Tornado Boat 2

8/6/2019 Tornado Boat 2

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t hc J 1 \\" I -'. t hroughout, though a short piece of right angled V"at how

and stern \\" iJI clamp S(HIle pitch ing. " lh is hu ll w ill manoeuvre easily,

have t h e m in imum w etted su rfac e and w il! \\"cigh le ss . If it doc s

pitch in light winds, the drag aft wi]] also he l ess but this is a sll14111

consi d crat ion compared with the loss of sail drive in pitch ing .

•Sai! Dccclopmcnt, '1'0 date, the Farrar wingsail has clearly

ShO\\"Il its superiority to the previous \vingsails and, of course, to the

sloop. 1ts only r ea l c omp e ti to r at th e IIIOIl1ent is th e p oc ke t luff ic c

yacht rig with a mast bcndy enough to untwist the sail. .:\ final

iII P rO\"CITlCIl t mi gh t, 11ow cvcr , l ies in a sem i -c ll ipt i ca l sai I set, either

as a squaresail of "fore-dipping" lugsail. 'This cannot be known until

it is tried.

the rcsul t of

the shape up.

'I'hc evidence

Ccntreboards. ' l'hc boards at present used arc

acrodvnamic theory with few or no tank tests to back- _"

·I'hev are high aspect ratio more or less vertical boards.

frorn th e tank , however, indicates i-

(1) That the leading edge should be sloped aft at about 65° from the

vertical. (Southampton 'r ests).

(2) ,I'hat the aspect ratio should 1: 1 ( Edmond Bruce).

(3) 'rile boards should be large (Bruce).'Ihere is no evidence on the shape of the leading edge of the board

but it seems reasonable to have this slightly convex with a small

c()nGt\'~ "fairing" where it joins the hul l (Srni th: H\Vhy Sailboats Win

and J .osc Races"). ~or is there much evidence as to whether or no

IHJards shc)u l d be thin or stn ..u ru li n cd shaped.

Conclusion, On the evidence, tile boards should be triangles,

more Of less, being twice as long at the hull as ill draught. This at

least is a traditional shape as fuund in the American sailing fishing

boats which had no real thickness. Catamarans with the dinghy- type

revolving boards could try this shape at little trouble. Those with

dagger boards could try it by attaching it to the bottom of their dagger

section and putting i into the slot from below.

I t is perhaps noteworthy that the shape suggested here is found

in the fins of fish.

U ' J . V1 O RA T

by Courtesy of the Editor, "Yachts and Yachting"

i.;.« 1s ft. 0 in .; b ea m 7 ft. 6 itt.; H/eight 120 Ibs.

Three years ago, cat designer John Mazzotti carne up with a new

method of hull construction. By using developed pI y panels for

e ith er s id e of the hull and h old in g th em together at the keel at a pre-

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John Masixott] uses a t r(/l)c~e 10 driuo l T!V I( 'C)I~ \T Oil (/ close reach .

A s li d/ lI g s ca t 1//(1), he jilted i] preferred,



dctcrrnincd angle with fibreglass tape, he found that he was able to fold

t lie panels in towards each other to fonn a very good shape for a

catamaran hull. Early experiments provided the ground-\vork for

:\Iazzotti's successful "B" Class I\Ianta design.

J oiln ~ Iazzotti has been foldi ng pIywood again and his latest design

lS the vcry easy' to bu ild and extremely quick lJiVJC'()/~N "A" Class

cat. Once again the designer has produced a boat which is ideal for

~1Ina t .cu r const ruction. 'Ihe building proccd urc is simpl ici ty itsel f and

no jig is required to produce the right hull shape.

L!~\'J('Ol?l\T is 10ft. overall and 7 ft. 6 in. maximum beam.

These arc the maximum length and beam dimensions allowed by the

"A" Class rules. The boat carries 150 sq. ft. of sail in a simple una

rig and this, coupled with the extremely low all-up weight of about

] 50 lb. ensures a very high turn of speed.

The "A." Class singlchanders are allowed to usc either a trapeze

or a sliding scat as a sitting out aid and UN!C'()/<JV can be fitted with

either. 'rile designer himself prefers to usc the trapeze because it is

so simple and because a sliding scat increases the all-up weight by

] 0 pounds or so.

At first glance, an ".A" Class cat Blight seen) to be something of a

problem to manhandle ashore. However, not only is Ui \TICOl?N

extremely light but she can be knocked down into her main components

of hulls, cross beams and spars very quickly indeed once she has been

brought ashore. 'Trailing is no problem and the boat is as easy and

quick to assemble as it is to take to pieces.

