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Thread: Cold Molded Hull Cracks?

  1. #1
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    Default Cold Molded Hull Cracks?

    Backstory: I have a 15' cold molded Marsh Cat (Joel White) catboat that I bought two years ago. It is not new - my recollection from conversation with the former owner is that he was the second owner and the boat is 15+ years old. For various reasons I didn't get to use it much last year, so it's been on the trailer by the side of my house for 12-15 months. I've been careful to keep it covered and not allow water to pool in the bilge.

    Last weekend I started to get her ready for the summer, and I noticed the following cracks in the paint on her interior hull, maybe 15" from the transom on both sides - of which only the worst one is pictured here. Please excuse the dirt - I was wearing gardening gloves and felt at the cracks.

    20190512_111147.jpg

    So my immediate questions were: 1) What does this mean? and 2) How freaked out about it should I be?

    I did a little more looking, and it seems that this area is right under the aftmost bunk supports on both sides. This is the trailer and configuration that came with the boat, and so far as I know she has been sitting on these bunks her whole life. However, closer inspection revealed that she doesn't seem to be sitting on them evenly, as shown below. I don't recall seeing this gap last year, but I can't be sure it wasn't there.

    20190512_111201.jpg

    She does not really sit on her keel on the trailer, which seemed a little odd to me at first but according to the previous owner was fine - after all, she probably hasn't ever been on another trailer. There's a plank that runs crossways under her keel roughly in line with the aft ends of the bunks, as seen in the following picture. Note that she is not touching the forward roller.

    20190512_111117.jpg

    So I'm thinking that I should modify the trailer to support directly under her keel and just use the bunks to keep her from falling over. This would have the benefit of allowing the bunks to be reduced in length and upward sweep aft and allow more easily loading and unloading from the trailer. To support the keel, I was thinking something like a 2x6 with rails blocked up on the trailer frame and faced with UHMWPE or similar slippery plastic. Is this the right approach?

    What should I do about the cracks showing in the interior hull? strip the paint and apply new coats of epoxy? Is it likely a sign of deeper damage?

    Any help is appreciated.

  2. #2
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    Default Re: Cold Molded Hull Cracks?

    my immediate thought is that she should rest on her keel primarily but I will defer to other more experienced minds.

  3. #3
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    Default Re: Cold Molded Hull Cracks?

    Better support on the trailer is always a good thing. I just bought an old dinghy which needs lots of work, but one of the biggest problems is where the bilges collapsed because the boat wasn't supported properly on centerline. I agree with your trailer strategy. I further offer that the side bunks should be well outboard and at the turn of the bilge, where the hull form is stiffest and strongest. You know, the same place they put jack stands in the boatyard.

    It isn't unusual for the surface veneers of wooden boats to check and crack. The tree is never dead until it burns, and there is always more shrinking and welling than the pundits admit. We have added very light glass veils ( like 1 0z / ft^2 stuff you buy for model airplanes) to the outside of many classic cold molded dinghies to make this go away without adding a ton or weight or surrendering the varnished hull finish.
    Years ago I learned that there is something at the bottom of every crack. Take a small disc sander ( 2-3" Dia Rolock or equivalent) and grind the paint off. Make sure nothing looks amiss, that things are dry and not damaged. I usually epoxy a light glass strip ( 4-6 ox at +/- 45) over the wound and squeegee it down flat with a piece of plastic film. With luck the surface is very close to the original, and can be lightly sanded and painted.
    SHC

  4. #4
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    Default Re: Cold Molded Hull Cracks?

    Well, exactly what SHC said. Most boats want to be supported mostly by the keel on the trailer, doing otherwise is asking for trouble. By the way, I've used those slippery plastic bunk covers. They work great.
    -Dave

  5. #5
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    Default Re: Cold Molded Hull Cracks?

    A wee cold molded boat will not get bent or distorted by a bad trailer set up like a carvel, clinker or ply boat.
    The only person who knows how well a cold molded boat is built is the builder. She may be unsheathed to save money , time, labor or all three.
    She may be resin starved somewhere in the “matrix”.
    But yes, I would deal with every single crack. At least until some time has gone by.
    Lets hope she is cedar, this is when one does not want spruce or pine for molding.

  6. #6
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    Default Re: Cold Molded Hull Cracks?

