My crew tried to puncture my hull with her trapeze hook about 3 weeks ago. Resting on the hook with her 55 kg weight and for good measure she started by slamming into the deck and then compounded by slowly sliding of the hull dragging the hook with her. Result : over about 50 mm the paint has been scrapped of the hull and over about 100 mm you can see/feel a very shallow depression (the track made by the hook). The single layer of class is fine and only the force of the scrapping is revealed by the fact that some fibres are curved in the direction of the hook moving. No loose fibres or other damage, just some small repositioning. Epoxy coating is in tact, timber (4 mm thick in that area) is fully in tact, glass layer (only on the deck between the beams on my boat and a single layer of 150 grams). damaged area and the area around it are completely in tact without any secondairy damage. No delamination (hardly possible on my boat as I hardly have an glass on my hulls), no cracked zones, no buckling, no large dent, no what ever !

Actually the damage is purely cosmetic. A touch of paint will cover the area that was scrapped bare and then only a very small depression (the 100 mm track of about 5 mm wide) will bear witness of what happened. I can live with that.

In my opinion, if this happened to a foam sandwhich hull then I would have had a punctured outer shell and a glass repair job on my hands instead of a small "touching-up" paint job.

I'm now a full believer of marine ply as an excellent catamaran hull building material !

Wouter

Ply is a brilliant material for rigid low-weight construction - especially when combined with epoxy. My '84 trials boat was constructed from 4 and 5mm tortured ply reinforced with epoxy and locally reinforced with woven rovings and epoxy. It was stiff and fast and came in so light that we had to have 'heavy' centreplates made as we had run out of allowable maximum correctors!


The added beauty of a varnished boat is just a bonus

John, those old wooden T's are incredibly beautiful! And I agree with Wouter that wood is still an excellent material. Wood fibers are superior to glass when testing on repeated cyclic load. (The glass doesnt fail, but the matrix often do, I believe).
Wouter, I do think that plywood (if that is what you used) can delaminate..

I am wondering a bit tough, as the T was a plywood design. Are todays composite mass produced boats heavier than a ply design would be? Are they no stiffer than a ply boat (with comparable beams)? Are the glassfibre boats just a economical question?

Yes.


Wouter

I agree with you that a glass fibre foam sandwich hull would have faired much worse. Two anecdotes:

(1) On a light air day in between races I thought it would be really funny to push my crew in the water. As I helped them back out they tried to pull me in and dragged me across the deck. The hook of my harness punctured the glass/foam construction deck of our Tiger - duhh!

(2) A friend of ours tells a great tale about losing his footing on an I-20 and swinging in to the side of the hull such that his harness hook went right through the hull and left him stuck to the side of the boat as it began to heel over. Could have been rather serious! Again, glass/foam construction.

Ply/Epoxy or cedar strip construction rulz for robustness...

Chris.

"My crew tried to puncture my hull with her trapeze hook about 3 weeks ago. Resting on the hook with her 55 kg weight and for good measure she started by slamming into the deck and then compounded by slowly sliding of the hull dragging the hook with her "
Wouter, tell her she wasn`t trying hard enough - you know what my crew did to my hull (4mm ply, no cloth), lost her footing, slammed into the boat and hey looky, 25km from the beach, and a 200mm long tear in the hull. I think what made it puncture was that it was right next to a bulkhead, so the wood could not flex at all and just cracked. I also think she hit the boat side-on, and it was the stainless steel spreader bar, not the hook, that did it.
You`ll need to take your crew out again and practice that move if you want to put a hole in it .
Nicest thing about plywood is the DIY repair option, low tech repair, did it myself and I`m no handyman., and you can hardly see it.
Steve

Back to the question at hand : Why is the Tornado so fast ?
That`s easy - it`s because it`s really just a scaled-up Mosquito !

That is a beautifull T .

