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Correction of warped GRP Hull

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  • Correction of warped GRP Hull

    Hi there! I am thinking about ways for straightening a large GRP Hull i purchased some years ago. I just resumed Click image for larger version  Name:	20220116_103350.jpg Views:	0 Size:	82.2 KB ID:	158019Click image for larger version  Name:	20220116_103342.jpg Views:	0 Size:	59.6 KB ID:	158022Click image for larger version  Name:	20220116_103428.jpg Views:	0 Size:	79.2 KB ID:	158018Click image for larger version  Name:	20220116_103308.jpg Views:	0 Size:	54.3 KB ID:	158020Click image for larger version  Name:	20220116_103412.jpg Views:	0 Size:	66.7 KB ID:	158021 working on it and found the upper and lower hull beeing slightly out of shape. The hull has been cut at the waterline. The deck bends upwards both bow and stern and the lower hull is now a bit wider at the broadest point so the deck would fall right through it. I remember the overall fit not beeing perfect back in 2018 when it arrived, but not THAT bad.

    My idea: removing any surplus material from the inside to achieve a consistant wall thickness, rigging the hull halves up and forcing them in shape by taping and/or some sort of jig assembly, giving it a good hot water washing and varefully apply heat by heat gun.


    Best regards, Jörg

  • #2
    You'll probably get different advice from different quarters. Heat can work to get a hull straight, but the GRP does tend to have a memory and will very likely move again over time. You need to be careful too, as heat can cause blistering of the gelcoat.

    Many hulls are pulled from the tools when they're still a bit too green. In addition there can sometimes be some distortion in the original tooling, which is then built in to every casting.

    Polyester hulls can be particularly bad, as the resin shrinks a lot more than epoxy as it cures. Also little or no model submarine hulls are post cured, as it takes a lot of expensive kit to do it properly. That makes it more likely that the hulls will move over time unless well clamped/jigged in place, especially if they're stored somewhere hot. Zip ties work well to keep hull halves aligned and clamped when in storage.

    Bonding in an inner frame would help to keep the top aligned. Such a frame could be made from something like epoxy glass sheet and bonded in with a good epoxy or modified acrylic adhesive.
    Last edited by Subculture; 01-16-2022, 05:48 AM.
    Time to DIVE IN!


    • #3

      thank you! I will then try taping it back to shape first, no heat applied, and leave it for a week. The hull itself is very heavy and could have deformed from bad storage. I do not believe it was "green" since the previous owner did a lot of work . What might have an influence is that he cut out the missile doors for a quad launcher, but closed them up again later, prior to selling the kit. He used a lot of filler and the waterline was seoerated already.



      • #4

        Tape her in tight, use gently the heat of a hairdryer, let her cool down, you may have to do that several time, you mentioned she has a thick hull, this can be easely done with a epoxy hull, polyester is a different story.
        Did the same procedure with the hull of the ype XVII, she also had some issue's due to long storage.
        When done, let her stay a few weeks taped together, after a quick cooldown with some water.
        When everything fitts, build a internal structure to keep her that way, when cutting her at the waterline you have weakened the shape of the boat, this is common at waterline cuts, when done it the best to store it inside the mold itself, if you don't have a mold, keep her stable with a internal structure.

        Last edited by MFR1964; 01-16-2022, 08:29 AM.
        I went underground


        • #5
          I have run into this problem and here is what I did. In my case I had a badly twist destroyer hull. I found that by bracing the hull into position, it took quite a bit. I made a strong back and clamped everything in two axis. Once the hull was braced into the correct position, vertically, horizontally and with 80 lbs of lead along the keel to keep it straight, I applied my heat gun to the INSIDE of the hull. I used moderate heat. I continued applying the heat until I could hear the hull actually change it's set. After letting it cool competely, I eased off the bracing to check the twist and fund it to be completely releived to within 3/32". It appeared to be symetrical as well. I re-applied my external bracing and added internal bracing inn the form of my deck edge strips and deck beams, all the while retaining the external bracing. When I was done and removed all the bracing, the hull was true.


          • #6
            Thank you Manfred and KumaDog for your hands-on descriptions! I am now confident i'll be able to make the Whiskey fit again!

            Cheers Jörg