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Marine plywood thickness

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stockton
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Marine plywood thickness

#322360

Postby stockton » June 28th, 2020, 7:39 pm

I am trying to replace the floorboards of a 30 year old Avon inflatable. The boards appear to be made of plywood which is about 11mm thick, which does not seem to be a standard imperial or metric dimension. Could anyone explain what thickness plywood I should be trying to purchase ?

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Re: Marine plywood thickness

#322364

Postby Breelander » June 28th, 2020, 7:49 pm

stockton wrote:...plywood which is about 11mm thick, which does not seem to be a standard imperial or metric dimension....


12mm seems to be a standard thickness, for example here....

http://www.chilterntimber.co.uk/product ... thickness/

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Re: Marine plywood thickness

#322377

Postby 88V8 » June 28th, 2020, 8:47 pm

Maybe it was 5/8" and it's swollen in the damp.

Is it crucial to match the thickness?

V8

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Re: Marine plywood thickness

#322383

Postby dspp » June 28th, 2020, 9:16 pm

stockton wrote:I am trying to replace the floorboards of a 30 year old Avon inflatable. The boards appear to be made of plywood which is about 11mm thick, which does not seem to be a standard imperial or metric dimension. Could anyone explain what thickness plywood I should be trying to purchase ?


Recently I had to do some marine GZ calcs and I used these as a data source for some of the hull build-up, they may help.

https://www.boulterplywood.com/MarinePlywood_4.htm

Frankly, for a little Avon, I don't think it matters.

regards, dspp

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Re: Marine plywood thickness

#322472

Postby stockton » June 29th, 2020, 9:36 am

It is a moderate sized Avon (340) and more or less essential to match the thickness. Hence my puzzlement.

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Re: Marine plywood thickness

#322482

Postby stockton » June 29th, 2020, 10:08 am

It would appear that plywood standards changed around 2014 and prior to that were manufactured to a 1972 standard but I cannot find the 1972 standards.

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Re: Marine plywood thickness

#322566

Postby todthedog » June 29th, 2020, 3:19 pm

All marine ply used to be made to imperial thickness and sizes and then rounded up or down to the nearest metric equivalent . That was when the UK made most of the plywood manufacturing kit. This could be the case if the original is old like me. :D

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Re: Marine plywood thickness

#322581

Postby jfgw » June 29th, 2020, 3:55 pm

todthedog wrote:All marine ply used to be made to imperial thickness and sizes and then rounded up or down to the nearest metric equivalent . That was when the UK made most of the plywood manufacturing kit. This could be the case if the original is old like me. :D

7/16" then?

Julian F. G. W.

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Re: Marine plywood thickness

#322847

Postby bionichamster » June 30th, 2020, 9:55 pm

You say that the old plywood is “about 11mm” which isn’t very precise given that what is available is 12mm thus only 1mm difference.

Is the old stuff slightly more or slightly less than 11mm? If it’s the former them maybe it is just a worn down 12mm?
Is 1mm really going to make a difference? If you think it is then Could you Sand down The New 12mm stuff slightly on one side prior to application of an appropriate sealer?

Bh

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Re: Marine plywood thickness

#322901

Postby redsturgeon » July 1st, 2020, 9:08 am

Do you mind being more specific as to why it is essential to match the thickness down to the last mm?

John

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Re: Marine plywood thickness

#323048

Postby stockton » July 1st, 2020, 6:19 pm

Two reasons which make a thicker plywood undesirable; one, the weight which is significant, and two, the boards fit into a space formed by the fabric at the back of the boat and the extra thickness will strain the fabric.
I am in some doubt as to whether a 9mm ply would be strong enough.

The reason for my original question was that if I can discover exactly what was originally used I might well be able to source an exact replacement but at the moment I am having difficulty understanding the original spec - 7/16 sounds most probable but then what surprises me is that 7/16 or 10 mm is such a useful thickness that it is not available on its own merits.

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Re: Marine plywood thickness

#323064

Postby bionichamster » July 1st, 2020, 7:34 pm

stockton wrote:Two reasons which make a thicker plywood undesirable; one, the weight which is significant, and two, the boards fit into a space formed by the fabric at the back of the boat and the extra thickness will strain the fabric.
I am in some doubt as to whether a 9mm ply


Could you sand a slight 1mm+ taper along the edges Of a 12mm board that the board is the correct width where it sits in The fabric but slightly thicker in the center?

Bh

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Re: Marine plywood thickness

#323069

Postby stockton » July 1st, 2020, 7:53 pm

bionichamster wrote:Could you sand a slight 1mm+ taper along the edges Of a 12mm board that the board is the correct width where it sits in The fabric but slightly thicker in the center?
Bh

That is what we have ended up doing. The weight difference remains inconvenient.

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Re: Marine plywood thickness

#323114

Postby dspp » July 1st, 2020, 11:03 pm

stockton wrote:
bionichamster wrote:Could you sand a slight 1mm+ taper along the edges Of a 12mm board that the board is the correct width where it sits in The fabric but slightly thicker in the center?
Bh

That is what we have ended up doing. The weight difference remains inconvenient.


That sounds like the newer ply is denser, i.e. better quality.

regards, dspp


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