Locally here in MI is the Gougeon Brothers West System epoxy ,-there are excellent books and resources available from them as well as expoxy and related filler and boat building products .Wood is a wonderfull renewable engineering -building core material.
http://www.gougeon.com/

Became interested in cat sailing by reading Reg Whites books on the early days of C Class cat racing and what became known as the Little AM CUP ,-their preference was wood const .
wow --just searched a copy of his catamaran racing book for 3.95
http://www.alibris.com/search/searc...mp;qsort=r&cm_re=works*listing*title

Catsailors were building 150 LB A class cats from stressed skin ply and epoxy in the 80s locally and 18 sq meter class cats latter ,--the local builders/ sailors of them after numerous successfull A class designs went to foam and honeycomb core materials only due to the curve limitations 4 MM Marine plywood has ,--that is they wanted hull shapes that had flatter forward hull sections with sharper curves at the waterline than the ply material would allow though the positive aspect of ply was its inherant bending limitation forced a more uniform mathimatical curve as it folded up ,-it is almost impossible to fold up a slow hull shape due to this .

-It would be impossible to build an inter 20 type hull shape from ply for example with its pinched bow sections and very flat harder chined hull shape ,--but the Tornado type hull is ideal with deeper narrower hull and gradual math curves in hull shape .

--The Inter 20 weight is 390 LBs --the Tornado class weight is 376 ,-sounds like yours could have weighed 340 ,-the stressed skin ply version can weight much less or any 20 ft similar hull design can weigh much much less nowdays due to much lighter componants also being available --lighter hardware --sheets lines sail materials mast rigging boats rudder assemblies etc --
believe a 20 w ply const. could weight under 300 all up -possible 250 w spin and all .

Hope that helps inspire some to build .
thanks again for the pic
best regards
Carl Roberts

Carl, and Rolf, thank you for the compliment. (about my old T)

It's so long ago now that I can't remember the exact weights involved, but I think the max correctors figure was something like 5Kg and we needed about 8Kg so because the boats were weighed with all gear on board we had a pair of centreplates specially made with LOADS of reinforcing that came out so heavy that when fitted we were able to put only 4.5Kg of correctors on the main beam

One other thing I would agree with - my boat COULD HAVE BEEN BUILT LIGHTER even back in the early '80's! So with modern techniques, knowledge etc. it should be easily possible to get a 20ft cat under 300lbs if built in ply.

As with everything the trick is to make it hold together

After building and using a wood composite boat, I agree it is superior to glass in many ways. The main advantage of polyester glass over wood, is that it is cheaper. Wood epoxy is a lot more like carbon epoxy than glass polyester.

I pulled a similar trapeze hook stunt a couple of weeks ago. I meant to jump off and miss the boat. Instead the hook caught the deck. Result scrapped paint and no damage to the hull. This was a prepreg carbon Marstrom A.

I suspect, that you could build a monocoque wood/epoxy boat that would match carbon by cold/vacuum molding wood veneer over a plug. By investing in a bag type plug** and using carbon and kevlar reinforcement it could be a case of prepreg carbon trying to match you.



**Bag type plug - 1 version is a silicone rubber bag filled with .5mm steel spheres. The bag is molded to the shape you want and then a vacuum is pulled on the inside of the bag. The bag becomes very rigid. During molding the bags sticks out through what will become the access port. When you are finished, release the vacuum, pour out the spheres, and then pull out the bag leaving only the mystery of "how did they do that".

Well actually the biggest drawback of wood (marine timer) construction is the labour involved in folding up a set of hulls. It also requires a higher skilled workforce. As today labour is a very expensive cost component glass-vinylester wins in the economical sense when trying to make a living off it. Sadly marine ply + epoxy wins in the engineering department. So we are all faced with a choice.

That is unless we can get some cheap skilled labour force in some asian country and have the timber epoxy hulls produced there with a single (light) layer of glass to enhance impact resistance some more. THAT would be the ultimate hull. Thanks to Phills efforts we can make a little bit more complex shapes with folded ply.

