Patching a cut in hull

Discussion in 'Boat Design' started by Clayton Bishop, Jul 9, 2012.

  1. Clayton Bishop
    Joined: Jul 2012
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    Clayton Bishop Junior Member

    I am new to this forum and want to thank you guys and girls in advance for any help you provide! I have already used some of your threads to help me thus far but wanted to join to get more information. So thank you again!

    I have a 1976 tri hull quachita bass boat that I have recently tore the floor out of because the foam was wet. Well while cutting out the floor I put two 3 inch long cuts in the front of the hull that went all the way thru and I need info on what to use to fill them in with? The cuts ar 3 inches long by about 1/8 inch wide (the width of a saw blade). Again thank you gusy for any help!!
     
  2. gonzo
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    gonzo Senior Member

    You should grind the area and laminate fiberglass over it. Ideally, you will do that from either side.
     
  3. Clayton Bishop
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    Clayton Bishop Junior Member

    Thank you!

    I also have some spots where I am wanting to fill in some voids that were created by removing some of the foam. Is there an apoxy that I can use to fill these?
     
  4. PAR
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    PAR Yacht Designer/Builder

    How big of voids do you need to fill? If more then shallow divots, scratches and such, then you'll want something other than epoxy. Are you looking to replace removed foam?
     
  5. viking north
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    viking north VINLAND

    God yet another wet foam mess. My favourite tools for such, a sheetrock saw and a flatbar. It's like rowing 100, miles patience and one stroke at a time gets her done. Another handy tool i use, a typical woodworking shop dust collector with a 4 inch hose intake blowing into a construction size trash bag set up on the collection end. Does a fantastic job with anything from dust to 31/2 in. cube sized foam chunks. The setup in the photo helped remove truckloads of wet and dry foam at an amazing rate.I also use this same tool as a fume extractor when glassing in confined areas and when welding.
    When repairing hull punctures as you have described i find it is best to glass over the inside first. This gives a solid backing for bevel grinding, glassing and filling the outside .
     

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  6. Clayton Bishop
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    Clayton Bishop Junior Member

    Yes PAR I plan to replace the foam with pool noodles as they are made of closed cell foam and the original foam did not appear to be of a structural importance. So it sounds like grinding and fiberglass is the best way to patch the buts in the hull, thanks guys!!

    The voids I was speaking of are just places where the old board that I tore out meets the sideboard of the boat and I was wanting to shoot something in there to fill the void between the new board and the sideboard of the boat. Thanks again guys!!

    Yes cutting out the foam was a dirty nasty job. It was not as soaked as I had thought and I was surprised at how little was in there, granted this is only a small fishing boat but still was surprised by how little was present.
     
  7. rwatson
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    rwatson Senior Member


    Great info there Viking.

    But POOL NOODLES !!!!!

    Good grief - what a bad choice. How can you fair that, and what about all he voids you will be creating ?

    Its rare that foam isnt structural in a boat design - otherwise it wouldnt be in the middle of the glass.

    You may want to submit some photos of the location to experienced builders to make sure you are doing the correct and safe thing.
     
  8. SamSam
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    SamSam Senior Member

    I think he's talking about flotation foam.
     
  9. rwatson
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    rwatson Senior Member

    I pictured those metre long tubes of plastic hollow spaghetti with a 1" hole in them.

    If that is what is meant, the fact that they are round, hollow and very soft makes them a really poor core material.
     
  10. Clayton Bishop
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    Clayton Bishop Junior Member

    I can try to post pics but no promises, I am not very good at that sort of thing :)
    Yes I am talking about flotation foam which was found underneath the decking that I tore up that was rotten. The peices of foam came off in big chunks pretty much fully intact. They were approximately 2 inches thick by 24 inches long by about 8 inches wide. There were about 4 of these "chambers" with this foam in it. My main hesitaion with the poor in foam to replace what was there is the cost.. it is 139.00 bucks a gallon that makes 1 cubic foot. Any other thoughts or ideas on what to use instead?
     
  11. SamSam
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    SamSam Senior Member

    I agree the swim tubes would make a poor core material, although Boeing could make it work for a few billion $.
    But he's not talking about core foam, he's talking about flotation foam which in that old of a boat I believe has no structural purpose.
    It does make me wonder though if flotation foam is used for structural purposes. I've never thought about it but it would make a lot of sense to kill two birds with one stone like that.

