Large Depressions in Hull

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

  1. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    It takes a long time for it to take a set if it's formed into a warped shape, if it sits for years that way it frequently doesn't straighten back out on its own.

    It's the same when you straighten it back out, it can take a long time sitting back in the original shape to stay that way. And it may pop back to the warped position if pressure is applied.

    This all depends on many variables, the exact laminate schedule, the exact resin, how well the resin was cured, how long it sat that way, etc.

    If it was a small area and a thin laminate, a heat gun may work, but you need to be very careful because you can easily overheat the resin.

    A light spaced a long distance from the laminate can be left in place for hours. This will thoroughly heat the laminate all the way through with less chance of doing damage.

    You need to use an IR temp gun to monitor the temperature.

    However you force it back into shape, it needs to be held in that shape for as long as possible, plus supported from the backside or the warp may return.

    On a thin laminate a suction cup could work, on a hull laminate probably not, it would depend on the amount of vacuum and the length of time you left it there though.

    I normally needed to fix something like this quickly and permanently in one try. Customers don't like failed repairs, so you start with the method that is most likely to succeed every time.

    If it was mine, I'd block the hull up using stronger points on the hull right away and leave it sit while I was doing other work just to see what happens.

    And on a sailboat hull I wouldn't worry about it unless I was going to compete and thought it might really make a difference in my results.

    As a beginner your limited abilities would easily outweigh whatever disadvantage the warp created, if there was any at that speed.
     
    Last edited: Jan 19, 2021
    bajansailor likes this.
  2. rxcomposite
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    Location: Philippines

    rxcomposite Senior Member

    Depends on the resin you used. Can be unsaturated or unsaturated. Can be thermoplastic or thermosetting.

    If thermoplastic, heating it would need some cajoling to push it back to shape. Use a wood stick as the surface is hot. If thermoset, heat it and it pops back to shape. It has a memory.

    We made a lot of repairs on our isopthalic resin boats. If there is a dimple after fabrication (improper support), we just heat it and it pops back to form. Some parts we have to remove by heating. It distorts upon removal but heating it again while unstressed and it pops back to normal.

    We used also polyimide resin (similar to nylon) on HT cored panel. Somebody kneeled on it and produced a fist sized dimple. It was gone in 3 days before we could touch it.

    Nothing to worry about. It is an easy fix.
     
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  3. gonzo
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    gonzo Senior Member

    I don't think that boat is built with a thermoset polymer. That would be true of a rotomolded kayak or dinghy.
     
  4. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    I've only known rotomoulded hulls to be made from thermoplastic resins-maybe things are different on opposite sides of the Atlantic.I've only known fibre reinforced moulded hulls to be produced from thermosetting resins which soften when they reach a critical temperature,but not to the point where you would ever use them for injection or rotomoulding purposes,although they can be injected before they polymerise.

    I do wonder about the possibility of using a vacuum to pull out these deformities as it isn't something I've ever done.The closest being to return a partly laminated 60 foot hull that had pre-released back to the mould surface while the rest of the laminate was added.It worked,but I had the advantage of a stiffer mould to hold the shape.For this trailer sailor you would have to create a stiffer outer shell to pull the hull to.Either a heavy laminate taken off an identical hull without the distortion or maybe a small strip planked former would probably work.I think its all a bit academic as a plywood pad and a post with a wedge or two would probably suffice.I suspect that the effect of the depressions on the performance of the boat is less significant than a couple of fumbled tacks.
     
  5. gonzo
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    gonzo Senior Member

    It will go back to the original shape, or close enough to it, by just pushing it from the inside with a stick. There is no need to complicate things with vacuum systems and molds.
     
  6. SailingWithFriends
    Joined: Jan 2021
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    Location: Sydney, NSW, Australia

    SailingWithFriends Junior Member


    Yes that's what I've done on point 1 already and a great idea.
    Yes on point 2 I am competing. That said in a new class I start with old sails and a bit of gear on the boat and only start spending $ and lightening things on the boat if I'm not competitive.
     
  7. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    paint it with a dazzle paint scheme and no-one will notice ! ( the depressions, that is, they will be distracted)
     
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  8. SailingWithFriends
    Joined: Jan 2021
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    Location: Sydney, NSW, Australia

    SailingWithFriends Junior Member

    So here's the plan as suggested by the responders.
    1. Take the load off and leave it alone and see what happens. Go sailing, racing etc. Don't fumble tacks... Come fourth in the National Titles...then
    2. Heat the area and experiment with a heat gun, IR sensor and IR lamps use sticks and wedges inside the cabin to hold the heated areas in their new correct position... See what happens.
    3. If no joy then... drill, bolt and pull out the depressions with a bit of 4x2 on the outside of the hull and glass the inside to hold the new shape.

    Alternative No1, take the whole lot to the tip, get a loan and buy a Elliot 7!
     
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  9. rxcomposite
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    Location: Philippines

    rxcomposite Senior Member

    Me: "You bought a new boat? What happened to the first one?"
    You: " It got wet"
     
  10. gonzo
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    gonzo Senior Member

    My heat gun goes up to 1200 F. It is enough to set a boat on fire.
     
  11. SailingWithFriends
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    Location: Sydney, NSW, Australia

    SailingWithFriends Junior Member

    It may be that the rate of heating is too fast and wont penetrate all the material without burning...
     
  12. ondarvr
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    ondarvr Senior Member

    This is it.

    The heat gun puts out a great deal heat in a small area. You need less heat distributed evenly over the entire surface.

    This lower level of heat needs to be uniform from the exposed surface through to the backside of the laminate.

    Lights can be spaced back a few feet and be left that way safely for hours to achieve a complete heat soak.
     
  13. rxcomposite
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    rxcomposite Senior Member

    You constantly move the heatgun over a large area. Or increase the distance. That way you don't burn it. Surface should be hot to touch but not enough to discolor paint or gelcoat.
     
  14. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Anytime a customer insists on using a heat gun I tell them to put their hand on the part right where they're heating it and keep it there, if it's too hot for your hand, it's too hot for the part.

    Heating with a light is far easier and more effective, the thicker the laminate, the better a light will work.

    Heat guns frequently cause more problems than they help with.
     

  15. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    That is incorrect. Heatguns have nozzles that can concentrate the heat in one spot or spread it to a large area.
     
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