Double Diagonal Topside Seams

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PotatoNavigator

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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?
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
PotatoNavigator said:
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.
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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.
 
johnlilley said:
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.
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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?
 
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.
 
Thanks, you have encouraged me to answer my own question with the able support of the interweb.

West Systems suggest that thinning with a solvent is bad (or at least ill advised) practice. Heat is recommended. Either heating the epoxy (before mixing) or heating the item to be epoxied...or both

When it comes to syringes others say that any needle is pretty hopeless and using the syringe itself is best, maybe countersinking the entry hole to make a good fit and allowing for higher injection pressure.

This could be fun!
 
If you heat époxy to thin it, use the slowest hardener available. Heating the wood is better. But, one has to say, these double diagonal hulls were not expected to last more than a few years. So any left require some ingenuity, or a lot of money.
In one case I know of, the damaged planks were replaced with sika type joint, then the whole lower hull skinned with époxy/glass. Purists would shudder, but the boat had been out of the water for many years in the dry and the planks were shrunk and cupped. Replacing the whole lot was beyond the skills and budget. Plus, it was not a big project, like a ASR boat.
 
Hang on, if I'm correct the OP's undercarriage is OK, it's the topsides. If this were some piece of historic memorabilia a solution wouyld be found. If the wood itself is OK then trial and error should come up with something. There was the infamous silicon injection DPC into my cottage which I undertook because the bank manager giving me the loan was also helping the injectiion co with their startup (complete waste). There are products which are designed to creep into small places, and maybe remain flexible.

Tooth repair for example, ususally wet: https://en.wikipedia.org/wiki/Dental_composite
 
fisherman said:
Hang on, if I'm correct the OP's undercarriage is OK, it's the topsides. If this were some piece of historic memorabilia a solution wouyld be found. If the wood itself is OK then trial and error should come up with something. There was the infamous silicon injection DPC into my cottage which I undertook because the bank manager giving me the loan was also helping the injectiion co with their startup (complete waste). There are products which are designed to creep into small places, and maybe remain flexible.

Tooth repair for example, ususally wet: https://en.wikipedia.org/wiki/Dental_composite
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You are correct, below the waterline everything is sound so far as I can tell, everywhere I've jabbed with a screwdriver has been rock hard, this in mind is it fair to assume the fixings will be equally sound? I'm not sure what the lifespan of copper fixings is. Johnlilly, to what extend is it possible to survey the bottom of a boat that's copper sheathed?

What I've been trying to avoid is the considerable expense of a lift out and storage ashore, money which I would prefer to spend on materials. If it comes to it, it would be financially viable (just!) to remove and refasten the outer layer of planking, replacing where necessary and re-bedding on a modern alternative to calico and white lead.

Someone will probably say if this is an option then it's the obvious solution, however I don't know what the negative effects might be on the bottom planking from spending a long period of time ashore. As far as I know the boat has never spent any considerable time ashore since its refit in the 50s.
 
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PotatoNavigator said:
You are correct, below the waterline everything is sound so far as I can tell, everywhere I've jabbed with a screwdriver has been rock hard, this in mind is it fair to assume the fixings will be equally sound? I'm not sure what the lifespan of copper fixings is. Johnlilly, to what extend is it possible to survey the bottom of a boat that's copper sheathed?

What I've been trying to avoid is the considerable expense of a lift out and storage ashore, money which I would prefer to spend on materials. If it comes to it, it would be financially viable (just!) to remove and refasten the outer layer of planking, replacing where necessary and re-bedding on a modern alternative to calico and white lead.

