Originally Posted by headdamage
What would be the best type of drill bit for enlarging an existing hole in the transom of my RIB? The boat is a Zodiac Hurricane 440 so fiberglass with wood core. Right now I have two hull drains that are about 3/4" dia and are unlined so water can to the wood. I want to enlarge these and seal them with new 1" hull drains.
Drill it oversize with a hole saw. You can fill the existing hole (flush) with a bit of wood to facilitate the hole saw drill bit when drilling.
Then fill the oversize hole with fibreglass.
When dry drill the correct size through the fibreglass with another hole saw.
This process will ensure that the wood core is properly protected.
This video may also be of help