' I'hc or ig inal method of stressed skin hull construction makes for

gr<.:at strength because localised stresses cannot build up but arc

dissipated throughout the skin. Only t\VO bulkheads arc used in the

construction and these arc glass taped into the hulls after they have

been folded to shape. One is positioned just ahead of the main beam

which is made from a length of standard mast section tubing and

ca rries the mast. The other is fitted in way of the after beam whichca rries the mainsheet track.

Limber holes are provided in each bulkhead at the keel line so that

any water finding its \vay into either hull is easily run out through the

drain hole in the transom. No reserve foam buoyancy is needed

because, in till: event of a hull being holed below the waterline , sullicicnt

wa te r will f]O\V into the hull to flood the compartments between the

bulkheads above the level of the limber holes. Water will continue to

f]O\\' into the damaged hull only against increasing air pressure and a

balance will be reached while the hull still has plenty of buoyancy.

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•

UNICORN's una rig carries a typ ica l catamaran sheet ing arrangement,

A full width horse is f itted to the aft beam uihilst a curved track is used

for the kicking strap.

On hauling the boat ashore, the transom bung is removed and all

the water is run out.

The materials list for L T J \ T ICOl?).\T is short and the bout's per-

fonnancc docs not depend on a number of expensive fittings. After

buying his spars and sail and having built his boat from scratch, a

home builder can be on the water for as Iitt le as [150. To date six

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.11 una rig of 150 sy. ft. is se t OJl a rotating IIUISt supported by one pair of

sh rou ds a nd a d iu id cd [orestay,

boats arc racing in the class-s-four of these are hOIIlC built~and the

L ] 50 figure has pr()v~d to he a \'ery reasonable average cost.

At the moment LjiVl[I()J~j_V hulls are of all plywood const ruction ,

but'"work is in hand for a fi hreglass hulled prototype. 'This should be

all interesting experiment, for t he i nt en ti on is to build a UNICOJ~lV

wi th on c pI vwond all J 01lc Ii brLglass hull. 'rile boat wi ll then be

tested to see which is the first to fail.

(/ jVIC:Ol~NI-S arc built professionally by 'Trowbridge and Sons of

l)urnchurch\Vinchester and the cost for a boat complete with sail is

£300. Kits 'are available, of course, and either a complete basic set of

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UNICOl?N's hulls are held apart by t zoo beams, the centre area being

filled with a Terylene trampoline supported down the middle b), all

aluminium tube. Access to the bolts which secure the beams to the hulls

i s obtained through inspection hatches ill the deck.

•

LAYING OUT PLY FOR HULL

USE THIS PIECE

FOR FOREDECK

SCARF CUT OUT ONE PAN EL TO

USE AS TEMPLATE FOR

THREE PANELS REMAINING

parts can be supplied or the boat can be ordered in any stage of com-

pletion. For the cat sailor who is good with his hands and wants to

start from scratch, a complete set of working drawings and buildingins tructions can be purchased from the designer fo r £8 Os. Od .

CONSTRUCTION

The first job is to scarf together plywood sheets to form t\VO

panels 18 ft. 2 in. long x 4 ft. wide. One panel is sufficient for each

hull. The width of the scarf should be eight times that of the thickness

of the plywood, in this case 32 nun. or about 1* in. Pressure can be

applied to the scarf while gluing by nailing through a strip of packing,

through the panel being scarfed and into a wood backing batten.

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\ Vhcn the glue has set, the nailed stri p can be removed and the holes

stopped up when painting. ~rhc sketch on the r ight ~ho\vs , the Inctl~od

of "st itching" the panels together with copper wire prior to hbreglass lng

the keel joint.

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After the hull sides are cleaned up to shape the gun\\ 'hale assembly

can be fitted. The lin. square spruce gUI1\\·hales arc fixed to the

upper edge of each panel OIl the inner face and fastened w ith g lu e and

barbed ring nails. It is important to Blake sure that two pairs of right

sides and two pairs of left sides arc assembled. \Vhen the glue has set,

each sheet should be marked and cut out where the main beam and

rear beam mounting blocks are to be fitted. The blocks and their

doubling pieces arc then fastened into place. ~ ext, the deck beam

chocks are fitted. These are nailed and glued to the panel just below

the gun\vhale.