Someone will probably say if this is an option then it's the obvious solution, however I don't know what the negative effects might be on the bottom planking from spending a long period of time ashore. As far as I know the boat has never spent any considerable time ashore since its refit in the 50s.
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Have you been able to access any underwater planking for testing directly or is it all copper sheathed below the waterline.
In answer to you question referring to inspecting through copper sheathing the the quick answer is no, you cannot realistically assess the planking condition below the waterline where it is copper sheathed.
Copper fastenings have a long life....in most circumstances. What can happen is that the internal rove ( the washer over the nail end) becomes very thin and easily comes off or disintegrates and does not hold the nail tight and in effect the rivet fails. Check these, if you can lever it off easily with a screwdriver then that would not be a good sign.
It might be possible to remove the external skin to access the calico and replace but the removal of hundreds and hundreds of fastenings is not to be taken lightly. The likelihood is that a percentage of the external and perhaps internal skin planking would be damaged as it is probably only 12mm or less thick. If you do not count you own labour and time then possibly it could be possible with a limited budget but it would be an endless task and with the inherent risk that one might just give up half way through making the vessel into a liability and unsaleable. Bear in mind that in order to remove just one plank you would have to access many dozens of fastenings internally and you must be able to access every single fastening which is sometimes near impossible on a completed hull with joinery , engines, etc.. I would strongly advise to investigate a bit more before spending a single penny.
 
There are water based epoxies, which would not require the planking interface to be totally dry, might be an idea. to inject that.
 
I think its a do or die situation.

Do nothing and its eventually a one way street.

When Phil Clapburn rebuilt MGB81/HSL102 and the little one, was it 1502, I think he inverted them all, removed the entire outer planking, cleaned off, epoxied new outer planking on with fastenings of course, then epoxy cloth sheathed them. they seem to be standing up well. (I might be able to put you in touch with Phil)

Its a tricky construction that's for sure.

The Americans use a product by 3M called 5200 on the bottoms of their Chris Craft although I have not seen it applied here in the uk much., although a chum in Hythe did it to an American lake boat, I've not seen it.

Ashcroft boats must be even worse with a 3rd outer layer running fore and aft.

I've only got 9 layers to worry about.

i'd love to see a few photos.

Ben
 
johnlilley said:
Copper fastenings have a long life....in most circumstances. What can happen is that the internal rove ( the washer over the nail end) becomes very thin and easily comes off or disintegrates and does not hold the nail tight and in effect the rivet fails. Check these, if you can lever it off easily with a screwdriver then that would not be a good sign.
It might be possible to remove the external skin to access the calico and replace but the removal of hundreds and hundreds of fastenings is not to be taken lightly.
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So I popped down to the boat after work to look at some of the bottom fastenings, all of the roves I looked at seemed to be in good condition and couldn't be moved at all with a screwdriver

There's not a lot of interior left inside the boat other than bulkheads so I have pretty good access to the fastenings on the inside, including in the engine room since there's a couple of feet between each engine and the planking.

burgundyben said:
I think its a do or die situation.

Do nothing and its eventually a one way street.

When Phil Clapburn rebuilt MGB81/HSL102 and the little one, was it 1502, I think he inverted them all, removed the entire outer planking, cleaned off, epoxied new outer planking on with fastenings of course, then epoxy cloth sheathed them. they seem to be standing up well. (I might be able to put you in touch with Phil)

Its a tricky construction that's for sure.

The Americans use a product by 3M called 5200 on the bottoms of their Chris Craft although I have not seen it applied here in the uk much., although a chum in Hythe did it to an American lake boat, I've not seen it.

Ashcroft boats must be even worse with a 3rd outer layer running fore and aft.

I've only got 9 layers to worry about.

i'd love to see a few photos.

Ben
Click to expand...

I think you're right about it being a do or die situation. The opinions on this thread are bringing me round to the idea it might be better to do something drastic now and get the boat sorted for a decent period of time than keep fighting a losing battle.

I'm confident the bottom is sound, so unless I discover something awful I intend to leave it well alone under its copper.

I'm familiar with the restoration of HSL102 but it's not a route I'd like to go down if I can help it.

Visitors are always welcome Ben if you want to come and have a look, I'm interested in gleaning other peoples knowledge and suggestions.
 
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