Filling Manufacturers Hole in Bow

Discussion in 'Fiberglass and Composite Boat Building' started by benjiwoodboat, Jul 4, 2008.

  1. benjiwoodboat
    Joined: Jul 2008
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    Location: Marthas Vineyard, MA

    benjiwoodboat New Member

    I have removed my bobstay chainplate, which was inserted into a hole in the bow and glassed in from the inside of the hull. I'm replacing it with an externally mounted design. To fill in the original slot, whats the best technique? Do I need to grind down from the inside in the 8:1 ratio and fill layer upon layer with mat? It's very tight there and on an inward curve, which makes the 8:1 technique more tricky. Can I simply grind back to some clean fresh glass and fill it with a thick 406 or cabosil mix, and glass mat behind that. It's about an inch thick at the bow there. And while im at it, whats the difference between 406 and Cabosil?

    Heres some pics of what im workin with...

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    thanks,
    ben
     
  2. tinhorn
    Joined: Jan 2008
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    Location: Massachusetts South Shore.

    tinhorn Senior Member

    While I like to taper both sides (inner and outer) on a patch job, there have been times when it was just impossible. I'd then focus on making the repair on one side only - 8:1 taper, flawlessly prepared surface, and using cloth whenever possible. I wouldn't even consider putty for this patch if approached from just one side. (I've made a lot of repairs and modifications, but very few on boats. Wait for a second opinion.)

    I'm not familiar with 406. Always just mixed Cabosil into my resin.
     
  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    If you've already removed the metal, just make sure the slot is clean and fill with epoxy/high strength filler. That area is ultra-strong. If in doubt, add layers of mat/roving on the inside to increase thickness. Ensure the outside is sealed with epoxy. I wouldn't over-engineer it.
    More important is to properly support the replacement plate, which I assume is a set of straps properly oriented in line with the bobstay. They should be bolted through plywood back-up pads and a triangular insert just below the nuts wouldn't hurt either.

    Alan
     

  4. benjiwoodboat
    Joined: Jul 2008
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    Location: Marthas Vineyard, MA

    benjiwoodboat New Member

    Thanks alan and tinhorn.

    For replacement have been going back and forth between machined bronze straps and a cast bronze piece similar to what was there before in shape, but externally mounted. Still undecided, but I have been working on a casting pattern.
     
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