be given for completed craft.
In U.K. plans available from :
The Shop, Soutergate, Kirkby-imFurness, Lancs.
In America from :
Pi-Craft, 344 Sacrament0 St., San Francisco II, Cal i fornia, U.S.A.