Hole in the boat #1!!! Installing the side vent

This is probably the hardest part of the project. Boats are not meant to have any holes in them. Holes make boats sink. Get over it! Some say that a couple beers make this easier but I am not sure how straight it makes your holes!

You need to decide where to put your side dump hole. Check it out from both the outside for cosmetics and the inside for adequate spacing and access. If you already have a bilge outlet you can use it for reference.

I used a 1 inch stainless steel thru-hull side dump that I purchased at west marine. On the inside it has a hose barb for 1” ID hose. I had several size hole saws and I cut some test holes in a piece of wood to see what size was the tightest fit. The 1 ¼” hole saw was a very tight (too tight) fit but I chose it because the next size up was too big. After drilling the hole I used the rotary sander bit to make the hole just a smidge bigger. More on that later….

So once you have chosen your hole location and hole saw size, mask off the area with painters tape and mark it with a sharpie. Put on safety glasses and dust mask. Make sure you have adequate clearance on the inside for when the drill bit breaks through. Begin drilling with the hole saw in reverse and continue in reverse until well through the gel coat and into the fiberglass. This is to prevent the hole saw from binding or grabbing and cracking or spidering your gel coat. Don't press too hard. You can finish drilling the rest of the hull either in forward or reverse.

Once the hole is made use the rotary sander to radius (not sure if this is the correct term) the edge of the hole where the gel coat is. Essentially sand the gel coat edge back so it’s a small rounded edge with no sharp transition to prevent any future cracking/spidering of the gel coat. Try the thru hull fitting for size and rotary sand the hole if needed to get a good fit.

On the inside use a razor knife to trim the carpet well away from the hole to allow room for the nut to secure the fitting.

Once finished use a shop vac for clean up. Clean the new hole with acetone to prep for sealing with marine sealant. Coat the back edge of the thru-hull and some of the threads with the 3M 5200 marine sealant and seat in hole. On the inside put more sealant on to fill any gaps in the hole. Thread on the mounting nut and tighten. Wipe any excess sealant away and clean any remaining extra with acetone.

Masked and marked ready for drilling














The first hole with edges radiused














The hole from the inside with carpet cut back














The drill bit sander used to radius the edge and enlarge the hole














The thru-hull in place














From the inside with nut in place