KLC Lewis wrote:

Is it ever possible to get a primary bond between polyester resin and
epoxy? I don't know, but I've been told "no" by so many people over
the years that I tend to act as if I believe it.

"They" always told me to use epoxy on old polyester because it would be
stronger than new polyester to old. Maybe not a primary bond but strong. I
remember gazing at my navel over a transducer through hull backing block
that wouldn't have much mechanical connection because the fitting was the
flush type with very little shoulder. I wanted to use 5200 because of the
difficulty in fitting a block tightly and working with epoxy at arm's length
in a small space. According to the published tensile strength numbers, the
6" x 6" block would lift the boat. Now, I wouldn't stand under it if I
tried it but it seemed like plenty of strength for the job to me.

Some perspective on strength may be in order. If "Flying Pig" had been a
classic wooden boat, the total tensile strength of her hull would have been
the area of the frames or about the same as less than 3/8 inch of wood. The
static caulking and swelling pressure would already load up these structural
members significantly. Her bulkheads would have probably landed on a frames
and had two screws in each plank, maybe 80 screws in all and each close to
the end of the plank they held. Boats of this construction have weathered
many storms and circumnavigations. Most of them had some rot somewhere by
the time they were really tested.

It's true that, if FP had been a wooden boat, S&L probably would have been
standing in the water long before the chopper arrived. It would also be
nice if the restored boat was as strong or stonger then when built.
However, there is also the question of how strong it really needs to be.
Stronger is always bettter but, if that was the only consideration, we would
all be sailing steel boats.

If the best tabbing job that can be done without stripping the boat fails
down the road, it's highly unlikely the boat would sink, even in a major
storm. They might have to ease off on the sails and limp a bit but the
worst probable case isn't that dire. The most likely failure mode would be
for the localized high stress areas to start to open up. The big gun
repairs could then be concentrated on those in a year or two.

Remember, this boat was pounding on coral with all these structural members
loose and she still came off watertight.

--
Roger Long