Lightest and Strongest Hull... What Materials and How??

Discussion in 'Fiberglass and Composite Boat Building' started by kyboatbuilder, Jan 12, 2008.

  1. JohnMc
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    JohnMc Junior Member

    A thin OK1088 marine ply with epoxy and a couple layers of fabric has got to be one of toughest laminate schedules.
  2. cahudson42
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    cahudson42 Junior Member


    This is going to sound retrograde, but for a 21' Bass Boat why not just use 5086 0.125 Al?

    Weld it up as a giant 'box beam'(s) and you will have one heck of a strong boat.

    I'm looking at an 18' in Delftship and the Al 5086 material weight is maybe 300 lb. By the time you add yourself, the motor, fuel, etc. - whats really going to be the performance difference between a 300 lb AL Hull and some exotic Hull that maybe weighs what - 150 lb?

    What am I missing here?

    Last edited: Jan 16, 2008
  3. Jimbo1490
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    Jimbo1490 Senior Member

    Aluminum is stiffer than E-glass, even if the E-glass is layed up as skins on a foam core with epoxy and vac bagged. That's why he'd have to go with at least S-glass or carbon skin sandwichto one-up a good aluminum boat. But stiffness (as in bending, panel stiffness) is driven by the thickness of the panel, so you'd still have to address that with an aluminum design. The box beam is one way of doing that; sandwich construction works with aluminum skins, too.
  4. longliner45
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    longliner45 Senior Member

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    FAST FRED Senior Member

    Just be sure it does not have to go back to a factory & autoclave to repair minor damage.

  6. tinhorn
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    tinhorn Senior Member

    Years ago I played with some 3D fabrics skinned with a Kevlar/graphite weave and one-ounce mat, with VE resin filled with microspheres. Unbelieveably light and rigid. (Not on boats, though - prototype electric car bodies.)

    I can't even remember the name of the fabric, but I understand it's no longer available.


    I remembered! Parabeam.
    Last edited: Jan 26, 2008
  7. eponodyne
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    eponodyne Senior Member


  8. petereng
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    petereng Senior Member

    Probably the lighest and strongest hull would be a kevlar/thermoplastic laminate. Twintex sell glass/polypropylene material and its toughness is hugh. The process would go as follows. Layup dry kevlar, interleave with perforated PET. PEEK or Nylon film. Place vacuum bag over it, put in oven under vacuum and let the plastic melt through the laminate.

    This can be done with glass as well but kevlar is less dense and stiffer.

    Eglass 2550kg/m3, E=70Gpa. Kevlar 1440kg/m3, E=110Gpa

  9. the1much
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    the1much hippie dreams

    last night on some discovery channel thingy,,,they showed a new stronger "high tech" carbon fiber,,i think it was C.something , something,,,,,great help aint I ;)
  10. marshmat
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    marshmat Senior Member

    The thing is supposed to go 80 mph? In what sea state?
    Carbon fibre does not take kindly to impact loading; I would rule it out here because this boat is going to hit the water HARD when it chine-flops off a nice whitecap. You probably want something that will flex a bit on impact rather than cracking. To get a carbon laminate thick enough to avoid structurally damaging levels of deflection in such a scenario, you'd negate much of the weight advantage carbon has in hulls subject to more uniform loading and more gradual changes in loading.
    In pure composite methods, I would lean towards multidirectional Kevlar/S-glass hybrid fabrics set in epoxy, sandwiching Core-Cell (or Nomex, if you're adventurous).
    In metal, you could probably get similar results with a well-engineered welded aluminum structure.
    If you aren't averse to the use of wood, perhaps a strip-plank / epoxy composite method should be considered, again using Kevlar/S-glass fabrics.
    Properly engineered, you could probably see roughly comparable weight and strength using any of these methods. Note that "properly engineered" is critical in an application like this.
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  11. rwatson
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    rwatson Senior Member

    'Gut feeling' indicates aluminium., Especially since you are on a budget.
    Timber is great, but you are doing heavy work in rough seas, and it isnt that tough for rough use.
    Aluminium has another great advantage - no surface coating. On timber and composites, the paint/coating/gel coat finish that keeps the water out can cost a significant amount of the actual material and needs constant maintenance on a working boat.

    With aluminium, you weld, you are finished - and its very robust. For that size boat, it would be as light as you need.
  12. petereng
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    petereng Senior Member

    Composites do not require painting or gel coating to keep the water out. Paints and gel coats are just resins with pigments in them, so thay are the same as resins with fibres in them. Resins are plastics which absorb water, just like timber but to a much lesser degree. The water absorption is a problem for polyester resins but not vinyl ester or epoxy resins. Polyester resins break down with prolonged contact of water (hydrolysis & osmosis)

    Peter S

    With composites you bond and you are finished.
  13. grob
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    I have tried this and it didn't work, I don't think there is enough "resin" in the twintex to get the kevlar to bond properly. You could peel the kevlar off the laminate after it had cured. You would need to ask the Twintex people to make up a special batch especially for this purpose.

    That said I think that Twintex would be the lightest and toughest material possible, and there is probably no need to add kevlar.

    edit .. that said its not a process suitable for homebuilding.

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  14. Pericles
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    Pericles Senior Member

  15. rwatson
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    rwatson Senior Member

    Composites DO REQUIRE COATING - for UV protection mostly and to keep water out as they all absorb water, albeit slowly
    When is the last time you saw a raw GRP boat?
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