    I'm not sure what material the hull is, but I do have a photo (from the former owner) of the hull exterior before she was painted:

    IMG_1806(1).jpg

    The former owner told me that he glassed her outside up to the water line, so I would guess the rest of the outer hull hasn't been glassed. I don't have any information on what kind of glass was used. It seems like perhaps the first things to do are figure out the trailer and strip the paint to see how the cracks look. I'll also take a closer look over the entire boat to make sure I don't have any other lurking issues.

  7. #7
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    Default Re: Cold Molded Hull Cracks?

    The interior cracks appear to be about perpendicular to the waterline. (Am I interpreting your photo correctly?) I would expect the interior layer of a cold molded hull to run longitudinally or +/-45. Do you know the lay-up schedule? I would be inclined to remove the paint around the cracks to get a better look.

  8. #8
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    Default Re: Cold Molded Hull Cracks?

    I expect those cracks are due to shrinkage of non-glassed veneer, especially because some of the outer veneers are flat grain so it's likely that some of the inners are too.

    If the keel roller is moved up or the bunks down more of the weight will be carried by the keel. Like Bruce I don't think that's all that important on such a light hull, but it would still be good practice, most notably on bumpy roads and more so if it's not glassed anywhere.

    I seriously doubt that the current support system had anything to do with the cracks in the paint.

    Not sure what I would do about those cracks though. It would be nice to fill them with something squishy then seal it up well, but maybe stripped there will be more info.

  9. #9
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    Default Re: Cold Molded Hull Cracks?

    my guess is that this outside planking is WRC. It can and will come in a variety of color shades, such as what you've got. The cold molding I recently did had as much variation

  10. #10
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    Default Re: Cold Molded Hull Cracks?

    This is why builders often glass the hull of cold molded boats. Telegraphing of the seams is very common in boats that were not sheathed in f'glass. The sheathing can be very light.

  11. #11
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    Default Re: Cold Molded Hull Cracks?

    Thanks for all the responses, everyone. I'm relieved to hear that this probably isn't a major problem - or at least not a major structural problem. I did not have time to strip off any paint last night, but I took a quick look this morning and noticed few other areas on the hull exterior with suspiciously similar seeming cracks. This is in the middle third of the hull right under the rubrail - for some reason it's showing upside down.

    20190515_084314.jpg

    There are some other larger - maybe 18" - faint cracks like the one at the right of the picture above.

    @DeanP, these are running at 45 degrees or so from the centerline, as is the layer on the outside of the hull. I also took a picture of the hull where it meets the transom to show the hull layup layers (below). I would say the hull seems to be something like 3/4" thick if this is representative. It also appears that part of this area has been glassed:

    20190515_084443.jpg

    From the comments, it seems like maybe the best long-term solution is to glass the topsides with light woven fiberglass? In the short term, strip the paint and fill the cracks with thickened epoxy? Would colloidal silica be the right thickener? Or should this just be dealt with piecemeal by applying fiberglass strips over the cracks as they appear?

  12. #12
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    Default Re: Cold Molded Hull Cracks?

    I think you need to do some exploratory sanding and scraping and see how big a job you have on your hands. It may well be cheaper in the long run to take the hull down to wood, let it dry out for a while, then glass it entirely than to try to do it piecemeal. It's only a 15 footer, and if you do it right you'll have a great little boat that will last a long time.

  13. #13
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    Default Re: Cold Molded Hull Cracks?

    Thanks for the photos and explanation. It makes more sense now. The photo of the transom (with the blade in the foreground) appears to show a pattern that suggests there may be cloth on the transom and/or the outside of the hull?

    I'm building a 15' cold molded boat and plan to put Xynole fabric on the outside - primarily to add some toughness to the West Red Cedar plies and prevent the print-thru others have described.

    Good luck, you have a nice looking boat.

    Dean

  14. #14
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    Default Re: Cold Molded Hull Cracks?

    I would not use thickened epoxy as you want to get glue down to the bottom of the cracks. I like the Robb White get it hot first and let the cooling suck the epoxy in.
    SHC

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    Default Re: Cold Molded Hull Cracks?

