What are foiling cats made out of?

Discussion in 'Materials' started by David Cooper, Feb 10, 2016.

  1. David Cooper
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    David Cooper Senior Member

    I'm looking for a general idea of how they build the hulls of foiling cats and the materials used. I know that the Flying Phantom uses Nomex and prepreg carbon fibre, but have no idea how much carbon fibre they need to use on either side of it or how thick the Nomex is. I also know that foiling A cats are half the weight of the Flying Phantom despite being of similar size (and only carry one person and a lot less sail, so they don't need to be as strong), but I have no idea how much carbon fibre they're using or what they're using in between as a filling. Does anyone have any inside knowledge on this?

    Clearly the answer could be complex as it will have more material in places where the beams and rudder attachments join the hulls, but I'm most interested in what they're using away from such points.
     
  2. gonzo
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    gonzo Senior Member

    You can make them out of plywood. There is no restriction to carbon fiber.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    This is the "homemade" Stealth foiler built out of plywood for the hulls:

    From my post in the "New Catamaran Foilers" thread under multihulls here: http://www.boatdesign.net/forums/multihulls/new-catamaran-foilers-51898.html



    [​IMG]
     
  4. GrahamR
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    GrahamR Junior Member

    I believe composite sandwich is the way to go. I've built several small cats <5m out of tortured or cold moulded ply and they've been good performers but not down to what I considered a suitable weight for foiling. My latest project is a lightweight 4.5m singlehander that I would like to foil (see my post), but we will see how it sails in normal mode first. The construction will likely be biaxial eglass & epoxy with a foam core and vacuum bagged, much like many production performance dinghies & cats I think. I'm still building the plug and doing research on the hull materials, keep in touch.
     
  5. David Cooper
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    David Cooper Senior Member

    [Edit: the two posts above appeared between me writing the following and posting it, so give me time to catch up with what they say and to adjust position where necessary.]

    I'm sure you can put foils on a Shearwater and fly it in a gale, but I'm more interested in boats with high performance which aren't held back by excessive weight or poor aerodynamics caused by shape restrictions dictated by plywood sheet. Plywood is certainly remarkably strong for its weight and consists largely of carbon and epoxy, so it's still well worth considering on many builds, but most of the people making high-performance foilers clearly prefer to use carbon fibre, even though it's expensive.

    My interest in this comes from my thoughts about building a new kind of boat which is shorter than today's foiling cats - they have hulls designed to be fast in displacement mode, and yet they spend most of the time flying instead where those hulls are aerodynamically poor. I want to build something shorter with wider, shallower hulls which the wind can flow around more easily. There's a lot about my design which I don't want to say anything about until I have patents on a few key things (which have very little to do with high-performance sailing but for which light weight construction is essential), but I can tell you that I will be using X foils (pairs of straight foils which can be removed easily from above, while the pitch is adjusted by rotating their cylindrical cases - these work like V foils upside down and will make it easy to do such things as dial in a bit of lift to windward when going upwind without canting a T foil like on the Vampire or heeling the boat like a Moth).

    All I'm asking for here is a rough guide as to what is done on the leading flying cats. What's the average amount of carbon cloth used in terms of grams per square metre on parts of the hulls away from attachment points to beams, cases, etc., are they shoving significant amounts of fibreglass in there as well, are they using a layer of kevlar cloth, what width of Nomex are they using, and how are they getting the weight of A cats so much lower than the Flying Phantom? Clearly I'll need to find someone to work with who knows a lot more than I do about this kind of thing before I actually try to build anything, but I'm not ready to waste anyone's time on complex calculations at the moment - I simply want a rough idea of what's currently done so that I can estimate costs and try out experiments with materials to see if it might be practical to use infusion rather than prepreg (in some way that doesn't fill the Nomex with resin) and to avoid using an autoclave. It may well be worth having a slightly heavier boat if that brings the costs down significantly, but I doubt it would be worth going so far as to use fibreglass for the whole thing when using carbon fibre cloth provides such clear advantages.
     
  6. David Cooper
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    David Cooper Senior Member

    Thanks Doug - that does make plywood look a lot more attractive than I'd thought, but they don't state the weight of the boat, and it wouldn't be easy to make the shape I want either because my hulls are all curves.

