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hi all, has anyone on the forum had any experience with replating a nb that has been sprayfoamed as insulation,if the replating were to come up to the waterline would all of the sprayfoam need to be removed,thanks in advance

 

i mean overplating,replating the sprayfoam would come off with the old plate,sorry to not make this clear

Edited by dreadnought
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hi all, has anyone on the forum had any experience with replating a nb that has been sprayfoamed as insulation,if the replating were to come up to the waterline would all of the sprayfoam need to be removed,thanks in advance

 

Do you mean 'replating' (not common), or 'overplating' (more common) ?

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I once had a narrowboat over-plated and had polystyrene (think that is what it was) sheets as insulation. It did not have to be removed but I do know the welders also took fire precautions. A subsequent survey passed the welding and the boat went on for some years and I then sold her. Have no experience with spray foam though, sorry.

Edited by Traveller
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hi all, has anyone on the forum had any experience with replating a nb that has been sprayfoamed as insulation,if the replating were to come up to the waterline would all of the sprayfoam need to be removed,thanks in advance

 

i mean overplating,replating the sprayfoam would come off with the old plate,sorry to not make this clear

 

 

Well you can be certain the hull will glow bright red on the inside wherever the welding takes place.

 

Whether this ignites the sprayfoam I'd say depends on exactly what foam was used. Try cutting a bit out and playing a blowlamp on it to assess the flammability. Some may be flame retardant. Possibly.

 

Many years ago a hull builder told me spray foaming was building in problems for the future, as and when the sprayfoamed boats need overplating....

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Being paneled in not much in the way of oxygen would be present. The polystyrene would probably roast a bit and go out, not burst into flames.

 

 

But the OP was asking about sprayfoam. Is sprayfoam the same material as polystyrene then?

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I have over plated with both spray foam and polystyrene without removing it it is not the same product and polystyrene can combust spray foam usually is fire retardant but will smoulder and stink and also make a mess It is in the way the boat is welded up that makes it possible to do this

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I have over plated with both spray foam and polystyrene without removing it it is not the same product and polystyrene can combust spray foam usually is fire retardant but will smoulder and stink and also make a mess It is in the way the boat is welded up that makes it possible to do this

It's that word "usually" that would worry me. There is definitely a sense of relief whenever I ask for welding to be done our boats, neither of which have sprayfoam or polystyrene insulation.

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What I can say is that "Flamingo", (as bought), largely used polystyrene slab, (which we are slowly replacing with Rockwool).

Taking it down, where welding has gone on with it in situ, there is little evidence of fire, but in m any places it has melted down to less than a third of its original thickness, and, as such I doubt it any longer provides anything like the same degree of intended insulation.

 

I have no experience of spray foam, but I would not be surprised if its effectiveness was reduced by welding to the hull to which it is attached.

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When we weld we use a staggered process the only area of concern regarding insulation is the top weld above the waterline we only weld in low amps which is sufficient in terms of joining the old steel to the new and doesn't produce excess transference of heat to the inside of the boat we also move regularly in the process and cool the area further to this there is a second person on duty inside the boat

  • Greenie 1
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The boat on the left has undergone refooting (a form of replating), and shows the effect of the heat from cutting away the old metal. I would still be tempted to test the spray foam on your craft as I doubt all are as fire retardant as this.

post-23974-0-51971300-1486051189_thumb.jpg

Edited by BWM
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We don't cut away the metal as in replacing it as this would require a complete strip out and refit of the interior of the boat often making it uneconomical

We over plate leaving the existing steel in situ

This is what we are having to do with our butty. Originally we just wanted the back cabin to be re-skinned. However, it soon became evident that the back end was in such a poor state that radical treatment was needed. In parts there was overplating of the overplating! There was no alternative but to strip everything off and start again.

The butty is at present is being restored at Stockton Dry Dock (Warwickshire Flyboat).

We're hoping that the boat will be ready for Braunston, complete with a new back cabin which will be fitted out by Reg Thompson and decorated and lettered by Dave Moore.

 

post-5123-0-51777000-1486060583_thumb.jpg

Before work began

 

post-5123-0-56718400-1486060613_thumb.jpg

Back cabin has been removed . . .

