I don't think you will know if it is a success for some time. What you
have done is made an educated guess that it will bond good enough for
something on display.

the oars were left out in a rainstorm and were bounced around on a trailer
(the roads are awful around here) before I gave them back to the boss who
pronounced them perfect and upped what he was paying per oar by 50p. When
these things are painted and nailed to a pub wall the bond is going to be
more than enough.

Nothing wrong with that and it sound like you
would not make the same decision if the use was marine

If I had some very cheap oars that I didn't mind bashing around I would, but
the oars I repaired could not be used for their designed purpose simply
because the filler is soft (designed for easy sanding) and it would be
ground off far too easily. No, I wouldn't trust a polyester-over-epoxy bond
in anything that had to take any kind of abuse. Something that is static
with a reasonable key? yes.

After seeing the mess that my dad's boat is becoming I have strong
reservations about using polyester in a marine environment period. It looks
as if water has been able to permeate the polyester/glass covered wood, but
it has been held there whereas in the surrounding varnish only wood, the
water seems to have been able to escape appearing to do less damage. I need
to tear into much of the keel and hog to shift rot and the wood I remove is
going to be replaced by epoxy, but I think that boat is well and truly on
it's way out after only perhaps 20 years, mostly through poor maintenance
(if I'd known 5 years ago what I know now it'd be a much different story...
but I'd also have been 13). Polyester did the job when there was nothing
better, and in the lamination of large amount of fibreglass may still be the
material of choice, but better materials do exist for this application now,
and at reasonable prices.

Al