Large Depressions in Hull

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

  1. rxcomposite
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    rxcomposite Senior Member

    I use heat gun all the time. It works.
     
  2. ondarvr
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    ondarvr Senior Member

    You already mentioned how you use it, which is different than in this situation.
     
  3. ondarvr
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    ondarvr Senior Member

    I'm not sure there is clear communication on this.

    It is very difficult to heat a large area of a thick laminate with a heat gun. On a small thin laminate it can be done, it's not particularly a good way to do it though because you can very easily overheat the surface and damage it.

    On large thick laminates a heat gun is even a worse option because of the amount time and care needed to do it, if it can be done.

    If you lower the temperature of the gun, it takes that much longer to heat the surface. And that's only if you can get the entire area warm at the lower setting.

    With a light you can set it back 3 feet or so and leave it, when you come back the entire area is warm all the way through.

    Polyester is fairly good insulator, it takes a while for the heat to transfer all the way through a thick laminate.

    We teach methods that are reliable and consistent, methods that are likely to fail at a high rate are advised against.

    In a shop the heat gun is even a worse option. Paying someone to hold a heat gun for an hour or so to heat the surface when a light can do it better and the employee can be doing something more productive doesn't make sense.
     
  4. rxcomposite
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    rxcomposite Senior Member

    What? No heat gun can survive that. Are you teaching that?
     
  5. rxcomposite
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    rxcomposite Senior Member

    Ondarvr- You are out of topic. The issue is a dimple the size of a fist and you are talking about large area and thick laminates.
     
  6. ondarvr
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    ondarvr Senior Member

    He said they are from 2" to 4" deep and up to 24" wide. A hull will be relatively thick. And if it's been sitting that way for an extended period of time the depressions may have taken a set.

    My description of what to do first takes into account that they may come out easily, the next step is the extensive heating.

    I used to do this stuff all the time, it had to be done quickly and correctly. As I mentioned before, when doing this for a paying customer it needs to be in a way that you know will reliably yield a good result on the first try.
     
  7. ondarvr
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    ondarvr Senior Member

    Frequently you couldn't get to the backside, so it was all done from one side.

    If they were large, you may need to cut it in the center so it would pop back into shape.

    If it had only been sitting in the deformed position for a short period time it may return to the correct shape easily. Occasionally there were parts that had been sitting deformed for years, these typically needed much more help in returning to their original shape and staying that way.
     
  8. rxcomposite
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    rxcomposite Senior Member

    What was the name of your company again? The one that teach "methods that are reliable and consistent, methods that are likely to fail at a high rate are advised against."
     
  9. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    What a pissing match.... Just sand the gelcoat off in the depressions, rough up the surface for bonding, fill the dips with an epoxy based light filler (not bondo). Sand it smooth to the level of the original glass. Apply a light layer of bid over the top for protection, still with epoxy. This will harden the surface compared to paint directly over filler. Do final sanding, prime, sand, paint final color. I'm assuming there will be no anti foul on a trailered boat. Would probably have to paint the entire bottom to get it to match nice if you are fussy, but its not that big a job. Roll and tip should be fine.

    Then take those rollers off and get some bunks installed with some flex in them covered in marine carpet. You will never have the problem again and can continue to enjoy your boat.
     
  10. rxcomposite
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    rxcomposite Senior Member

    Not exactly. It degenerated into mine is bigger than yours. We all contribute to the thread in the spirit of the forum. It is still up the OP to accept or dismiss our 2C worth.
     
    Ad Hoc likes this.
  11. gonzo
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    gonzo Senior Member

    That is a lot of work and expense, when a few sticks and a heat gun will do the job. Also, adding filler is creating stiffer areas which leads to stress risers.
     
  12. ondarvr
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    ondarvr Senior Member

    His wish was to not fill it, so the answers went in that direction.
     
  13. 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.
    4. If no result fill the depressions with a light filler as directed.

    Alternative No1, take the whole lot to the tip, get a loan and buy a Elliot 7!
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    What's to stop using suction to drag the depressions out ? You just need the right appliance ? When out where you want it, leave it in place for a time.
     

  15. wet feet
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    wet feet Senior Member

    Nothing, just as long as you have the equipment-and a former to pull it to.simply putting a vacuum bag over the depressions will achieve nothing.Its a lot easier to find a post than a vacuum pump.Its also a good idea to have a trailer that doesn't impose heavy point loads on a hull area that doesn't have good support inside.
     
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