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Bruce[_4_]

On Sat, 27 Mar 2010 10:07:40 +0100, (Martin
Schöön) wrote:

Bruce writes:

For whatever reason the owner, or perhaps the surveyor, cut cores out
of the hull and had them tested. The cores tested at 90-something
percent of the calculated original strength of the hull material.

I find it highly unlikely they could calculate the original strength
with a 10% inaccuracy. The materials used were not characterized that
well and the variation in the lamination process is much bigger. I
have been told by a senior structural engineering consultant that
the uncertainty in fatigue life for the materials we know best--
structural steels -- is roughly 6%. Composites, even aerospace
qualities, are much, much harder to get good data on.

I am not sure whether they had sufficient data to do accurate strength
calculations although I had a book written back in he very early days
of fiberglass boat building by someone who was described as an expert,
that did list tensile strengths for various boat building materials
and certainly there would have been tests made before publishing such
a table.

Having said that, certainly there is a variance in strength of a
fiberglass structure that varies with all kind of things - chemical
makeup of the actual resin used, hardener/catalysis mix, amount of
glass and resin in the structure and so on. I assume that why they
said calculated strength.

There was no mention of the boat's history or how much time it had
spent in the water, and in England many boats are hauled out for part
of each year, so the testing was hardly a comprehensive study but, as
the magazine wrote, it did show that fiberglass did not deteriorate
greatly with age.

This is pure nonsense. Fiberglass laminates have limited fatigue life as
do all materials.

I didn't say that it didn't deteriorate with age, I said it didn't
deteriorate GREATLY with age.

This boat has lived a pampered life relative to its scantlings.

/Martin
http://hem.bredband.net/b262106/
Cheers,

Bruce