Hull flexing on 49' Norm Cross Tri

Discussion in 'Multihulls' started by Paul S Hamilton, May 26, 2021.

  1. Paul S Hamilton
    Joined: May 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: Sea of Cortez

    Paul S Hamilton New Member

    Hi All,
    We've got a 49' 1985 49' Norm Cross that we've had for a little over three years now, and have about 22 months on the water in the Sea of Cortez. She's cold moulded western cedar with fiberglass on top.

    Overall the hull seems to be in good shape.

    She's been through some rough weather, but was just tested in her first blue water wind storm in the Pacific. There were about 3m waves every 1-4 seconds and 30kts sustained wind. We went mostly away from the waves (and ended up abut 80nm off track), so avoided most of the worst of the weather. A couple observations:
    -Every time a wave hit the inside of the port ama, the side bent in, ribs and all, maybe 1cm. No damage was evident, though
    -When we were all done, we had a crack in the fiberglass under the stbd wing, but the wood seems unaffected

    We've had some other issues with the fiberglass skin splitting, but have chalked that up mainly to not fitting quite right on the trailer, and there are some predictable flexion points that have cracked.

    My big question is: How much is this boat supposed to flex?? Is it a worrysome sign for a hull to flex so much as to see it like that? Do we expect there to be some fiberglass cracks now and then or is it a sign of something structurally wrong?
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Flex can be OK, but cracking much less so. It appears to have flexed beyond its limits, which could be a design or build flaw, or being exposed to stresses beyond the designed limits, or some combination of the three. Having a marine surveyor look at it seems a wise move. One thing about GRP, you can relatively easily repair it, and add more where weaknesses have been exposed, but you need an expert opinion on what the best remedy is, and first hand observation will trump any other assessment.
     
  3. garydierking
    Joined: Sep 2004
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    Location: New Zealand

    garydierking Senior Member

    After 20,000 sea miles in my 37' Searunner, I found the same thing on the inboard forward side of one of the floats. That particular area takes tremendous abuse from breaking waves and it did crack one of the plywood frames. It's a good area to reinforce although I would not have known about it from the outside. If your tri was glassed with polyester, you can expect to have some of it come loose. I lost some on the underwing but nothing structural.
     
  4. Paul S Hamilton
    Joined: May 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: Sea of Cortez

    Paul S Hamilton New Member

    Got it, thanks for that. We will be getting a focused survey done as soon as we pull out in San Carlos. Fingers crossed!
     

  5. Paul S Hamilton
    Joined: May 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: Sea of Cortez

    Paul S Hamilton New Member

    I don't know about epoxy vs polyester. Since these are backyard builds from plans which are no longer available, it's hard to know what the original specs were and if they were followed. Do you know is there any way to determine if there's epoxy or poly by examining it?
     
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