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IJ~·fl.lt ....(. I~·~·-.~

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WIRING HULL PANELS

DRILL 3/32" DIA. HOLES AT

4" PITCH

-- - - - - -

~CHAMFER

EDGE OF

PANELS

INSIDE

PLY HUL L

(1) JI arhiug out

.:\ datum line is marked on one panel and the offsets for the keeland deck 1inc are marked ofT and the outline of the finished panel

drawn in. One panel is cut out and carefully finished to shape. This

is used as a template to mark out the other panels. Care must be

taken to ensure that the face veneer of the plywood appears on the

outside of the panel and that the scarf is trail ing. That is with the join

starting on the inside of the [inishcd panel, forward and running to the

outer fa ce of the panel aft. A] ()~ i n. wide offcut of plywood between

the hull panels aft is used for the foredeck.

COP?ER WIRE

MAKE CERTA IN THAT

GUNWALES FACE INWARDS

(3) W iring to geth er

When the glue holding the gunwhales and chocks has set, the

gunwhalesrmust be tapered for the forward lOin. off to nothing at thecO ,

bow, As ~his will expose the ends of a number of the fastenings, thesewill have to be punched back and removed to avoid blunting the plane

or chisel, The sides are then paired off and marked so that they

cannot be mixed later. Each pair is placed back to back and a row of

holes, 3/32 in. in diameter, is drilled along the keel and up the stern.

The holes should be about 3/16 in. from the edge of the plywood and

spaced at about 4 in. centres. The sides are then reversed so that the

gunwales are inwards and wired together using 3 in. lengths of 16 g.

copper WIre.

DECK BEAM CHOCKS

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SC,t..RFS--~~

CHOCKS FOR MAIN AND

AFTER BEAM

GUNWALES A _ r : - l _ Q _ ~ E A ! v 1 CHOCKS

TAKE CARE THAT

GUNWALE AND BEAM

CHOCKS ARE FITTED

TO THE CORRECT SIDE OF EACH PANEL

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GLASSWORK AT CENTRELINE- ---- ----- ..._ - _ " _ -- . . . . .-

sharp corner where the panels meet is rounded oyer with a plane and

t\VO layers of glass tape arc bonded over the outside of the join. \ Vhen

the resin has set hard the panels are ready for pulling to shape by fitting

them into a jig specially made to dimensions shown on the drawings,

or by driving a series of nails into the gllIl\valcs and pulling thc sides

together with line. 'L'he bulkheads, centrcboard cases and deck

beams can now be fitted.

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;, ~ ),() P Ph f'J E L S APART

r r ~ A T THE '( ~ A A V EAr ~

/··;(;LE OF 1)(/)

2. t~ : [h TH PPOP GLASS TAPE

COMPLETED HULL

CHOPPED

STRAND MATHATCH

( 4 - ) Classicork at Keel

\Yhen the sides have been wired together they are spread apart

l ike opening a book to an an g le of about 120~ and held in ?lace by, a

single shore fitted between the gun\\'ales about 2 ft. aft of , the mam

bearn position. :\ template of plywood .is cut ,to 1:OoanJ \ \' I,red to the

sides at the stern to maintain the angle nght aft. Epoxy resin such as

..Araldite is recommended for use wi th the fibreglass for bonding the

keel. A strip of 2 in. wide fibn:glass tape is bonded to the joint offset

.1 , in. one wa y, followed by a 1 ~ in. wide st ri p of chopped strand, mat

clown the middle and finallv another strip of tape offset the other \ \·ay .

T w « 1 lb. mixes of resin ~ hou ld be su f licicu t for e ac h h ull.

MAKE SURE THAT 80TH

HULLS ARE CORRECTLY

ALIGNED WHEN FITTING

CROSS BEAMS

(6) C011lpleting Ilull

Once the deck framework and bulkheads arc in place the insid- of

~},lehull should be painted out with three coats of polyurethane paint.

1 he decks arc then marked and painted before being glued and nailed

in place. llales arc cut in the deck just aft of each beam to take an

inspection hatch and a ply doubler about ~ in. wide should be fitted

round the opening on the inside to take the fastening screws, ~ in. x

~.in. rubbing strips are fitted to the deck either side of each hull to take

the chafe from the sliding seat and the hulls are ready for final sanding

and painting. Finally, the hulls must be lined up carefully to eliminate

twist and the cross beams fitted.

