KLC Lewis wrote:
Well, there's flexing and there's flexing.

Agreed.


.... Essie is built exceptionally
stout for a boat of her size, having been built back in '63 before
scantlings for fiberglass boats had been developed.

I've heard this a lot, but it's not 100% accurate. The Navy
was very interested in fiberglass for it's small boats
(gigs, whaleboats, utility boats, etc etc, which had been
previously built out of wood). In the early 1950s they paid
for, and published, a large scale engineering study of
fiberglass including how well it stood up to UV. Lots of
early boat builders used this reference.


But a boat on the hard is unlikely to be supported the same way as the water
holds her.

Agreed again. The cradle or jackstands should be positioned
to support the internal structural members, like bulkheads,
directly. And fiberglass will exhibit 'creep' under
consistent heavy load for a long time. But it won't creep if
it's not loaded past the point of measurable deflection.



.... The flexing
we are talking about isn't "oilcanning" from scantlings that push the lower
limit.


Actually, oilcanning is annoying but not particularly bad
for fiberglass. FG can withstand at least an order of
magnitude more cycles of flexing than steel before
fatiguing, in this respect it's far superior to metal.

If given a choice between a hull that had oilcanning in some
panels (for example, the big almost-flat section in the bows
of many boats) and one that flexed over it's whole length
from rig loads, I'd pick oilcanning. But it would be a lot
better to have neither.

Fresh Breezes- Doug King