Thanks, Bernie. I think we may have another case of my failing to say
what I'm thinking. One day I'll learn not to think too quickly at 3
AM! I must've been unduly eager to beat Judy to the answer. ;-)
I agree (I think) that FRP is not subject to work hardening, and thus
repeated flexure within reasonable limits will not necessarily lead to
failure. My first flirtation with mal de mer was after sailing upwind
for some time with my head stuck down under the berths, watching the
area of the hull just below the chine flex as we pounded. Ursa was
new, and the new resin smell made that a bad place to be breathing,
especially upside down and bounding around! Nonetheless, the flexing
did not appear sufficient to be worrisome
The concept I'm playing with is that a panel which oilcans under
routine loads is subject, under greater but not impossible loading, to
failure due to excess deflection. [Think of it as tearing, although I
believe it's still technically a tensile failure.] With intact
stiffeners, such excess deflection could not occur until the stiffener
or the stiffener/hull connection failed, switching the failure mode to
one requiring much greater loads.
[As an aside, this seems to be yet another area of difference among
model years. The post that started this described athwartships tubes
only. I have an entire network, fore/aft and athwartships, outlining
the exposed sole area and extending outwards to the chine. Solar Fry
says he has none.????] Regardless, my gut says the stiffeners are
needed. I don't understand why they may no longer be included. In any
case, if present, their adhesion to the hull panels should be complete
and strong or they won't be doing their job.
As always (guess I should put this disclaimer in my signature?), I may
be full of fecal matter wrt the analysis ... Mech 103 was a long time
ago! I do have one anecdotal contribution, namely the panic I felt
when Ursa Minor was thrust with great force against a large fender
when rafting with a larger boat. I was belowdecks preparing to arise
and set a record for getting up, out, and underway. The crackling
noises as the topsides flexed were extreme -- and extremely
frightening! I was shocked to find no _observable_ damage.
Regards,
Bill Combs
WWP 19 #439 (Aug 1987)
"Ursa Minor"
Fort Walton Beach FL
ttursine@gnt.net