Hull delamination on a Laser.

Discussion in 'Boat Design' started by kroberts, Jul 19, 2010.

  1. kroberts
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    kroberts Senior Member

    Hi,

    Got a friend with a Laser sailboat. We were using it today on Lake Michigan and when putting it back we discovered that the upper hull and lower hull are separating. It's most obvious right around the front, but I noticed that the sides show evidence of some sort of caulk and under that it's also delaminated. I'm guessing maybe half the perimiter is not quite attached. Looks like the same latex stuff used in bathrooms to seal around the tub. The boat seems to take on a bit of water, but I think it's not too heavy after you drain it. It's upside down on a rack at a harbor now, so I guess I'm wondering what needs to happen in order to fix it.

    My inclination would be to scrape out the seams between the two layers for an inch or so, maybe with a dremel or even a hand tool, and then fill again with epoxy and some fumed silica or maybe some West System 404, mixed to pancake batter or maybe a little runnier. Then clamp it and leave it for a week.

    I guess the thing I need to know is whether I really need to take the hull apart and clean anything out in there. Or maybe replace foam or whatever. Or do I just epoxy the seams and leave it alone?

    While I'm thinking of it, what do I do to recondition the hull? The fiberglass seems to be a bit faded on the bottom and there are definite scratches. And the corners are all banged up too, might as well fix that too while I'm at it.

    Looking for recommendations.

    Thanks.

    Thanks.
     
  2. kroberts
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    kroberts Senior Member

    After doing some research, I discovered that "delamination" is not quite the word I should have used. The hull is separating from the deck.

    I now realize that I probably shouldn't use epoxy to bond them together again, but rather some sort of putty or removable adhesive. I have no idea what though, and still don't know if I should try to remove it all and separate the parts or just try to squeeze more adhesive in there.
     
  3. Jeremy Harris
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    Jeremy Harris Senior Member

    IIRC the hull and deck on Lasers are bonded together using a flexible polyurethane adhesive, probably Sikaflex. My guess is that to effect a good repair you'll need to try and completely separate the hull and deck, clean up the mating faces and re-bond.

    It might be worth getting a definitive statement from the manufacturer on the type of bonding material used, as it may possibly be polysulphide based, rather than polyurethane based. It almost certainly won't be silicone or acrylic based, as most domestic caulking materials are, as these have pretty poor mechanical properties when compared to polyurethane or polysulphide based adhesives.

    There are alternatives to Sikaflex that are a little cheaper and seem to work as well. I've used polyurethane automotive body panel adhesive in place of Sikaflex and found it to be near identical in performance.

    Jeremy
     
  4. kroberts
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    kroberts Senior Member

    Jeremy,

    Is this something I need to take it to the garage for or can it be done in a couple hours on the rack at the marina?

    I guess that if I need to contact the manufacturer I can probably get that info from them, but I would rather also have some sort of experienced real human give an opinion.

    Thinking about it, I may be able to use a hook knife rather than a dremel for what's left of the adhesive. Just guessing.

    Another option I might need to consider is a temporary fix for the summer, and then fix it once it's back in the garage. If it was my boat I'd haul it back and fix it right away, but it's not and the owner doesn't always take my advice.
     
  5. Jeremy Harris
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    Jeremy Harris Senior Member

    I've just done a bit of digging around for you. The hull deck joint would have originally been bonded with 3M 5200 polyurethane adhesive. Some people have done repairs using epoxy resin filled with a suitable filler (like colloidal silica) but if it were me I'd stick with using polyurethane.

    It seems that separating the hull and deck is a big job, as it means breaking the bond at the centreboard case and mast step, so the most expeditious way to effect a good repair might be to just scrape out as much of the old adhesive as you can, make sure the boat is dry internally and then go around the seam a small bit at a time, squirting in adhesive with a gun (the stuff comes in tubes that fit a caulking gun).

    It'll be a messy job, but should be straightforward enough. Apparently it's very common for Lasers to come unbonded at the hull deck joint after a fair bit of use.

    Jeremy
     
  6. kroberts
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    kroberts Senior Member

    Jeremy,

    I just got done searching the Laser Forum and came to pretty much the same conclusion. Mostly that separating the hull from the deck is a Really Bad Idea since it's not my boat, and since it's on a rack at the marina.

    Supposedly there's an inspection port somewhere, but I have no idea where. This is NOT a pre-production boat since it has a serial number, so presumably I won't have that foam problem. It all seemed to drain out fairly quickly, so I don't think there is any compromised material in there.

    I had been thinking of fumed silica since I have about a cubic foot of it, but I think I'll stick with 5200. I wonder if I should use masking tape to protect the area I don't want the adhesive on? Or is that a waste of time? And is one tube of the stuff enough, or do I need several? Can I get this stuff at any marine supply shop or do I need to order it? I guess I should try a search engine, huh? :)

    My dremel has a cord, so I don't know if I can use that. I can definitely get some hook knives and various other digging tools though. And I wonder if I can use some sort of hypodermic style injector to get the adhesive into the crack more easily? And I wonder if I should chip a bit, then glue, then chip a bit -- or if I should chip it all out and glue all at once?

