Formula 40 singlehanded trimaran build log

I believe that to be the case, StressForming + core (SF+), not CM. A 3 mm ply is folded up as one sees in the Gougeon book, or Kurt's manual. Then once you have that tidied up, you lube the surface with abundant glue, and press in balsa core. Then you vac bag that with a shopvac. Once that is down and cured, you bog any areas that might not support fabric, you pre-peg the fabric, and you spread it out inside the boat, and bag it down with the shopvac. The biggest hassle is pinholing in the fabric.

I have crawled through the tube, of Gecko, and it was all bagged fabric in there. And I think maybe the picks of a bagged core SF+ boat in the manual, are Kurt's 40. Certainly a similar boat.

Gecko has very low resistance hulls, so CM is not the only way to shape the hull. If you go through the ten or more hull types common in multis, most of the hulls can be SFd, and don't need CM. Some can't be CMd. CM has an additional advantage, in certain areas it is incredibly cheap to make. Also you have to sorta do an FE weight analysis to determine if balsa core will actually lighten your boat, or lighten it more than a negligible amount. When I did my boat, the ama decks would not have been lighter, so why spend the money. But cored decks and cockpit sole where very much worth the effort and cost in every way.

 

Yeah, but he obviously doesn't agree, I would have to see where those numbers come from, and for what quality of stuff, they are very low. Plus since he isn't taking your suggestions, your advice is only relevant to the wider community where similar decisions are under consideration, and it sure isn't representative where I live.

Are there a lot of KISS F 40s? The thing with Kiss is that after taking in a seminar, and building a mold you get "most of" your panel that is clean, is eaxctly my thought, the bit that goes in the water needs tape, etc... and it would all need to be faired all the way out over the panel, and polished, not really buying it.

That is one way of building in foam, not the way race winning boats are normally made, it is at best a second or third tier thing, like CM or somewhat worse. The way most foam is built, the way an alternative foam KHSD would be built, would not be a step ahead in fairing. That is just a fact.

I certainly think foam builders are entitled to believe what you say, but objectively no more than ply builders.

Well obviously not. The Gougeons ply boats regularly whip everything anyone has put out there. I think both OZ (?, little america's cup) and the French have the distinction of winning against them through the rule book. They beat boats in carbon and foam. Is a 35 foot race boat that can be cruised, with a real double (been in it, briefly for a look), that weighs 1K KG really so heavy? This class has a minimum weight limit apparently, so in the real world why spending for fancy materials just so we can add ballast.

Stiffness has several components, and is not just thickness, but I know what you mean, the third power thing. However, that is panel stiffness, there is also the global stiffness of the tube, not sure how that will be any worse. And Gecko was ply, balsa, biax or triax, so just crazy stiff, absolutely no concerns. I have been on quite a few boats like that, and they feel like walking on concrete. The governing loads are the walking loads, and you are walking on a sidewalk. The cycles to soft are way higher than in composite glass. Intelligent design starts with a well defined service, and then operating within the various budgets, weight in this case. Not sure where there is any problem where that is concerned. What I heard about Gecko was that she was flexie, so I would be looking at a carbon budget for the beams, or stays. Just hearsay, though.

 

The prices are based on WHAT I HAVE ACTUALlY PAID. I am building a catamaran in foam sandwich right now.

Materials used are diab divinycell m80, some airex c70.75 , and a little core cell. Fibers were from colan and metyx, epoxy was ATL s r246 system. It's much cheaper if you buy via the 200kg drum. It's all top quality stuff.

Sourcing materials is just as important as anything else in a boat build, effective searching and sourcing can save you as much as 50% in costs. I should write a book about it...

Corley already knows this stuff as he asked me about it a while back. I think he simply wished to stick to the plans rather than have to reengineer everything in a different material. This is merely just for the information of other interested parties.

Fairing is not required on a properly infused kiss panel. If you stuff it up, then sure you end up with pinholes to fill. The inside of my hull shown here has no bog whatsoever on it, paint straight on;



Before paint;

 

My observation so far is that to build to a similar relative quality the Cylinder molded option still has a price advantage in terms of raw materials and if you follow Kurt's budget recommendations the savings are there. It's not half the cost probably more like three quarters of the cost which is still quite significant on a 40 footer.

Cylinder molding is a fairly natural fit to an application like a skinny racing trimaran perhaps less naturally suited to really voluminous cruisers but experienced builders seem to still be able to create some impressive boats with pleasing hull shapes when using the method.

Kurt's stock plans are an absolute bargain too for what you get imo.

 

There's no reason one couldn't cm in foam either just sayin

 

I would agree, and you are doing very well at those prices, the thing is all that applies to wood also. I go from virtually zero for wood I harvest myself to deals on sheet goods that are 2.5 to seven times cheaper than what you quoted. Why would that be? You aren't wrong to want to build in foam, or KISS. But if you wanted to build in wood, why would you not apply your powerful mind to that problem also. Fundamentally wood is cheaper. That is unlikely to remain so for all that much longer, as far as ply and primary wood are concerned. It very nearly wasn't true, before the great carbon suck up of the 2nd gulf war/airbus, or whatever that was. But for now it is cheap as dirt. And the boats last a lifetime, so what is the downside.

panel is the operative word right? SO far you can't infuse a kiss boat in one piece and with no joints, though you can get long bits that are certainly longer than a piece of 4x8 ply.

What are the brown bits on the bottom, are those protective shoes?

