transom core

Discussion in 'Fiberglass and Composite Boat Building' started by garrybull, Jun 29, 2014.

  1. garrybull
    Joined: Nov 2010
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    garrybull Senior Member

    on my new boat im building i was going to use 18mm ply in the transom but am now looking at either seacast or nidabond.

    has any one on here used either product.

    also i see there made from polyester.

    would it be possible to make up my own using polyester resin mixed with 12mm strands of chopped mat or is it not a good idea.

    i can't find any one in the UK that stocks either product.

    i have emailed a couple companies that lit nidacore products but they don't keep the nidabond in stock.
     
  2. upchurchmr
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    upchurchmr Senior Member

    What kind of a boat? What kind of construction?
    If there are any big loads going thru it (bolts for attachment) don't use a real core with cells.
    The bolts will crush it, allowing water in.

    At least replace the core with plywood or solid lumber in the area of the bolting.

    Polyester with chopped glass is about the heaviest possible way to build a transom core. Chopped glass is significantly weaker than any other method of the same density.
     
  3. garrybull
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    garrybull Senior Member

    its a brand new tunnel cat im building.

    look in the projects section under new project and you'll see what ive done so far.

    the boat will have a 1 piece pod bolted on the back for the outboards.

    the boat is being built using polyester resins etc.

    so what about seacast or nidabond then?

    any good or waisting my time if i use it?
     
  4. gonzo
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    gonzo Senior Member

    I would recommend to stick to what the designer says on the plans
     
  5. garrybull
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    garrybull Senior Member

    i have designed the boat myself.

    just wanted to know whats best to use as the transom core.

    i normally use 2 layers of 18mm ply bonded in place with bonding paste and glassed over.
     
  6. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Actually this hull is an old Fairey shape but modded to have a tunnel hull by Garry. It should be OK too. I'd stick with heavy ply or an end grain custom panel of pretty heavy timber to avoid crushing from engine mounts and useage. Like a Balsa end grain but using say Khaya or even stronger in compression. Glass with roving for better spread than CSM or a mix of both. It is compression and long life you are after and also perhaps someone 'over powering' it too.
     
  7. garrybull
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    garrybull Senior Member

    i'll probably go down the ply route for the core.

    im thinking 2 layers of 18mm ply with each sheet bonded in and cover with csm and woven so total thickness will end up around 55mm thick and be really strong.
     
  8. ondarvr
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    ondarvr Senior Member

    Seacast and others work well, but they are a mix of several different fillers to get the right strength, weight and workability, a mix of resin and just fiber wouldn't work well.

    You may also need to use a different catalyst to keep the temperature down.
     
  9. garrybull
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    garrybull Senior Member

    i can't get seacast or nidabond in the UK so i'll probably stick to plywood and bonding paste.
     
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  10. hardguy007
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    hardguy007 Junior Member

  11. jorgepease
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    jorgepease Senior Member

    Coosa Board!!!
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    Yeah, that did come to mind. Depends on local availability I suppose.
     
  13. AndySGray
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    AndySGray Senior Member

    I agree with your idea that the Ply would be better for the clamping forces of the motor mounts.

    We have a boat too large to trailer and it stays in water most of the year.

    Transom got a few soft spots resulting from fixings for trim tabs and the like in a couple of years (even with 5200 on screws).

    OK what passes for marine ply here is fairly poor...

    With hindsight I would have used ply at the top and nida downwards so no wood below the waterline.
     
  14. garrybull
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    garrybull Senior Member

    im using that for the decks in my cat.

    you can't use that in a transom really as engine bolts would probably crush it.

    on my boat im fitting a double outboard pod which is being bolted in place so i need to use ply.

    none of the engine bolts will be seen as there all internal to the pod so the ply shouldn't get wet.

    i'll be using plenty of sikaflex when bolting the pod in place and plenty round the bolts.
     

  15. jiggerpro
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    jiggerpro Senior Member

    Mr Garrybull;

    Y would suggest using corecell then making holes of adequate dimension in it where the crushing forces may appear bolts, engine mounts and so on ..with a router or jigsaw then placing the foam horizontally and with holes sealed the bottom side with tape and fill the holes (maybe in steps to avoid heat buildup) with your preferred mix of resin and other fillers, this way yopu will get the light weight witthout the rotability of wood while having a non crushable transom where it matters ..... that is how I will be doing it in my custom boats, needless to say that the holes mentioned should not be tight to the bolts diameters but more like an oblong shape that comprises groups of bolts. PM me if there is anything I have not explained clearly
     
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