Formula 40 singlehanded trimaran build log

Discussion in 'Multihulls' started by Corley, Aug 24, 2011.

  1. Corley
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    Corley epoxy coated

    The mold will be biaxial I'm going to have quite a few helpers around while bagging up the panels after chatting with a few builders using the method it strikes me that the more hands available the better. I'm also going to use a thixotropic resin to try and take up any gaps and voids in the bagged panels.
     
  2. Marmoset
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    Marmoset Senior Member

    Think I remember reading somewhere some cat builders doing cylinder mold build, and yeah , scarf joints were not bending as well as rest of panel causing voids and such. It might waste some material here and there but I would think strategic scarf placement could go a long way.


    Barry
     
  3. Auntie Frannies
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    Auntie Frannies Junior Member

    What type of ply did Kurt design for or specify?
     
  4. waikikin
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    waikikin Senior Member

    Hi Charly,
    I watched the KH cylinder mold video about 20 years ago, looked like a pretty wild day out but obviously works, do you do a dry run for fit up & order of the sheets? or they're just a standard square shape, is the problem area at the intersection of the longtitudinal scarf & scarf to next sheet or caused by the "biaxial" nature of the longtitudinal "camber"?

    Regards from Jeff.

    PS: anyone heard as to how "CB" is going with his KH cat? I know he's been back under some other handles but seems to have evapourated.;)
     
  5. groper
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    groper Senior Member

    He gone silent online Jeff, lost the plot, took down his website, got all paranoid about putting photos of his boat online and generally sounds like he went off the rails... of course he blames his psychotic missus for everything but I reckon that was other personality disorder speaking :D
     
  6. Corley
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    Corley epoxy coated

    If I recall correctly Kurt specifies a minimum psi rating for the plywood. Most Asian hardwoods would be ok.
     
  7. waikikin
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    waikikin Senior Member

    Pretty sure he's been back here under a couple of new names like ocean basher or some such.......
     
  8. Charlyipad
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    Charlyipad Senior Member

    I did the longitudinal scarfs beforehand, so the only scarfs that had to mate up when bagged down on the mold were the vertical joins at the panels. my panels were about 8x7 ft. For a 36 ft long cat hull. the problem areas were where you have the most bend in two different directions, ie the turn of the bilges at the spots where the hull shape turns inwards toward the centerline..in my case about six feet or so from each end.

    problem with a dry run is that the panel edges are fragile at the scarfs and every time you move them around you wind up buggering something up. Unless you have a very large workspace that is out of the wind it is very difficult to keep track of your layout and move the panels around without harm. you also risk puncturing the bag which was Catbuilders downfall.

    Kurt specs 6566, but I used 1088 okoume- too stiff.
     
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  9. ThomD
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    ThomD Senior Member

    How much shaping are you guys getting in your biax molds? Kurt built his 40 without any molds, it was SF. I found the flat mold easy peasy to do with two people. While I believe in CM, I am not all that clear on how much shaping it does. When my panel was cut out, the curve was basically only made in the deapest section of the boat, it gets trimmed away, if you know what a flat panel looks like. The molded piece is very impressively curved, just doesn't make it into the boat. Hull would have come out a lot the same had it been SFd. Now on a skinny race boat, what is the upside, it's narrow anyway. Same thing, with amas, proa float, podcats, race tri main hulls, only fat cruising boats are really all that beamy.
     
  10. ThomD
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    ThomD Senior Member

    Old is not the same as new. And a boat that covers nearly 40x40 and supports a rig way the heck up there isn't a boat which there isn't much to.

    The balsa I used was contour cut and had a removable scrim on one side. Basically you end up with a duracore boat, but without flat panels, or strip in the construction. You end up with a laminate that is 3/4" thick, stiffer than 3/4" ply, but weighs about what 3/8" ply weighs.
     
  11. ThomD
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    ThomD Senior Member

    Does the 40 use 6 foot wide pieces, or just plain sheets of ply? When I was on Gekko, it was like a stretched version of the 24 or 26, but with Kurt if he thought it needed an extra 3 inches, he would have you scarf it on the 20 panels, no corner cutting.
     
  12. Auntie Frannies
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    Auntie Frannies Junior Member

    So, you are saying Gecko was built with a standard tortured ply method and not CM?
     
  13. Corley
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    Corley epoxy coated

    The 40 uses the big boat mold so you use the scaphed (wide sheets) on the mold. I think ThomD is alluding to the fact that Gecko was originally built on a flat cylinder mold form rather than a biaxial cylinder mold. It would be quite possible to do that as the fineness ratio is so high on the hull but the biaxial mold takes a bit of the fight out of wiring up the flat panels into a hull.
     
