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Peter on the puncture resistance of plywood

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The background to this was the discussion that started on the PDRacer.com forum when we said we were going for 4mm plywood.

There was much comment to suggest that we were going much too light - but we (more or less) knew what we were doing - most small Australian racing craft are built of 4mm and in general are much more highly stressed than the PD Racer.

Typical plywood thicknesses for the American boats seemed to be in the 8 to 12mm range.

One of the forum members worked out a simple but quite accurate method of testing the puncture resistance of ply and produced a table of results.

We could see that our 4mm ply was less puncture resistant - but how much would be enough?

The following is Peter's response as to how puncture resistant ply really needs to be.



I agree that the test is indeed interesting, and to an extent informative, but I don't know
how to use the information derived in a logical way.

Do the results mean that cardboard would be an adequate boat building material?  In terms of puncture resistance, probably....what is the standard required?

I think it's interesting, but not valid, that a comparison was made after a collision with another boat.   If we have a crash in our cars we expect damage, why should this not be the case with boats?  We don't even expect to drive them home.   It is important to have multiple bouyancy chambers in our boats to ensure we can get home if they are damaged.

If we take this to a ridiculous extreme, how many times more puncture resistant is 1" ply??

A surfboard, with it's light glass over foam construction would probably be right down there with cardboard in this test, yet millions of them are used every day very satisfactorily.   Even when completely lost and washed against rocks, because of their light weight, the impact is often not severe enough to puncture the skin.

I am curious, has anyone ever seen a boat punctured through normal use other than by collision with another craft, or on a reef, and if so how?

Please accept my comments in the interest of debate, not as a criticism of the
testing!

Regards,

P




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