John,
I have seen this type of construction many times by FG boat manufactures.
They practice this to save costs of course, knowing that the failure will
occur after any warrantee period. The best repair is often a case of
compromise and it differs from instance to instance. I am not where you are,
so it is difficult for me to be precise, but your object is to fish a
backing piece behind the glass inline with your fasteners. Consider cutting
an access hole to slip an aluminum bar in behind. It should be no less than
1/4" thick, because you will drill and then tap holes for the new machine
screws. The aluminum flat bar can be bent into a radius to facilitate
slipping the bar through your access hole. You should drill and tap one
1/4-20 hole in the center of the bend. Approximate a mating hole in the
remaining FG panel and drill that to .265" for screw clearance. Test that
you can reach this tapped hole with a temporary, very long screw. Adjust the
bar size or access hole if necessary. Don't be concerned about the access
hole, because you have to repair the FG anyway. Apply 3M 5200 adhesive on to
the aluminum flat bar and install as in the test. Align with the intended
fastener line and wind up the temporary screw. This will flatten the bar and
compress the adhesive to the back of the remaining FG. Repeat this as many
times as necessary to back the entire length of the fastener line. Next,
repair the access hole(s) with new FG and wait 72 hrs for the 5200 to set.
The FG and aluminum has different expansion rates, so the adhesive must be
strong, yet flexible. 3M 5200 is ideal for this application. Temporarily
install the new seat and drill the new screw holes to the correct 1/4-20 tap
size, #7, through the seat, FG and backing bar. Remove the seat and tap the
new holes. You may consider doing this last step in increments, because of
seat distortion under fastener load. You should use 316 stainless machine
screws installed with Copper Ease or equivalent anti-seize paste. This will
allow easy removal at a later date without concern of dissimilar metal
corrosion. Do not forget to use large SS flat washers or a mating aluminum
bar on the seat side, as the problem at the seat is the same. This will
spread the seat load across the entire length of the seat and mating FG.
Good Luck,
Steve
"John" wrote in message
...

The simple rule is NEVER use screws in FG. They will always fail.
Fastener
load must be distributed with some kind of backing.

That would make good sense if it were possible. The boat was built with
no
backing, and there is no access to the inside now.
Any suggestions?

I could possibly move the thing the ropes from the jib go through out
about
6 inches from the seat to the gunnels, where it can be bolted on. That
would take stress off the seat, but would change the geometry of the jib
somewhat.
Would that make sense, or would it ruin the boat?