Large Depressions in Hull

Discussion in 'Fiberglass and Composite Boat Building' started by SailingWithFriends, Jan 16, 2021.

  1. SailingWithFriends
    Joined: Jan 2021
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    Location: Sydney, NSW, Australia

    SailingWithFriends Junior Member

    This is a nice yacht design called a RL24 which has been sitting on the wrong trailer for many years causing depressions all along the hull from the rollers being situated on structurally weak areas. The actual hull was made in 1976 out of a single section of hand laid FRP. The hull is not a sandwich composite. The hull has ribs as the strengthening strategy. The actual general stiffness of the hull shell is a little more than a Laser and the structural design is much the same as a Laser. The keel line is the strongest part of the hull. The damaging rollers are halfway between the keel line and the chine line. The yacht for 1976 is a lightweight flyer weighing around 1800 lb all up. There was around 1100 of these built in Australia and the USA.

    Given I'd like not to fill all these large depressions which would add a fair bit of weight is there another approach?
    Can heating the thermoset polyester with a hot air gun and un-deform the depressions work?
    Any thoughts from anyone who has fixed this type of problem before?
     
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    You need to heat the entire area all the way through to about 180F or a bit higher to make it move easier. A heat gun won't do it, heat lamps can/might work.

    Once it is straightened you need to support it so it stays straight, then glass it on the inside with a core or stiffiner so it doesn't move again.

    A beam is placed on the outside and spaced off the hull slightly, a hole is drilled through the beam and the hull. All thread is run through the beam and hull, heat the surface and tighten the nut until it moves into position.

    More than one beam may be needed to pull the concave surface back into shape.

    You don't necessarily need to heat it, frequently you can force it back into shape without heat.

    You didn't say how big the dips are.
     
    fallguy and bajansailor like this.
  3. SailingWithFriends
    Joined: Jan 2021
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    Location: Sydney, NSW, Australia

    SailingWithFriends Junior Member

    The dips range from 1 to 2 inches deep with a elliptical depression width size from 4 inches to 24 inches usually maxing out when they encounter a frame, so the bigger ones tend to be in the forward sections of the "chinish" area of the bow being elliptical lengthwise 24 inches and crosswise 10 inches.
     
  4. SailingWithFriends
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    SailingWithFriends Junior Member

    How do you get the bolt and nut out afterwards?
     
  5. bajansailor
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    bajansailor Marine Surveyor

  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Do you think this has adversely affected performance, or is it just offensive to the eye ? Interesting to read ondarvr's report of this, first time I have read of this remedy, but it sounds like a lot of work to me.
     
  7. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    If the vessel has been sitting on the trailer long enough to deform the hull, I’d be wary of the distinct possibility of other problems not yet discovered.
    A hull that light probably did not deform under its own weight, but possibly had help from collected water, which almost always means there’s rot in the structure.
    1976 was a long time ago, and “marine age” may make it much older...
     
  8. ondarvr
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    ondarvr Senior Member

    You can leave the nut in place, or don't glass over that exact spot until later.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    yes, it may have had "help" from water collection. You need to do a full audit of all aspects.
     
  10. ondarvr
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    ondarvr Senior Member

    Thats the easy way if you can get to both sides. Otherwise you just start filling it and then glass over it.

    I always liked getting it back to as close to the original shape as possible.

    Then with it strengthened on the inside you don't need to worry about it again, at least in that spot.
     
  11. ondarvr
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    ondarvr Senior Member

    A ton or two of water sitting in a hull for a few years can create some strange shapes.
     
  12. SailingWithFriends
    Joined: Jan 2021
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    SailingWithFriends Junior Member

    Here are some photos... not the greatest as the boat is still sitting on the trailer. I put a bit of 4x4 under the keel line to to relieve the load on the chines, lowered the keel onto a supporting board and dropped some of the rollers down. You can see some pink marks the rollers have left.
    IMG20210117185441.jpg IMG20210117185051.jpg IMG20210117185117.jpg IMG20210117185145.jpg IMG20210117185203.jpg IMG20210117185242.jpg IMG20210117185253.jpg
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Bit hard to get the effect with the photos, is there any sign of cracking where the depressions are ?
     
  14. SailingWithFriends
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    SailingWithFriends Junior Member

    No signs of cracking.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    I would be surprised if it made much difference to the way the boat sails, I think the first thing to do would be to examine all internal framing for signs of rot or delamination, it might be the case it is contributing to the deformities.
     
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