DO no r WORK HULL INTO JIG

'JrlTIL GLASSWORK HAS HAD

TltvlE TO CURE

MAKE FROM 1/8" THICK

HARDBOARD EDGED

WITH 3/4"X3/4,f DEAL

''-" BATTEN TIES

"",

CURVE ~ DECK EDGE

"TAKEN FROM OFFSETS

GIVEN WITH BUILDING INSTRUCTIONS

(5 ) D eck Jig

Once the inside of the hull has been bonded along the keel and the

epoxy resin has set the hull is turned over and the wire stitches are

elippcd off close to the surface of the panels and filed flush. The

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AUSTRALIS AND rrOH.NAI)O NO\·V INTERNATIONAL

CL,ASSES.

I.\~.H..U. CA 1- 'Al \ I IAH.f \NS 'fl{If\LS .vr Sl-IEPPEY, 1967

It may be placed on record here that the I{.Y.f\., as an organisa-

tion, has never been auti-rnultihull but has followed the development

of the racing multihull with interest and quite early set up a "Cata-

maran Committee", 'The I.Y.l{.lJ. has follo\\'cd and last year decided

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to select both an "A" Class and" B" Class catamaran for International

status through a series of races at the Catamaran Yacht Cluh, Sheppey.

.· 1 [T.~~frN.·It.t» .m d '!'()N.\.·II)() we- r e selected.

Boat Designer Helmsman Po in t s

Tornado IT (U. J(.) Rodney March 'r. J(. Pearce ()1.0

Centennial (Canada) J 'crry I (~~ltcr G. S. Percy 104.0.

}/(dlrno /Jird (lJ.I(.)

( /) ~hear 'l oa t er I I I ) Prout F'. Prout 113.7. \" C \" R r: 'UJT'I.:~~ '.~ ~~

~\!ame Designer Helmsman [Joints

-lustralis (Australia] Johnston G. E. Johnston 20.7

11aI/I h i (lJ.IZ.) Prou t Coster N. 1'. Coster 25.4

Catalina (Denmark) Smitt 1.10Wagner-Smitt 34.0

Unicorn (U.K.) ~[azzotti J. Mazzotti 35.1

Sail }'ast ( U. I {. ) Hubbard R. J. Osborn49.4

Jliss Rothmans (N ./:.) Stanton Cooke

Bros. G. B. Stanton 49.7

Lo-Ka (U.S.A.) J(archer R. F. Lostrom 68.4 ,

Iolanthe II (IT .K.) Butcher P. Butcher 78.7

.- 1 [.l .STR_-lLT,._) won J races whi l e BAMBI, CATAL,I1VA, UNI-

COI<l\T and S & 4 . I I ~ }'£4k)]' won a race each, so the boats can he said to he

fairly evenly matched . . . 1 I T 6 . ') . . ) ROTlllvlANI.) dug her fore beam in

\V3VeS and threw spray. [,()-K... was fibreglass and therefore probably

heavy..

Design-wise, the boats were very similar in shape. All had fine

bows which experience shows go through waves without stopping so

much. ...4U.._C;;TRALI.S, howeve r , had a sharp ste rn w hich d id not seemto slow her at all. " .A_" Class cats pitch much more than larger cata-

marans and thi s fine ste rn might, under these c ircumstances, have Il)ore

than made up for the extra (strong wind] resistance, while the lesser

wetted surface helped in light winds,

TORN A no and 1~4H II1 7'A [ lE I" had this series more or less

between them. The older, heamier and heavie r boa ts were out -classed.

One could guess that the points obtained were almost in proport ion to

the weight s of the boat s concerned.

111EIIITABEI.I is a more or less typical Cummingham (QljEST)type but sports a small transom about 3 in. in width, She is tremen-

dously light with semicircular sections based upon the I.I.\V·.L.

throughout, as compared with the sharper sections of the other boats

forward.

Postscript, We have most certainly made some progress in

ca tamaran design since 1955 but the , ,) III~A R rv A 7'EI? / V st ill a c-

quitted herself wel l against the latest, longer, larger and leaner boats

and, after all, the 7~()I?NAI)() is not very different in design from the

dear old 6. )IIEARTV ATER.

'r()I?N A I)()

A n Class catamaran for international racing designed by HOD~EYIVTAHCII

by courtesy of the Editor, Yachting World

20.0 ft. Ream 10.0 ft. Sail Area 23 5 sq. ft.

