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  1. #1
    Join Date
    Sep 2015
    Location
    Southampton
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    473

    Default Double Diagonal Topside Seams

    The topic of open seams came up on another thread, I mentioned my issue on there but thought I'd best start a new thread so not to hijack the other one.

    I'm currently restoring a double diagonal motor boat, it's in the water at the moment and there are no issues with the seams below the waterline. The problem I have is with the topsides, the original calico layer has perished away meaning you can see daylight through the hull at the plank intersections, also it is allowing water to get in between the layers.

    Since she's already in the water there's not going to be any more take up (which is restricted by the copper bottom) however I can't fill the seams with anything hard like epoxy since there is still movement in the seams; in summer they open up, in winter some close completely and others close slightly.

    If I put something squidgy in in summer, it will squidge out in winter fine, but then come the following summer the planks will open back up and the gap will re-appear. If I put something like sika in in winter when the gaps are smallest, there's no risk of damage, but in summer when the planks want to open, no doubt the bond will fail and I'll be back to square one.

    Does anyone have any good suggestions or experience of what to do in this situation?
    Jouet Golif 'Aljonic'

  2. #2
    Join Date
    Nov 2002
    Location
    Colwell Bay
    Posts
    5,671

    Default Re: Double Diagonal Topside Seams

    I'd like to know more about your boat?

    Its an interesting question and I don;t know the answer, is it just a fact of life with that kind of boat?

    Mine is a hot moulded hull, so there's virtually no movement.

  3. #3
    Join Date
    Sep 2015
    Location
    Southampton
    Posts
    473

    Default Re: Double Diagonal Topside Seams

    Ex RAF air sea rescue, built in 1942 in Dartmouth. She's managed to avoid being turned into a houseboat but has been left for the better part of 20 years. The copper bottom has meant that everything is sound below the waterline, but fresh water ingress through the decks and topside planking is starting to cause issues.

    I've been hoping the application of salt and fungicide will stem the problems long enough for me to come up with a solution. I thought about over-moulding with strips of veneer, but not sure if that's a sensible idea or not as it would hide what would then be the middle layer.
    Jouet Golif 'Aljonic'

  4. #4
    Join Date
    Nov 2002
    Location
    Colwell Bay
    Posts
    5,671

    Default Re: Double Diagonal Topside Seams

    Ah yes, its rain water that gets them.

    Not many of the old military boats left now, when I was kid there was old SAR and MTB etc all over the Hamble, thankfully we have a good cross section in preservation.

  5. #5
    Join Date
    May 2001
    Location
    South Dorset/moored Poole/lay up Wareham
    Posts
    340

    Default Re: Double Diagonal Topside Seams

    I think the main problem will be that the many thousands of fastenings, probably at least 4 at each plank cross over will now be slack as the calico has rotted & caused the skin to be thinner than it was when originally fastened. Add the issue of the heads of the fastenings, probably copper rivets, having drawn into the timber somewhat & now the individual skins are now not tight to one another & moving around as the boat works making matters worse as the nails open up bigger holes in the planks. In the past the only way of attending to this was to strip off the outer skin & remove the rotted calico & then refasten using thousands of new fastenings. This work was usually funded by a preservation society & a lot of willing hands. Difficult problem to solve for the individual recreational owner. Either spend a fortune or very little, perhaps epoxy sheathing but that will almost certainly just stave off the inevitable end of the vessel in a few years making a professional restoration virtually impossible . Anything in between would likely be money thrown away.
    www.seasurveys.co.uk
    Surveying & Shipwright info on GRP, WOOD & so much more

  6. #6
    Join Date
    Sep 2015
    Location
    Southampton
    Posts
    473

    Default Re: Double Diagonal Topside Seams

    That's quite damning, I was hoping for better news!

    The planking still seems to be well fastened, but I'm not a surveyor. Is the situation you've described always the case in your experience or does it vary boat to boat?

    There was an article in PBO recently about MTB102, the planking of which is largely original and the pictures seemed to suggest they'd used something in the seams between the planks. I've tried to call the trust a couple of times to enquire about it but there's been no answer.
    Jouet Golif 'Aljonic'

  7. #7
    Join Date
    Oct 2014
    Posts
    367

    Default Re: Double Diagonal Topside Seams

    We used to have a double diagonal lifeboat. Originally dark blue. Painting it white (I know, I know) helped reduce movement. There really should be no movement in a D/D hull but reality several years later is a different matter.

    As someone has said, the correct approach is re-fastening and replacing calico though being a realist I am a great believer in any Sika type product that doesn't go hard...and some stay softer if overpainted.

  8. #8
    Join Date
    May 2001
    Location
    South Dorset/moored Poole/lay up Wareham
    Posts
    340

    Default Re: Double Diagonal Topside Seams

    Quote Originally Posted by PotatoNavigator View Post
    That's quite damning, I was hoping for better news!

    The planking still seems to be well fastened, but I'm not a surveyor. Is the situation you've described always the case in your experience or does it vary boat to boat?

    There was an article in PBO recently about MTB102, the planking of which is largely original and the pictures seemed to suggest they'd used something in the seams between the planks. I've tried to call the trust a couple of times to enquire about it but there's been no answer.
    It may be that if you have someone that can give an honest opinion after looking at the hull, the outcome might be better after all, not all hulls are the same and there might be a remedy within financial acceptability. My thoughts were that, at this time, there is no practical long term remedy that will reinstate the integrity of the planking that does not involve tightening or replacing the fastenings. The difficulty is that the calico has probably rotted and this, in wet contact with the internal faces of the planks ( mahogany?) may have caused freshwater decay to the surface which is not obvious at this time. My thoughts were that you could spend a vast amount trying to improve the situation which could be money thrown away if ultimately the fastenings, calico and planking could not be confirmed as sound for another few decades. Spend a little or a lot, but nothing in between. You could take a core sample here and there and see what the planking is like out of sight, just use a hole cutter, about 1.5" and see. A small hole such as that well above the waterline could be easily reinstated. At least then you might have a better idea of what might lie ahead. Epoxy saturation might be a possibility if you can flood the internal faces where the calico is, provide it is totally dry. Sorry about being pessimistic, just trying to be realistic.
    www.seasurveys.co.uk
    Surveying & Shipwright info on GRP, WOOD & so much more

  9. #9
    Join Date
    Oct 2014
    Posts
    367

    Default Re: Double Diagonal Topside Seams

    Quote Originally Posted by johnlilley View Post
    Epoxy saturation might be a possibility if you can flood the internal faces where the calico is, provide it is totally dry. Sorry about being pessimistic, just trying to be realistic.
    At the risk of hijacking the OP's thread I am pondering this at the moment. My challenge is delaminated top layer of ply on rolled ply decks on a small old dinghy. I was considering injecting epoxy into the plies of the ply and then strapping down until dry.

    My questions are:
    1) Can one thin epoxy to make it runnier and therefore creep and soak in? If so is acetone the thinner?

    2) If I were to drill holes and use a disposable syringe, which seems the obvious route, any suggestions as to needle diameter/bore?

    I suppose the OP could do something similar and then fasten through as it dries?

  10. #10
    Join Date
    Oct 2001
    Location
    Micheldever, hants
    Posts
    1,644

    Default Re: Double Diagonal Topside Seams

    i would have thought it best to consult somebody like West epoxy. I seem to recall we used acetone as a thinners at my place of work but I could be wrong.

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