    1 gallon at $139 makes 1 cubic foot? No, you have that wrong.

    I've never seen a guy scramble so fast as when my friend crawled way back under his deck and inadvertently dumped 10 times too much foam for the space into the bilge. I suppose he would have been killed if he hadn't moved so fast. It was pretty funny, I can still recreate it, all the screaming and hollering, clunks and thumps and swearing as he reappears feet first in full retreat.

    Plastic soda and water bottles are suggested a lot nowadays as a substitute for flotation. Sometimes chunks of building insulation foam will be used to roughly fill in spaces. Sometimes people don't use any flotation. The foam retaining moisture and preventing air flow ventilation is probably what rotted the deck in the first place.

    If you want flotation, you might be better off leaving your bilge open and ventilated (with some soda bottles or insulation if they wouldn't block ventilation) and pack the sidewalls below the gunnels and the transom under the splash well instead. What you want is that if the boat fills with water, not only will it not sink, but almost as important is that it floats somewhat level. If it doesn't sink but the weight of the engine pulls the transom down, you end up with just the tip of the bow sticking out of the water. If it floats level, even though only a few inches above the surface, you can still be "in" the boat more or less and it isn't such a chore to hang on. If just the bilge is full of flotation and not the sidewalls, if the boat flips, all you have to hold onto is the bottom, which by design is smooth and slippery with no handholds to hang onto.
     
  12. Clayton Bishop
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    Clayton Bishop Junior Member

    Thank you Sam Sam... The info was very helpful! I appreciate your time.
     
  13. SamSam
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    SamSam Senior Member

    As for those 3" cuts, grind them from the inside in an area about 2x5", with tapering sides about 3/4 of the thickness of the hull. Fill up the area with enough patches that increase in size to bring them a little bit higher than the inside surface. Once that's set, go to the outside and do the same thing, sand it flush and finish.
     
  14. rwatson
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    rwatson Senior Member

    As I understand it, there was substantial glass on both sides of the bad foam.

    That = structural. Period. It may very well be part of the flotation specs. That is very common. Especially "3 inch long cuts in the front of the hull"

    If saving a few bucks is the name of the game here, then we are in the wrong game. When you are 2 kilometres off shore in building waves, the few lousy dollars saved in doing a botched job seems really stupid. If you do an estimate of materials, you might spend $50 on foam, $80 on goo, $50 on glass and additives plus "sand" paper and cleaners etc. If this is too much, you are playing in the wrong sandbox.

    You dont need to use expanding foam - its not what is required here. What you need is some high quality marine foam sheet, cut into suitable shapes, and patched together with epoxy or other polyester resin with something like Cabosil to thicken it into a substantial goo.

    You can then fair the rough structure, and build up the glass both sides.

    The best approach where you are able, is to leave the outside, polished, flat, faired layer intact, and cut chunks out of the inner liner - where high class finishing and fairing is neither needed or necessary. Just glue the sheet foam to the outside hull skin with thick wodges of thickened resin. Epoxy will do a better job, as it will stick to the existing hull much better.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Pool noodles or pourable two part polyurethane foam will work great, as I understand your needs. You've just removed the floatation foam, which isn't structural in most cases. If you use pourable foam, don't cut it, just fill the void and leave the skin intact. If it bubbles over and you have to cut it (not uncommon) then seal the cut foam with a few coats of epoxy. Pool noodles are much cheaper, but you usually have 30% - 40% voids around and inside these tubes, which is self defeating to a degree.

    If I have to use pourable foam, I tape in some thick corrugated cardboard around the inside of the area the pourable foam is going, then I line the cardboard with a plastic bag or sheeting. Next, I pour the foam and let it cure. Once hardened, I pop out the foam, with the sheeting and cardboard still attached. I peel off the cardboard, often leaving the plastic in place. The result is a foam block that is form fitted, but slightly smaller then the area. This allows for expansion and contraction and permits me to shim the foam block in to position to let air circulation around the foam. Any condensation can avoid the foam and is able to drain off or evaporate out.
     
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