"B' CLASS RESULTS

Boat Designer Helmsman Points

T orna do I (U.K.) Rodney March R. \Vhite 8. 7

illelzitabel (Austral ia) Cunningham

Blaxland P. Blaxland 25.7

Tlzai -Foon (U. K.) VlacAlpine-

Downie K. L. Sanger 69.1

Vi'l'ace (U .K.) Mazzetti A. G. J. Smith 70.7

}T a nk ee B (B - IJ io n)

l: .S..A, Hubbard l\'Iark Smith 70.7

ROt011 Pointer (U.8.1\.) G. \V. Patterson J. Bonney H2.4

Ready Steady Gone

(U.K.) Prout R. G. Prout X3.1

Pacific Cat (IT .S.A.) Newport Boats R. Baker XS.7

2+ ·

TORNADO was designed with the requirements of the Inter-

national Yacht Racing Union for a n Class catamaran well in mind,

and to such good purpose that, following the trials at Sheppey in

August, she is the hoat that will he recommended to the I.Y.R. U. at its

Novemher meeting hy the Ohservation Committee as a one-design

class suitable for international racing. Rodney March set out to

design a hoat which would have an exceptional performance. This

characteristic would necessarily stem partly from a light boat which in

turn would make her easy to handle ashore. The third important

factor i s that 7'ORNlll)0 is especia lly suitahle for amateur const ruc-

tion, using the "bent ply" method of forming the hulls.

'fOl?NJ1I)O's construction is the same as the bent pl y method

employed for 7t

IIlJN[)ER IT , which was a development of John

Mazzetti's 111AN7' . t 1 construction. By pre-setting the keel angle

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and into the after beam, which is a mast section complCle wun lUl

groove.

TORNADO promises to be a very popular boa t; she is undouht-

edly very excit ing and for the f irst t ime hrings in the added requirement

of downwind tacking even in lighter winds, hitherto a waste of time

with boats of her s ize except in special conditions.

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===--==~

Successful prototype TORNADO, international catamaran of thefuture.'--,~ -,---- -----

/when ini tial ly sewing and taping the keel together it is easily possible <

to maintain accurately a definite hull shape which can be repeated

exac tly. Three bulkheads and a piece of pre-shaped polystyrene foam

for the forward s tations assure perfect conformity to hull l ines.

This method of construction lends itself well for amateur con-

struction as only the minimum of jigging is required to hold the t\VO

4.5 mm. ply halves of each hull at the correct angle while the epoxy

bonded glass tape sets. . .Afur ther s imple j ig ismade to give the correct

deck level plan. This jig can simply be made from hardboard with a

piece of ~ in. square screwed around the hole pre-cut to accep t the hull.

The result is a hull with very soft lines which, in sp ite of the thin

skin , is strong, rig id and very light.

The now familiar configuration of aluminium beams and Terylene

"trampoline" are used to tie the t\VOhulls together and plug the hole

be tween hulls. Four stain less stee l straps on each hull hold down the

beams which correctly align the hulls on assembly. The bolt ropes

of the trampoline fit into aluminium extrusions screwed to the hulls

•

Production boats from Sailcraft., Briglttlingsea, Essex, cost £495, ex sails.

Kit £33R including sails.

2726 .

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26

and into the after beam, which is a mast section complete with lutt

groove .

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TORNADO promises to be a very popular boat; she is undoubt-

edly very exciting and for the first time brings in the added requirement

of downwind tacking even in lighter winds, hitherto a waste of time

with boats of her size except in special conditions."

'. "

•

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Successful prototype TORNADO, international catamaranof the future. '.".-l-_

;~

when initially sewing and taping the keel together it is easily possible ~-

to maintain accurately a definite hull shape which can be repeated

exactly. Three bulkheads and a piece of pre-shaped polystyrene foam

for the forward stations assure perfect conformity' to hullli~es.:~. .. ~ I ..

This method of construction lends itself well for-amateur' con-

struction as only the minimum of jigging is required tb hold the two

4.5mm. ply halves of each hullat the .correct angle whiletheepoxy

bonded glass tape sets. A furthersimple jig is made to give the correct

deck level plan. This jig can simply bemade from hardboard with a

piece of ~ in. square screwed aroundthe hole pre-cut to accept the hul l.' . -" ' ~~

The result is a hull with very soft lines which, in spite of the thin

skin, is strong, rigid and very light.

The now famili ar configuration of aluminium beams and Terylene

"trampoline" are used to tie the two hulls together and plug the hole

between hul ls. Four stainless steel straps' o n each hull hold down the

beams which correctly align the hulls on assembly. "I'he bolt ropes

of the trampoline fit into aluminium extrusions screwed to the hulls

\

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I

Production boats from Sailcraft, Brightlingsea, Essex, cost £495, ex sails.

Kit £338 including sails.

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Documents

Tornado Boat 2