I like this approach too. One variation on the theme has to do with filling
that void before glassing it over.
I had to replace an old knot meter. The new meter demanded a hole that was a
tiny bit larger which meant drilling out the thru hull by an additional and
tiny 1/8 ".
I removed the knot meter, drove a wooden bung into the hole from the outside
and marked the bung with felt tip at the surface of the hull. I then removed
the bung, shortened the bung by cutting it on the line and then marked
center with an "X" so it showed when I drove it back in the hole. Then I set
the proper hole drill in my drill, found center and started boring through.
In a few minutes I had cut into the bung and then into fiberglass and had a
perfect thru hull hole increased evenly by 1/8".
For this job, one could drill out the appropriate sized fiberglass plug in a
piece of hull (any repair yard scrap will do) and fill the unwanted hole
with that new plug. Glass it over and never know you had a thru hull.

"Robert or Karen Swarts" wrote in message
...
Grind a recess in the hull around the hole to be plugged on both the
inside and outside of the hull. Using epoxy (not polyester) resin, place a
layer of glass cloth around the outside or inside. Fill the hole itself
with resin-saturated glass fibers. Place another layer of glass cloth on
top of the patch. If needed, apply more layers of glass. Finish the
outside with a slurry of epoxy and glass spheres or other filler of your
choice. Sand it smooth, barrier cote, and paint. Oh, do this when the
outside temperature is above 50 degrees.

BS
"Roger Long" wrote in message
...
Can anyone point me to some good on-line info on plugging old through
hull holes in a fiberglass hull?

Any other advice appreciated. The yard wants 6% of what I paid for the
boat just to plug one and put a new backing block in another. I hate
working with glass but it looks like I'll be doing this myself.

--

Roger Long