  14. ThomD
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    ThomD Senior Member

    I think it varies hugely by region. At some point one ought to be able to Alibaba cheap composites for project sized jobs, so you could buy a balance of epoxy glass, carbon, and foam from China, particularly in OZ.

    But... Corecell is made locally, cost for that thickness is 210 dollars retail, 180 for 20 plus. Cost of the gallon or so epoxy for a 4x8 sheet 60-120 dollars for the good stuff. And glass is about 30-60 depending on volume. So you can easily go between 300 and 400 dollars a sheet. That is from a local distributor who has an NA wide business, there are a lot more expensive places to buy. If you commit to a boatworth of material you can lower costs, but there is a floor on what you can do without compromising quality.

    Back at the weight table you are looking at about 10 pounds of epoxy, and 8 pounds of glass, plus foam per 4x8. You are looking at 30 pounds plus for the plywood, so there is a loss there. I am surprised that it takes 3 layers though. The gougeons boats use 7mm total, though they do use a lot of little pieces as ribs. Anyway, there is probably no more than 30 sheets of ply in the main hull, I am not sure 300 pounds is all that big a deal, on a 40 foot boat, what remains is the 4 oz veiling on the outside. Often the main hulls have no real additional structure to support a CM hull, mine had zero, you need floors, bulkheads to separate off sections, etc... Amas do require a lot of bulkheads, but only if you SF them, that usually works out lighter than foam.

    I would imagine Kurt paid 7 bucks a sheet for his ply, so you are into your pocket for 210 (for CM), or exactly one sheet of corecell. Haven't seen that ply in years, not the cost, but the glue. So you can call it 40 for the rated stuff around here, for 30 sheats, you are looking at 1200, not too bad you can get 6 sheets of corecell for that. You use a ton less epoxy and glass.

    The real savings are time. You can make the main hull in 20 hours, sorta. You need an easy afternoon to make the deck jig, and prep all the materials. Then you need about 5 2 hour evenings to crack out the boat through to the point where it would be ready to turn and glass. To do that you need some special assembly techniques that cram steps together, but it works fine, and I am assuming no longy joints, which there seem to be for this hull. That is with bagging, you are probably looking at an extra day or two to do the CM, depending on how many stringers you need to cut out (some of the structure you need in any boat so it is going to be part of the post flip and glass on a foam boat), whether there are bulkheads that need bagging or scarphing.

    But the point is it is really fast to make the hulls. You get what you pay for in time, but who really has 10K hours to make a boat. I think to say people hang onto their boats (actively use) for more than an average 5 years, would be generous. Do you really want to spend 2K hours a years of ownership? Ad that time doesn't even assume the thing is floating. A lot of boats are sold before they are even used.

    So I am with Corley, don't spend more than you would loose in depreciation, and spend as little time building (plus the method is actually fun).

    Stiffness doesn't need to be higher than high enough. Wooden boats normally are very stiff, impact resistance is another mater.

    The main hull is the only place where the extra structuring could be a big deal, in the amas you just don't have the scale, depends whether every bulkhead comes out of > than a reasonable increment amount of ply, then the price could escalate. On the main hull, out of the typical 10 bulkheads, you have floatation in the bow, 2x beams, rear cabin, transom, rudder. That is 6 without any for wires or spars, which may or not double. You also have a typical 2 levels of transverse stringers, where you don't have those you have hefty glass/epoxy fillets. Overall, there is little additional structure in a CM hull for stiffening the skin. Obviously in cored SF there would be less need than in the foam boat.

    That was sorta the point of CM, the recognition that vs the SF scantlings the addition of some skin thickness from 7-9mm would double the panel stiffness, and allow a more neutral distortion of the skin during fold up.

    Ply boats are faster to fair than any others, including KISS, I have seen J and S Brown fair a whole 24 footer in under 2 hours, R is even more legendary, I assume these are typical numbers for pros. You don't get a popped from a mold look, but you get a look nobody would complain of. If you want to micro pimp the finish for racing, you really don't have a faster option in any system. Fairing a boat is exactly the same problem as fairing drywall. You need to know and follow and complete each step, totally, before moving on to the next. If you want workboat finish you do a standard drywal level 4 finish, for racing, you are talking a level 5 + polishing. The fact people have no idea what they are doing, accounts for a lot of the problems.
     

  15. groper
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    groper Senior Member

    Prices I have were for here is oz, where Corley lives!

    Your fairing comment is completely at odds with what I've seen. Ply is not the easiest to fair, foam is. Most of my kiss panels need no fairing at all, paint goes straight on.

    Stiffness is controlled by foam thickness, only use what thickness you need and no more, and you save money at the same time. Foam boat is always lighter and thus faster, a pretty important factor considering it's a racing boat!
     
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