    Seeing the bit of black stain in the planks, I fear water has been creeping in.
    Best practice , imo, sand her to bare wood, two layers of dynel when dry.
    Heating epoxy , or wood, ... I do not like the idea. Yes, it makes the epoxy thinner, but it kicks off too fast. The cure is already happening when hot. Consider the opposite, if epoxy is cold and wet for hours rather than minutes, it may soak in better.

  16. #16
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    Default Re: Cold Molded Hull Cracks?

    So the weather wasn't super cooperative yesterday - overcast with bits of sun until about 5PM, then rain . Nevertheless, I was able to spend a few minutes to take the paint off a couple of the cracked areas. Here's what I found:

    This is the center crack pictured in the first picture of the OP. It's hard to tell, but it looks like the whole thing is under a layer of epoxy. Possibly cracked epoxy.

    20190515_194014.jpg

    20190515_194050.jpg

    These are cracks shown in the first picture of post #11. The blistered looking crack is the larger one.

    20190515_194457.jpg

    20190515_194445.jpg

    20190515_194423.jpg

    As previously mentioned, I bought the boat used and it's a decade or more old. It was originally bright finished on the topsides and interior (although it's possible that the interior was never fully finished and was left with just epoxy). When I bought it I had a local boatbuilder remove the old damaged finish on the topsides and interior and paint them. This boatbuilder has experience with mostly smaller boats and kayaks built with plywood and epoxy, but no specific experience with cold molding (neither do I, for that matter). My understanding was that the stripped hull was recoated with epoxy prior to paint, but I'm starting to think that this did not happen - or at least wasn't as thorough as I'd like.

    The coamings and transom, etc. that we wanted to keep bright were not fully restored (bleached, etc.) but were stripped of old varnish and revarnished to keep them from deteriorating further. The boat was dry and stored indoors while the work was done.

  17. #17
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    Default Re: Cold Molded Hull Cracks?

    Quote Originally Posted by wizbang 13 View Post
    Seeing the bit of black stain in the planks, I fear water has been creeping in.
    Best practice , imo, sand her to bare wood, two layers of dynel when dry.
    Heating epoxy , or wood, ... I do not like the idea. Yes, it makes the epoxy thinner, but it kicks off too fast. The cure is already happening when hot. Consider the opposite, if epoxy is cold and wet for hours rather than minutes, it may soak in better.
    Below is a photo showing more of the transom. There are a lot of leftover watermarks and darkening from previously neglected finishes on this boat - all the remaining brightwork and a lot of the topsides prior to painting were in this condition, but no actual rot was found at the time the work was done. As mentioned above, the wood wasn't fully restored, but the old finish was removed and new varnish was put on to prevent things from getting worse.

    All of which isn't to say that there couldn't be some rot somewhere, but don't think there is - at least I hope not.

    20190516_083939.jpg

    My experience with epoxy is very limited, but I'd be reluctant to apply much heat to the boat for fear of causing additional expansion and cracking. Maybe that's not a reasonable concern?

  18. #18
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    Default Re: Cold Molded Hull Cracks?

    Judicious application of a heat-gun and sharp (SHARP!) scraper is a good skill to acquire. This boat looks like a good candidate for a thorough do-over, down to wood, fix anything soft, sand it fair, then glass and epoxy, and then paint.

    Could we see some pix of the whole boat?

  19. #19
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    Default Re: Cold Molded Hull Cracks?

    I don't have any up-to-date pictures of the whole boat, but I'll post some as soon as I have a chance to take a few. It might be tomorrow.

  20. #20
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    Default Re: Cold Molded Hull Cracks?

    Rain prevented me from getting out and taking pictures yesterday or this morning, but I did dig up a photo from last year and one of how she looked when she was delivered to me:

    Here she is impersonating a motor launch:

    20170722_150354.jpg

    And here after the work mentioned earlier in the thread was completed:

    refinish9_053.jpg

    refinish9_055.jpg

    refinish9_056.jpg

    refinish9_058.jpg


    As it turns out, the builder that I had do the work kept a photo log of sorts, which can be found here:

    http://www.keakayaks.com/refinish9/refinish9c.php

  21. #21
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    Default Re: Cold Molded Hull Cracks?

    I think moisture is still getting into the hull laminates, and they are moving relative to one another. That is the source of the cracking.

  22. #22
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    Default Re: Cold Molded Hull Cracks?