 

The downsides of wood, is not the cost... I agree that timber is still cheaper, but here in oz, there's not much in it. This is largely due to the raw materials for the shell, isn't the majority of the cost in a sailboat. The rig, sails, deck hardware, electrics, engines, etc make up the vast majority of the total cost. Therefore, at the end of the project, you might have $150k in a foam boat, and about $135k in a ply boat. The 15k difference, will be made back the instant you sell it as foam core boats hold their value better. Not a big deal tho...

for me, the big deal is the weight difference. A high performance boat , must be light, period. The better the displacement length ratio, the faster it will sail.

Wood is also a bugger to deal with. If it's not looked after, the sheets warp and twist and it's difficult to make fair structures. Foam doesn't have any of these issues, it always lays flat, and I find it easier to get fair structures without resorting to heaps of fairing afterwards. This is a big deal for people like me who build outside, under temporary shelters and tarps. Not such an issue if you have a commercial style shed and can control the humidity and keep the weather out of everything.

You can infuse the whole foam boat hull in 1 shot, but it's not really kiss then. It simply becomes a molded boat using infusion processing, which is a brilliant way to go provided you have access to molds ... Not an economic option for a one off tho. Corley, do you know where the molds are for jessica rabbit , the Martin Fischer design? I love that boat, I'd seriously consider building one if I had access to those molds ...

The brown stuff on the bottom is simply black epoxy paint, I painted the bottoms with it before I turned the hull shoes over - as I didn't want to paint it with the hull bottoms so close the ground. I paint the underwater line in black so when the antifoul wears thin, is doesn't show a white coming through and starts to look crappy.

 

Unfortunately I've not seen a dry weight for Jessica Rabbit but just an eyeball of the boat suggests it will be a heavier boat than Kurt's 40er maximum sailing weight is 3.7 ton that infers considerably more skin area to obtain the displacement. Basic cruising amenity adds weight quickly even fairing the interior adds more than you might expect.

 

Yeah i read the same, 3.7t is the maximum designed displacement, including crew and gear, sails, supplies, everything... Something around 1 tonne less would be a ball park figure empty IMHO...33kts in 20 kts true wind is pretty impressive!

 

Gecko supposedly weighed in at just over 1790kg. I would love to see how you would build one in foam and fiberglass that comes out lighter. I don't see how it can be done without sacrificing strength(adequate stiffness and impact resistance).
Maybe in something exotic like nomex foam with prepreg carbon?
Example: The Extreme 40 catamaran comes in at 1250kg made with these materials. But this is a 26ft wide catamaran, not a square trimaran and is designed for coastal and inshore races.

 

Jessica

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According to Martin Fischer the Rabbit's maximum weight incl everything and crew is 3.7 tons. Post #2 here: http://www.boatdesign.net/forums/multihulls/jessica-rabbit-40-foil-equipped-trimaran-46495.html

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Groper, Martin Fischer is a member here -you can ask him directly about the molds.....

 

Hi Doug, I realize that but there was no lightship weight mentioned for Jessica Rabbit my guess is similar to Groper's that it's somewhere in the range of 2.5 to 2.7 tonne. It has a 30hp diesel which is pretty heavy by itself and a reasonable interior that can sleep 6 people. These features were probably part of the required brief and they probably make it a much more useable and practical boat but there is a cost in weight.

I had a chat with a friend of mine a while back who was interested in building the Rocket Factory 42 trimaran the cost of materials was over 90k. That was with a foam sandwich build with carbon beams and appendages and no float foils. So while fancy boats are nice the costs rapidly escalate with the weight. To my mind it reflects that the cruising amenity and nice equipment which is seen to be considered essential now adds up to making unnecessarily heavy boats if your focus is racing.

If your a poor slob (like me) and happy with an extremely basic boat the cost while still high in mostly non exotics is more achievable. It's also worth noting I haven't turned the screws on my potential suppliers yet to see what I can get them down to in ply price for bulk.

http://trimaranproject.blogspot.com.au/2013/12/tony-grainger-designed-rocket-25.html

 

I'm not familiar with the rocket factory 42... But a boat like Kurt's formula 40 is very minimalist . I doubt there's much material cost difference, whereas a larger tri like jessica rabbit , even tho it's still 40ft, would take a lot more material to build it. Therefore to change from ply to foam, would see a larger cost increase and but also a larger weight difference.

I concede, that a small volume boat like Kurt's, would only see a minimal difference in weight, I didn't realise how minimalist it really was... At least you can take comfort in knowing there's a lot less work to do in it!

All I needed to know is whether the molds were in Australia or somewhere overseas... If they're overseas, which I suspect they are, then it's an immediate non starter...

 

I should stop over thinking stuff but my thoughts on a minimal interior fitout go something like this.

I was thinking of putting a bunk under the cockpit sole (hotbunk for shorthanding) a very basic galley opposite the saloon seat and maybe a nav console in the area next to the daggerboard case. In preference to a normal companionway I thought perhaps to use an escape/reentry hatch which addresses some of the Cat1 issues and allows closure from the inside.

Internal headroom in the area adjacent to the companionway is about 1.4metres so It's pretty tight in there. I'm tempted to put a small blister or coachroof in the area for a bit more room and allow standing at the galley to cook the freeze dried food packets. If I can somehow afford a carbon rig it would give us a weight saving that would translate into useful extra payload a small fridge would be nice, time will tell. A bucket in a bracket with a lid for a head.

I have my Kraken 25 trimaran to finish first so I better get on with that and stop dreaming

 

Don't stop dreaming-its the food for the future and keeps you excited enough to deal with the current reality. At least that's what I tell myself.....