Cracks in window frame. How to fix?

Discussion in 'Multihulls' started by mrybas, Mar 4, 2018.

  1. mrybas
    Joined: Jun 2017
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    Location: East Coast or Cruising

    mrybas Junior Member

    Or maybe cut out the wooden frame, make a temporary form attached around the opening, and wrap the opening with glass unis?
     
  2. rberrey
    Joined: Oct 2010
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    rberrey Senior Member

    Free advice from Ad Hoc + cost of material = good deal .
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    If you had a separate piece, that covered the region you show in that image, is the way to go.
    As also noted, make a template from the window. Make the wooden insert very smooth from one piece of wood that extends over the region you indiacted, not joined or scrafed. Make sure the radius is very smooth with no score marks.
     
  4. UpOnStands
    Joined: Nov 2015
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    UpOnStands Senior Member

    Not a great idea IMHO. You are just introducing another interface that will have to tied into the boat.
    The other corners are not cracked so build up the cracked frame by running 2 inch FG biaxial strip around the inner/outer edge and then heavy biaxial flat on both sides of the opening; up to the roof on the top, to the door frame on the inner side, to side wall and say 6 inch at the bottom.
    Use just the FG/epoxy. its good enough.
     
  5. mrybas
    Joined: Jun 2017
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    Location: East Coast or Cruising

    mrybas Junior Member

    I removed 4-5” of the wood from the frames and replaced with unis. Then glassed band-aided the corners with unis and biax.
     

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  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The reason you're getting the cracks is poor panel design, when the boat was built. Having the plywood seams in the locations they are, causing stress risers and this is simple engineering 101, obviously ignored by the builder. The solution is to grind down the affected areas at a 12:1 taper, for 2/3's of their thickness and replace the laminate.
     
  7. Jimbo1490
    Joined: Jun 2005
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    Jimbo1490 Senior Member

    What PAR said. And when you lay that glass on the dressed/scarfed cracks, you must pay attention to the fiber orientation; the fabric should be on the 'bias', that is at a +/-45 wrt the crack or the window frames. This is critical for a couple of reasons. One is that in such an orientation ALL the fibers will participate in carrying the loads through the cracked area where as with a 0/90 orientation only half the fibers are doing anything; the fibers parallel to the crack are essentially useless. The other reason has to do with the load spreading that comes with this orientation vs more load concentration with 0/90. You will have more waste fabric with this orientation but that's just the cost of doing it right, IMHO.

    Jim
     

  8. mrybas
    Joined: Jun 2017
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    Location: East Coast or Cruising

    mrybas Junior Member

    Hi Jim,
    Used one layer of unis across the crack and 2 layers of 1700 with the fibers at 45 def to the crack.
     
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