    Quote Originally Posted by Rob Hazard View Post
    I think moisture is still getting into the hull laminates, and they are moving relative to one another. That is the source of the cracking.
    Thanks for the feedback. This seems like a definite possibility, assuming that ambient humidity would be enough to cause this to happen - these cracks appeared while she's been on her trailer.

    As I understand based on the replies in this thread, the fix is to strip the paint, remove any damaged wood, reseal with epoxy and fiberglass or dynel, and repaint. This would be done for sure at each crack, with perhaps the better long-term solution being to strip the whole boat and glass the whole thing. Is that an accurate summation?

    Regarding damaged wood, am I right in thinking that discoloration does not necessarily mean rotten or damaged? If the wood is discolored but dry and hard is it safe to glass over? By which I mean I won't be promoting further damage under the glassed area?

  23. #23
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    Default Re: Cold Molded Hull Cracks?

    Slight discoloration like weathering would be OK, but where it has turned black or gone soft you need to replace it. I would take the rub rails off and glass right up to the deck. And while the boat is upside down you could dry it out better by tenting a tarp over it and putting a gentle heat source under it, like an oil-filled electric space heater.

  24. #24
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    Default Re: Cold Molded Hull Cracks?

    As a point of reference, would you suggest removing wood based on any of the above pictures of where I removed paint from cracks? None of these areas is soft, but all show some degree of discoloration due to previous exposure.

    I guess what I'm trying to ask is how reliable is discoloration as an indicator of rot if the wood hasn't gone soft?

  25. #25
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    Default Re: Cold Molded Hull Cracks?

    Exactly where are these cracks on the boat in relation to the trailer supports, mast and chain plates?

    It looks from here that they are from the gunnel, and go towards the keel yes? But wider at the top. Ever cracked a bit of wood over your knee?

    Yes, water has got in...but that is secondary; water does not produce cracks.

  26. #26
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    Default Re: Cold Molded Hull Cracks?

    The cracks in the OP ore on the bottom of the boat ~12" forward from the transom on the starboard side and roughly halfway between centerline and turn of the bilge. The cracks in post #11 are roughly 6' forward from the transom on the port topsides right under the rubrail.

    The boat is supported on long bunks perhaps 18" either side of the keel - somewhat unevenly as shown by the gap between hull and bunk in the OP. It is not well supported under the keel. Neither of these areas is near the mast or chainplates - those are within 2' of the stem, roughly 6' away. I'll get actual measurements as soon as the weather permits.

  27. #27
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    Default Re: Cold Molded Hull Cracks?

    Quote Originally Posted by pandelume View Post

    Regarding damaged wood, am I right in thinking that discoloration does not necessarily mean rotten or damaged? If the wood is discolored but dry and hard is it safe to glass over? By which I mean I won't be promoting further damage under the glassed area?
    You're right, go for it.

  28. #28
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    Default Re: Cold Molded Hull Cracks?

    Cooperative weather yesterday, so a couple of photos:

    20190518_102022.jpg

    20190518_125704.jpg

    Looking closer, it seems that she has a whole series of hairline cracks right around the boat - they seem to be between the veneers nearly all within 6" or so of the rubrail. I tried taking pictures, but either they're to close to show the distribution or too far away to really show any cracks. The little cracks on the topsides don't seem to have any correlation to where the bunks are or any other obvious connection to other aspects of the boat. The rubrail has been sealed to the deck with a fillet of epoxy, like so:

    20190518_102106.jpg

    But the underside of the rail doesn't seem to have any sealing, as shown in this photo:

    20190518_102119.jpg

    These are showing the upper and lower sides of the same section of rail. So I think the diagnosis above about humidity/moisture causing the veneers to swell or contract causing these cracks is probably what's going on. Stripping the whole boat is not a practical option for me at this point - the fix needs to be broken into bite-sized pieces. I'm thinking maybe take off the rails and glass the top 6 or 8 inches of topsides and up over the deck join. That's not trivial, but it's probably something that can be done without spoiling the whole summer. I'm open to suggestions from the more experienced.

    I have ordered epoxy and some 1.5oz glass cloth, so things will be on hold until that arrives. In the meantime, I'll see what I can do about supporting the boat under her keel on the trailer.

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