Tips for boring out 3/4" drain thru-hull to fit a 1" thru-hull

[mnpracing]

Well I did it tonight. I was tinkering in the garage and was looking at the drain thru-hull on the port side and was thinking about how to bore that hole out. I used Maxpower220's advice and put a cork in the hole, which was about a 1-1/4" hole. I needed 1-3/8" to fit the 1" thru-hull, so really not much, just a 1/16th around the whole hole.....

I cut the stopper so that only about 1/4" stuck out of the hole, then started the hole saw (a carbide type with abrasive teeth, vs the cutting teeth) by hand. It fit snugly over the stopper so I twisted it a bit more until it met with the gelcoat. While holding a beer in one hand I just turned the hole saw by hand until I was through the gelcoat. I kept turning by hand until I was probably 1/16th into the fiberglass. Then I pulled out the hole saw and the stopper, and used sandpaper to chamfer the edges of the gelcoat. Then I reinserted the stopper, and put the hole saw in my cordless drill, and drilled very slowly until I went through. I was surprised at how thin the fiberglass was, only about 1/4". The gelcoat was about 1-1.5mm thick. Then I trimmed the carpet fibers back and that was it. Here's some pics: