You should compare modern GRP to boats made in
the 1960's through the early 1970's. Those hulls will
last 100 years or longer. They will certainly outlive you.

There is not enough data on newer hulls. However,
as long as you patch the cracks they should last just
as long--assuming you make it back to a travel lift
in time.

Although an argument could be made that flexing absorbs
energy, however, I find the concept disquieting.

Still, in either case, failures will occur due to repetitive
stresses. A solid hull in general will last longer than one
that will oil can. BTW, the SCRIMP boats seem
particularly strong.

I hope you are not thinking of taking that day sailor
offshore! Before you do that you should hitch a ride
a few trips to 1) see if you like it, 2) see if you can
handle the puking.

Finally, you need to stop cross posting if you want
answers in here.

"Adrian Smith" wrote
How long should a modern GRP hull lasts as compared to one made 10 years
ago?

And how old is considered too old when taking a boat offshore into
potential rough conditions?