Recycling GRP for transom Use

Discussion in 'Materials' started by Basjan, Oct 9, 2012.

  1. Basjan
    Joined: Sep 2007
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    Location: South Africa

    Basjan Basjan

    A stupid question maybe, but one I have to ask.

    Can scrap layers of fibreglass (eg. pieces of deck, hull, etc) be used to lay-up into a sheet for use as an alternative to marineply or other core materials?

    What would the best goo be to use, epoxy or polyester resin?
    I understand that the marriage between these two can be a bit cranky.

    How would the bond be between the old cured resin and new lay-up ?
    Would it stand the test of time or do we forsee a divorce?

    Your input and speculations please.
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    As a transom core, it'll be heavy, really heavy if all laminate. It can be done and the best resin choice would be epoxy. You can do it several ways. One would be to grind up the old boat decks, etc. in to small piece, mix with a lighter weight filler, such as "perlite" to keep the weight down, then this mixture is mixed with resin and poured into a cleaned and toothed transom cavity. This method assumes the inner and outer skins of the transom are complete and up to the tasks of bearing the majority of the loads imposed.

    Another method would be to laminate sheets of thinner material until you have a core of sufficient thickness and bond this to the hull shell with tabbing. This would be heavier then the above method, but would be stronger and you can do much of the work on a bench.

    The reason plywood is used is simple, it's fairly light for it's strength, it's cheap, it's readily available and easy to work with. It bonds very well and if quality plywood is used, can have a long life.

    The real problem with a laminate as you've described, is weight. A core like you're suggesting will be in the range of 15 to 20 (6.8 - 9 kg) a square foot at 1.5" (38 mm) thick. That's a lot more then a plywood core which will be in the 5 pounds (2.3 kg) per square foot range.
     
  3. Basjan
    Joined: Sep 2007
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    Basjan Basjan

    Thanx PAR

    I just thought it might be a usable alternative to marine ply, seeing I only need less than a SQ foot to do a small repair on my boats transom.
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Generally, unless it's plugging a small hole, transom cores aren't "repaired" but are replaced. What type of damage are you trying to address? Can you post a photo or two?
     

  5. Basjan
    Joined: Sep 2007
    Posts: 25
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    Location: South Africa

    Basjan Basjan

    I bought a 14" cubby cabin river boat and found some rot in the transom.

    Transom was constructed of three layers of ply (1/2" ply + Grp + 1/4" ply + Grp + 1/2" ply).
    Each layer consists of mutiple pieces of ply.
    The pieces overlaps the joint of the pieces in the next row (like brick work).
    Each of the pieces have been individually glassed in as there are grp between the pieces.
    The previous owner has cut down the transom for a short shaft motor and only covered the exposed ply with resin and pool coat.
    The center piece of ply (about 6" width) of the outer layer against the hull started to rot from the water getting in.
    Part of the two adjoining pieces has also started to rot, but the rot is only limited to the top corners next to the center piece.
    As far as I could establish these are the only ply affected. I have drilled two small holes right at the lowest part of the transom going in about halfway into the transom. The wood shavings came out relatively dry, no signs of rot or water. Will plug them with epoxy once I fix the rest.
    The rest of the transom seems ok as I have checked the wood on the inside of the plug holes as well. I epoxied pieces of plastic conduit pipe into the holes. These run straight through the transom so no chance of water entering there.

    I was figuring that I might be able to replace the rotten piece with the grp. I have quite a bit laying around.
    Also, I will be using a S/s transom plate over the transom for extra support and to lift the transom as I will be running a 25HP long shaft for the time being.
    Will be switching to a 15Hp as there are less legal requirements on skippers and boats running 15hp or less.
     
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