Laminating over balsa, new core construction

Discussion in 'Materials' started by gtflash, Jun 18, 2013.

  1. gtflash
    Joined: Jun 2006
    Posts: 128
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: uk

    gtflash Senior Member

    Good afternoon. Now the house is finished I now have time for my project. She is a 8.5m twin stepped rib boat and as been pretending to be a fish pond for some time in my garden.

    Boat had damage early in its life and a very poor repair was made with additional stringers and lumps of plastic. The damage and repairs were stuck in the 1st 6metres of boats length, were not straight and had extra bog to fill the voids, which then became waterlogged. This entire area was a giant ballast tank.

    Now I have researched the boats layup, and as a race boat she was deliberately made one layer of 650 less than the production models. I have removed the ballast tank and intent to fit a smaller tank of approx 150 litres, I have also removed all the add on stringers so she is now effectively the same as the production models but with one layer less.

    I originally intended to just build up the extra layer, then I considered creating a foam sandwich construction but availability is poor near me and i was worried about air pockets. If possible I'd like to bed a balsa core down, then overlay with epoxy bi-axial to make her above normal spec but without too much extra weight.

    Does this sound feasible? Reading boat strength book it seems inner skin of a cored sandwich can be thinner than outer, but would I have to match that ratio of inner to outer laminate thickness or can I apply the minimum layup to waterproof the balsa, encapsulate it and seal the bilge area. I hoped to not apply more than 2 layers of 450g bi-axial, tabbed off balsa by 6" into sound hull. But I don't know how to calculate that as correct. This area is entire running surface from bow backward to 1st bulkhead which forms petrol tank. Approx 6m back from bow

    Any help appreciated
     
  2. gtflash
    Joined: Jun 2006
    Posts: 128
    Likes: 0, Points: 16, Legacy Rep: 10
    Location: uk

    gtflash Senior Member

    To help explain. a few pictures.

    Deck cut
    roof removed from tanks
    stringers removed

    All those stringers were extra, tabbed in to form the poor repair. The most outboard of the running surface is the 2 main stringers, which are in a normal build from this manufacture. The port side had more laminating and as a result has left a hollow where the stringer was. I managed to take out vast amounts of material and almost level it out, so the laminate is approx equal on both sides.

    Just to confirm, these boats dont usually have a core on the hull, just the deck. This is where I would like to beef it up, if recommended
     

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  3. nota
    Joined: Sep 2012
    Posts: 30
    Likes: 2, Points: 8, Legacy Rep: 24
    Location: miami

    nota Junior Member

    I would not use balsa in a bilge ever
    it can rot fast in a deck in a bilge even faster
    if you must core use strong no rot or water absorbing foam

    is the boat oil canning or actually cracking or why all the repairs ?
     
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