 

post-5123-0-79440700-1486060768_thumb.jpg

. . . and the stern end has been replated.

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But the OP was asking about sprayfoam. Is sprayfoam the same material as polystyrene then?

No, sprayfoam is polyurethane.

 

I've had some welding done on the roof over sprayfoam. It did catch and I set off a powder fire extinguisher. I was hoovering up for days. So I wouldn't fancy doing it with paneling over the top without any access.

 

Any fire retardant materials are just that. Fire retardant doesn't mean fire proof - it just means you have a longer time compared to the standard grade of material before they will ignite.

Edited by blackrose
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We don't cut away the metal as in replacing it as this would require a complete strip out and refit of the interior of the boat often making it uneconomical

We over plate leaving the existing steel in situ

I added the photo showing replating only as an example of the effect from the heat of cutting/welding, most modern craft are overplated for the reasons you stated.

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Well I'd strip the internals ,cut out all the rot. And fit new plates butted up to existing edges,with chamfers .it's the only proper way to do it,

But same old story it's all about cost and compromises

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Well I'd strip the internals ,cut out all the rot. And fit new plates butted up to existing edges,with chamfers .it's the only proper way to do it,

But same old story it's all about cost and compromises

But could you explain technically why it is the 'proper' way to do it?

 

The original question has been answered by a person who is an authority on the actual subject of the question and it wasn't about whether they should overplate or replate. They will be fine.

 

JP

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All I'm saying about over plating is that all the crap underneath gradually swells and starts to push the patch off making it bulge and rot the inner face of the patch .

And if the original metal was thick enough to fillet and plug weld a patch on , it wouldn't have needed a patch to start with ,and I think after

Serving. My time as a boilermaker plater , and lloyds coded welder in every method for the last 46 years I could maybe call myself

A bit of a authority on it as well . if I had a wooden roof truss full of dry rot I don't think I'd screw a bit of ply all around it ,and it's just the same thing for steel, once the rots in there is only one way to sort it

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All I'm saying about over plating is that all the crap underneath gradually swells and starts to push the patch off making it bulge and rot the inner face of the patch .

And if the original metal was thick enough to fillet and plug weld a patch on , it wouldn't have needed a patch to start with ,and I think after

Serving. My time as a boilermaker plater , and lloyds coded welder in every method for the last 46 years I could maybe call myself

A bit of a authority on it as well . if I had a wooden roof truss full of dry rot I don't think I'd screw a bit of ply all around it ,and it's just the same thing for steel, once the rots in there is only one way to sort it

You are right, I have just decided my merc CLK isnt worth the effort of repairing it, the dreaded rot is everywhere so its time to strip it sell the good bits and make tin cans of the rest

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You are right, I have just decided my merc CLK isnt worth the effort of repairing it, the dreaded rot is everywhere so its time to strip it sell the good bits and make tin cans of the rest

 

Ahh the dreaded rotten mercs........Is it from around 2000 ish perchance?

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All I'm saying about over plating is that all the crap underneath gradually swells and starts to push the patch off making it bulge and rot the inner face of the patch .

And if the original metal was thick enough to fillet and plug weld a patch on , it wouldn't have needed a patch to start with ,and I think after

Serving. My time as a boilermaker plater , and lloyds coded welder in every method for the last 46 years I could maybe call myself

A bit of a authority on it as well . if I had a wooden roof truss full of dry rot I don't think I'd screw a bit of ply all around it ,and it's just the same thing for steel, once the rots in there is only one way to sort it

What we don't know is the reason for and the extent of the plating. If it is due to pitting then there will be sufficient good parent metal. It's unlikely that a 6mm hull plate (assuming that's what it is) has corroded overall to any great extent in the lifespan of the average leisure boat. If any rust is treated and then sealed by the watertight welds that fix the new plate there shouldn't be any oxygen present to promote continued corrosion. Rot in wood is a fungus so isn't directly comparable but in both cases if the environment that promoted the problem in the first place isn't addressed then repair will be ineffective.

 

My boat effectively has a two-ply hull having been built in the sixties and totally overplated in the eighties. No problems yet.

 

JP

  • Greenie 1
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