On a wood (carvel planked) boat, i think the 'correct' method is to fill
the hole with a wood plug and back it up with duplicate of the boat's other
butt blocks, through-bolted. Typically, this would be the width of the
plank, as long as a frame space and of somewhat greater thickness than
planking stock.
Remember that transducer backup and fairing blocks were held in place by
the transducer itself. Without the transducer as a fastening, you need to
find another way to hold the works together. Just plugging the hole won't
do.

"David Flew" wrote in message
...

Hi
Whilst I can see the reason for a full epoxy / glass patch, I was thinking
more of a similar job we did on a wooden boat. The old transducer was in
a
mounting block, so there was about 3" depth of hole once the transducer
was
removed. No way a wooden plug glued in place with epoxy / fibres was
going
anywhere. I'd not though about hull flexing. Just goes to show how hard
it
is to describe issues in words, let alone the appropriate fix!
David
wrote in message
oups.com...
Dave, Don't follow the plan of basilk or David of just putting a plug
in the hole.If the hull flexes and it pops out or you scrape a rock and
it pops out or it just pops out from water pressure, most likely you'll
sink with your bilge pump pumping. Both sides of the hole need to be
ground back in a taper and resin and glass fabric on both sides used to
seal the hole. Follow the directions on the site Jim C. supplied, the
third category, High Risk, example 8, and you will be doing it right.
If you know what you're doing and have the tools and materials you
could do it in an hour or two. Sam