Boston Whaler type construction

Discussion in 'Boat Design' started by Saqa, Dec 19, 2014.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    No sign of Flomanse's router cut foam, the stuff is expanded in-mould. PU foam has only modest physical properties compared to PVC, but the convenience of being able to pour it into the void, in situ.
     
  2. Saqa
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    Saqa Senior Member

    Is mold requirements the only significant downside of the Whalers construction method?

    Regarding the delamination issues. After reading Par's comment yesterday I have been googling this issue. Looks like there are a lot of whalers out there from around the 80s that have this issue to some extent. I am sure that there are actually a lot of whalers sold which prolly leads to higher statistics. But is this delamination also a problem with the new generation? Most of the google hits seem to be the "classic whalers"
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd say it would likely be mechanical failure within the foam as much as de-lamination, it seems to stick well enough from what I've seen.
     
  4. PAR
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    PAR Yacht Designer/Builder

    It does stick well enough, but as you'd think after so many cycles, it tends to delaminate. I've found it's not just an age or build era issue, so much as an amount of use concern. I've repaired some that were on a few years old, yet they'd had issues. Come to find out all of these are boats used daily or very regularly, meaning it's a cycling issue and the foam only has so many before it craps the bed.
     
  5. Saqa
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    Saqa Senior Member

    Thanks Par, that's good to know. We discussed a stretchable polyester fabric for sheathing some time ago. I wonder if a sock with foam strip wireframe was placed into the mold and 8lb PU poured into that would adhere better to the fabric weave. I think glass/epoxy would attach quite well to the other side of the fabric

    For simple practical use to make a slim pontoon hull I envision a half pea pod type female mold in concrete with the excess rise simply trimmed away and two such plugs epoxied together with maybe csm as filler
     
  6. PAR
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    PAR Yacht Designer/Builder

    To make a core a viable possibility, it's about compressive strength (8 pound is good) and peel strength with whatever you use as a skin/sheathing. I don't think a stretchy/flexible sock would be helpful, as the sock fibers would yield long before the resin does, so something's going to give. The idea is to have the skin and resin with similar modulus, so they fail roughly at the same time, offering the best from each.
     
  7. Saqa
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    Saqa Senior Member

    That makes sense. Another possibility I can think off would be denting the cured core all over with a board with lots of thick nails hammered through with 5mm protruding the other side. Prime the core with neat epoxy, fill the holes with structural epoxy putty then sheath wet on wet with bi or triax. Or would all that be wasted effort?
     
  8. PAR
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    PAR Yacht Designer/Builder

    Wasted effort. Either you have the peel strength or you need it. Asking the relatively flimsy core to do more then it can, well . . . The core is simply a spacer for the skins, which needs good peel and compressive qualities.
     
  9. Saqa
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    Saqa Senior Member

    Hmmm, fair enough, I thought the 8lb be good structural core and just be needing enough skins for some impact resistance and sealing. Will be a coosa skeleton embedded/anchored in the foam core though. If 8lb is not enough then 16lb be too heavy too
     
  10. PAR
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    PAR Yacht Designer/Builder

    If the boat is designed right, you don't need a skeleton, especially something as heavy as Cossa. The whole point of sandwich structures is light weight, while still having the strength and stiffness necessary.
     
  11. Saqa
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    Saqa Senior Member

    Par, I dont know if I am going in the right direction, its just things that I am examining

    I want a flat open deck with rails and good stability. Heading out and back through heavy chop, average 25-30 knot prevailing tradewinds. Out to the the fringing reefs and back, around 30mins to the first large reef that has breakers then following the chain stopping to cast heavy 200g lures back to the break and smashing them back in to the boat, max 4 people. Two of them casting with 8' rods

    Mooring is behind my inlaws farm in the bay with the same winds. In the wet season it floods almost every week and a lot of logs and debris gets washed into the bay, it can be like a washing machine. Also the wind can push boats into each other. During the wet season storms are frequent and occasional cyclones to cover as well. Intention is to pull the boat up but still lots of flying branches and stuff that can smash things

    I am exploring a cat with flat bridgedeck and centre console driving position with a pair of 40s. Minimum 20' x 10' and slender hulls to slice through the chop for daily comfort. Solid core that can take a pounding and no natural materials that can rot if I miss a deep nick in the finish

    Welding polyethylene sheets to make the hulls will be my next thing to ponder after working out the viability of the foam materials. I have ruled out alloy build

    I was thinking along the lines that a coosa skeleton anchored into the solid foam core will be good to mount the deck to also made from coosa
     
  12. ondarvr
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    ondarvr Senior Member

    Lets see, the CG does not require 4# foam, they suggest it saying it's more water resistant. BW's do not use block foam, the foam is injected into the cavity. Pour foam breaks down over time, the correct mix done at the correct temperature will be stronger and last longer, but it will still break down eventually (The correct conditions are not always in place in production). The cell walls are rather rigid and begin to fail, the more that fail the faster it breaks down. Then you have freeze & thaw cycles in some parts of world and the foam deteriorates even faster once any water gets to it.

    The CG requires that if foam is used it needs to be fuel and oil resistant, but doesn't require foam, only that if the chamber is punctured the craft must remain afloat. Foam just happens to be an easy and cost effective way to do it in production.

    To fill a cavity with 8# foam would be very costly and heavy, most builders use 1.65 to 2 LB foam for floatation.

    The best way to use a pour foam is use a plastic bag in the cavity to be filled and fill it with the foam. Also have the cavity accessible so if and when the foam degrades it can be replaced easily, it may be a little difficult to design it this way, but it helps to eliminate the shortcomings of foam.
     
  13. markstrimaran
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    markstrimaran Senior Member

    Any thoughts on polyisocyanate foam vs polyurathane
     
  14. johnhazel
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    johnhazel Senior Member

    There is a fairly new core "soric" which you can use to make sandwich construction using vacuum bagging methods.

    https://www.youtube.com/watch?v=7dt...FB1BFE14&playnext=1&playnext_from=PL&index=12

    More traditional foam core is used in our racing canoes. They are vacuum bagged Carbon Fiber - foam -Carbon fiber and take quite a beating. 18.5 ft long and under 30lbs 2 person boats.

    http://www.savageriver.com/canoes/racing/jd-pro-2

    there is also Nidacore

    http://www.lbifiberglass.com/NIDA/nida.html
     

  15. Saqa
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    Saqa Senior Member

    Yeah I am looking at alternatives too. I looked at Nida but seems there are others at a better price and sizes, Carboncore Polypropylene honeycomb doesnt seem too bad at $72 a sheet for the 19mm 8' x 4'

    At the moment its
    Solid foam core vs Coosa sandwich vs honeycomb sandwich vs welded HDPE
    I wonder which of the 4 be the toughest, maybe HDPE
     
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