    Hi Graham - could you link to your thread please, because the forum's search function isn't locating it for me and I'd definitely like to read up on what you're doing. The boat I want to build is going to be somewhere between 12ft and 4m long, the length dictated by the accommodation - I want it to be possible for two people to sleep inside the hulls, the idea being to have something capable of long coastal voyages and the occasional sea crossing, robust enough to survive a storm under sea anchor, but also fast enough to outrun the storms. Ideally it should be light enough to carry up a rocky beach, and that's another reason not to compromise on materials if significant weight savings can be made, even if it adds two or three thousand dollars to the cost - it will make extreme trips possible that simply wouldn't be practical otherwise. I also don't want to do anything that will harm its race performance heavily - it doesn't need to be the fastest foiler of its size in the world, but there's no reason why it shouldn't come close. The plan is to have 50:50% shared lift between front and rear foils with the front foils right up at the bow, while wands will be used not for altitude control (which is already handled by the sloping of the foils) but for cancelling out boat pitch changes so that the foil pitch is kept constant. I'm thinking about putting two masts on it (one on each hull) to lower the centre of effort on the sails so that it can carry as much sail as an 18-20ft foiler without being blown over. The width will be 9ft, and with the foils working directly underneath the hulls rather than between them it should be just as easy to keep it upright as those longer foilers, but it could be blown over by a tailwind if it comes off the foils while gybing if it has a tall rig.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    Attached Files:

  8. GrahamR
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    GrahamR Junior Member

    Hi David,
    You can find my post by clicking on my profile name which gives a drop down menu, third one down is "find all posts" then it should be easy. I'm using a cross ply analysis spreadsheet to determinate the laminate schedule for my cat, it's been developed from Lloyds Register Small craft rules if that helps. The spreadsheet will give the phsical properties of the finished laminate providing the properties of the constituent rienforcements are correctly entered, of course calculating the forces particularly for a small multihull is not easy so a fair amount of assumption is required. You will also find most rule based approaches such as those in Dave Gerr's book are in no way applicable for small multihulls.
    There is some structural design info given in the appendices of The Glassfibre Handbook by R H Waring that may be of use.

    I'm making the plug at the moment so building the hulls is still a month or two off. My project is fairly conventional, just a small A cat with an asymmetric kite to keep me on my toes, for blasting around on the Tamar River and as I said on the post, the possibility of foiling at some time in the future. Because I'm building a plug and female split moulds this will give me the option of building lighter carbon hulls at some future point.
    Good luck,
    Graham
     
  9. David Cooper
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    David Cooper Senior Member

    Hi Doug - it's certainly interesting to see the insides of those plywood hulls. Are you now thinking of building Fire Arrow out of plywood instead of carbon fibre?

    Hi Graham - I've found the book easily enough at Amazon, and I've also found a number of programs that look as if they do the same job as whatever it is you're using, but I'm still going to put more trust in testing experimental parts to destruction to make sure they're not too overstrong or too close to failing. Knowing exactly what some of the top builders are using in different places for boats of this kind would help to reduce the amount of experimentation required and thereby keep down the costs. I'm surprised at how hard it is to get hold of such basic information.
     
  10. Stumble
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    Stumble Senior Member

    My guess from working backwards is that there is about 10lbs of nomex, and 40lbs each of carbon and epoxy. But honestly if you can't figure out the laminate schedule of your design then you need to farm it to someone with the engineering background to do the number crunching.

    Modern A-Cats have a complicated layup schedule to keep weight down as much as possible, and different areas of the boat have radically different laminate schedules. The bows for instance are single layer carbon, where the transoms can be anything from beefed up solid carbon to nomex cored depending on the expected loads.
     
  11. David Cooper
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    David Cooper Senior Member

    Thanks Stumble - any information of that kind is helpful. I'm still making lots of changes to the design which make big differences to how much strength will be needed where, so what I most want at this stage is to acquire an intuition for how much material is needed where and roughly how it will be arranged - when people have done this kind of thing for a long time they have a lot of knowledge of the many similar things they've already built and the way they were structured, and they can draw upon all of that knowledge as they modify their design in their head to understand the likely costs and gains of all those little changes without having to get a calculator out at every step. They also have a strong understanding of how the fibres will most likely need to be aligned, and by the time they're actually working out the fine detail with a computer, they probably already know most of what it's going to tell them. They'll also know if there's an error in the maths because the result will look wrong: knowing what already works is much better than designing in a knowledge vacuum. There are also places where the maths doesn't tell the full story or the forces aren't estimated well enough, so some pieces may need to be beefed up more - again it is experience that counts, and I want to take every shortcut possible to gain from other people's experience rather than doing beautiful calculations to create something that may promptly snap in half or be much heavier than it should be.
     

  12. jehardiman
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    jehardiman Senior Member

    "What are foiling cats made out of?"

    The Sternest of Things!

    [​IMG]

    <Sorry couldn't resist a straight line....>
     
    Last edited: Feb 16, 2016
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