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Hull thickness question


bigste

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Been looking at boats recently with a view to buying and something occurred to me which I don't have an obvious answer for.

When looking at hull thicknesses I see the common one is 10mm but there are others ranging from 6mm right up to 12mm or even 15mm. Sides are nearly all 6mm with very few being 6mm. Now somebody will tell me I'm wrong in thinking that the most wearable part is the waterline. If that's the case why is the side the thinnest part.

From what I've found out over the years, a boat is replated usually because the sides are badly rusted along with the counter.

I would think a 10mm base is a good selling point against a 6mm base, but is it a false sense of security. Surely it's not the base we should be bothered about, more like the sides which are nearly all 6mm.

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If the sides and roof were too heavy, the boat would be in danger of toppling.

That. Also the bottom plate can be subject to a lot of wear, so thicker is better, with the advantage of needing less ballast adding.

There is some variation from make to make. Unusually my boat has 6mm cabin sides, but less internal steel strengthening which tends to even the weight out.

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There is some variation from make to make. Unusually my boat has 6mm cabin sides, but less internal steel strengthening which tends to even the weight out.

That is unusual. My boat plate spec is 5:5:6:10. They used 5mm for the roof rather than 4mm because the span is so wide.

Edited by blackrose
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In the 70s and 80s narrowboats were typically built with 6mm sides and bottom (with budget boats like Springers thinner). The tendency to increase bottom plate thickness to 8mm to 10mm to 12mm or more has been justified on the grounds that few paint the bottom (a pig of a job and anyway it gets worn off), so the extra thickness gives a reserve against corrosion, and secondly that it reduces the amount of ballast you need to provide.

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That is unusual. My boat plate spec is 5:5:6:10. They used 5mm for the roof rather than 4mm because the span is so wide.

It does seem to be unusual. One other builder used to do this it seems, but can't remember who now.

Edited by Guest
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That is unusual. My boat plate spec is 5:5:6:10. They used 5mm for the roof rather than 4mm because the span is so wide.

 

Built in Australia?

 

I believe the 'normal' specification is quoted from the bottom up.

 

ie. 10,6,5,5.

 

Mine (narrow) is 10,6,5,4.

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Whatever... I've seen it written both ways. As long as you understood that's fine.

So have I: one way by you, and the other way by absolutely everyone else. Why do the awkward so-and-so's insist on marching out of step?

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Ihave had 6,10 and 15 mil bottoms. I have had hull thicknesses of 5,6 and 8. All were good boats non were ever plated even the 6 mil bottom 30 year old boat I owned.

The heavy bottom makes for a low s.o.g and less ballast but there is a load of inane crap talked about hull thicknesss. All are up to the job and as Blackrose says looking after it is more important than thickness although I bought a 6 mill bottom boat that had never been out of the water or blacked for 18 years and was 30 years old when I bought it and it was still all near 6mill. ( Colecraft ) that one as it happens.

 

Tim

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Mine is 8 5 4 4

on the last survey this summer he found 8 was down to 7.6 at the worst, the 5 was down to 4.7 at worse and this is a 20 year old boat, I believe it has nothing to do with thickness but more to do with looking after hull

Pretty damn good after 20 years I would think. May I ask if you have kept the bottom plate blacked?

Edited by Guest
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Mine is 8 5 4 4

on the last survey this summer he found 8 was down to 7.6 at the worst, the 5 was down to 4.7 at worse and this is a 20 year old boat, I believe it has nothing to do with thickness but more to do with looking after hull

Don't forget that the plate thickness will be subject to a plus for minus specification variation from the nominal, say 8mm thickness, so could in fact still be the original thickness, with no loss.

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Don't forget that the plate thickness will be subject to a plus for minus specification variation from the nominal, say 8mm thickness, so could in fact still be the original thickness, with no loss.

still not bad for 20 years and shows if you look after a boat it will last decades

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So have I: one way by you, and the other way by absolutely everyone else. Why do the awkward so-and-so's insist on marching out of step?

Except that since I've seen it written the other way several times then not "absolutely everyone else" is doing it right. Had you considered that it might just be a simple mistake rather than people intentionally tying to be awkward?

 

I've seen written both ways so I thought either was ok, but if matters to you that much my apologies.

 

In my opinion the awkward so-and-sos are the idiots who revel in any opportunity to pick up on the smallest error so they can rub people's noses in it. This forum is full of them. I guess it makes them feel good about themselves or something...

Edited by blackrose
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Don't forget that the plate thickness will be subject to a plus for minus specification variation from the nominal, say 8mm thickness, so could in fact still be the original thickness, with no loss.

5 thou or .125 mm is normal tolerance, any QM would get the sack for allowing anything out that far under. Unless it was supplied on the cheap anyway ;)

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