    Thanks for your help.
     
  7. kroberts
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    kroberts Senior Member

    Also, can I expect to successfully do this on a boat rack? It's basically on 2 pieces of square tube, front and back, a couple feet from each end. Typical storage for small sailboats at a marina I think.

    My worry is that the removed adhesive will allow the boat to flex, and then when it's glued it will stay in the wrong shape. It's a PITA to get it to a garage, considering the logistics of things in Chicago.

    Thanks.
     
  8. Jeremy Harris
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    Jeremy Harris Senior Member

    If you do a short length at a time I think you will probably be OK doing it on the rack. The nozzle on the tube of adhesive should be thin enough to fit into the joint to squirt the stuff in. Masking off areas around where you're working would be a good idea - this stuff is very, very sticky and is a bit of a pain to work with.

    I've found that polyurethane adhesives can be wiped off reasonably well using alcohol. I've used propyl alcohol with success for cleaning the stuff up, but probably any alcohol would work and shouldn't damage the hull.

    Jeremy
     
  9. wdbeyer
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    wdbeyer Junior Member

    Ken, most Home Depots carry 5200 for a lot less than you"d pay at a marine supply store. After cleaning out the old stuff and getting the new into the seam, maybe use a spanish harness or two to clamp the hull tight to the deck. Just a thought. Good luck.
     
  10. kroberts
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    kroberts Senior Member

    Jeremy,

    OK I will do that. But do you mean do a short length, let it cure completely and then do the next short length? If so it'll be quite awhile to get the boat done. How about do a foot, leave a foot, do another foot and so on, all the way around, and then finish up next week? And FWIW the whole front of the boat seems to be disconnected, so I suspect it won't hurt much to hit that all at once. Or am I wrong?

    wdbeyer,

    I already found the links to Home Depot. I also saw one that claimed Wal-mart's marine area had it for cheaper yet. Will check both, there are both within a couple minutes of my house.

    I have no idea what a Spanish harness is. Google only gets me Spanish-English translation for pages. I have some clamps though.

    Thanks.
     
  11. wdbeyer
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    wdbeyer Junior Member

    Ken, its a knot used with a loop and a wooden rod, used by some sttich and glue boat builders to clamp the sides together. I can't find an example rite now to point you to. I suppose you could use some ratchet straps, or clamps if you can get them to hold. I'd do the whole seam if you have the means to clamp everything together and leave for the time it takes the 5200 to cure.
     
  12. tom28571
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    tom28571 Senior Member

    Haven't read the whole thread but it is not necessary nor realistically practical to separate the hull from the deck since the mast socket and cockpit is also glued to the hull bottom. This is a common problem with Lasers and other boats of the same construction. Turn the boat over on saw horses and work your way around the joint. Pry the separated areas a bit further open with screwdrivers and force in some sealant/adhesive into the space. Just let the joint close up on its own accord with no clamps. Done this on several Lasers with success. Any good waterproof sealant/adhesive will work.

    Of course, dry out the joint first.
     
  13. kroberts
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    kroberts Senior Member

    wdbeyer,

    Search as I might I can't find a spanish harness knot. Love to hear about it.

    Tom, I guess there are the following questions left:
    1. How dry is dry? This thing is stored upside down in an outdoor fenced off area on a rack. Rain and dew and all that, probably. But the days have been hot, and chances are we wouldn't get there before noon. So a half day of drying, would that be out of line?
    2. I can bring a dremel and an extension cord, but I don't know if there's power there that we can use. Is there some sort of hand tool that can scrape that old adhesive out the best? A hook knife or linoleum knife or something similar?
    3. How many tubes of 5200 do we need to do this, considering neither of us have done anything like it at all?

    I guess that's all.

    Thanks.
     
  14. tom28571
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    tom28571 Senior Member

    If this Laser is typical, there is no problem with strength as there is probably still a majority of the deck/hull lap joint intact and only a small portion of the joint that has delaminated. I would not use 5200 although it would be OK. I like "Boatlife", 101 or PL Window And Door sealant for jobs like this. Never had a Laser where one 11oz tube was not sufficient.

    If you pry open the bad areas and leave them open so that they can dry for a few hours in the sun, that should be OK. After The major leaks are taken care of, I like to use a vacuum cleaner on pressure to slightly pressurize the hull and look for more leaks with soapy water. Don't overdo the pressure as it is easy to distort the hull.
     

  15. kroberts
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    kroberts Senior Member

    So I don't need to dig out the old adhesive or re-do the entire joint all the way around?

    I've done a lot of vacuum clamping of 12 to 20 foot hovercraft hulls using a shop vac, so I am fairly familiar with the risks of too much pressure. Thanks though.
     
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