Wouter

Hi Wout
Thought it may be helpfull to provide a link to Phil,s excellent boat const. oriented web site
http://www.geocities.com/phillbrander/

different related topic
--good effort on the rating system concepts and proposal,--it seems they all --all types of rating systems and design class rules ,inc Formula Class are all continually works in progress ,--constantly developing and refining over time and changes ,though much the same in intent through yacht racing history .-

Hope boat mfg will eventually get behind a Formula 20 category cat with common accepted basic specifications to go with the F-14 -F-16 F-18 ---f-20? concept in some form , perhaps based on the Tornado specs, which were the original B Class as defined ,-the T developed for selection trials in the B Class as Olympic class catamaran way back .
C

If you wanted to build a T out of wood epoxy, where do you find plans? The official T website shows a deleted link to plans, but no more. Google turned up nada.

Jimbo

I think the real reason a Tornado is SOMETIMES faster than most of the production 20's is the 10 foot beam. You can keep it powered up into a higher wind range than a boat that is only 8'6" wide. I don't know what the Olympic class weight for the T is but I would guess it's under the typical Inter 20 wt. of around 420#.

But, I think if you were to build up a custom I20 with 10' carbon beams, carbon boards and blades, lighten up what ever else you could to get it near the Tornado wt., it would be as fast or faster. The I 20 has very fat forward sections and a tall bow, you can really press it downwind very hard before you stuff it.

Jimbo,

There are Tornado plans at thebeachcats.com site. The text there claims that they are the Houlton building plans, but a few days ago I showed them to a guy that I work with that worked in Houlton's shop in the late 70's-early 80's timeframe and his recollection was that the plans shown were for an older Tornado design that Houlton worked from. Apparently he (Houlton) engineered a trusswork internal structure that was remarkably strong and lightweight to replace the more conventional ply bulkhead/stringer framework. My co-worker remembered lots and lots and lots of little gussets.

I'd love to see those plans. Although, considering the itch I have to build a boat, maybe it's better that I don't.

I was just over at the TornadoCat Yahoo group, and there are some pics of the Gougeon brothers hull structure. No bulkheads. Trusswork with diagonalized longitudinals. Sweet.

The set of plans that I built my T from were purchased direct from ITA. From memory, I believe one set of plans entitles the purchaser to build 5 boats, although royalties need to be paid on each boat built.

Our boat was built in a similar way to the Gougeon boat shown, with lots of thin bracing and trusswork. The plans don't show this but it is relatively easy to work out for yourself (to replace the re-inforcing shown).

Our main problem was getting access to the official IYRU (ISAF) measurement templates so that we could check shapes as we progressed. Fortunately a friend knew someone who had a set that they had made up themselves in ply rather than the aluminium of the official templates and they were good enough!

If I were 30 years younger, I'd do it all again

The plans and building tips on theBeachcats.com was collected and distributed by Jerry Houlton.
I have learnt later that Jerry bought the moulds for the Gougeons Bros. cold moulded T's, and your friend is probably thinking about the building of those.

If one builds a Tornado, they have to pay the ITA a building fee when measureing it. It will not be allowed to race or measured before the building fee is paid. The ITA pays Rodney royalties for every boat measured I believe (at least they did earlier, but I heard something about re-negotiation the deal with him).

The templates can be bought from ISAF, in mylar these days I think? They also supply the original plans, but I think Jerrys notes are superior.

If anybody is interested in building a T in plywood, they should join the T-cat list at Yahoo, as there are several possible modifications to the internal structure shown in Jerrys notes.

John: Was the wooden T on the picture earlier homebuildt? If so, whow!

Rolf, Yes (with the considerable help of a cabinet maker) and Thank You!

Many moons ago I help someone unload a Wooden T at Rutland before a cat open there. The boat was fantastic. The Black 911 Turbo he towed it behind was not too bad either !