Hole in the boat #2.... Installing the thru-hull scupper

You need to decide where to put your bottom thru-hull scooper. Check it out from both the outside for cosmetics and the inside for adequate spacing and access. The brass fitting on the outside is rather large. Make sure it is located where it will have access to turbulent free water to prevent any air bubbles from entering the ballast system. You also do not want it to interfere with water flow to your speed wheel, engine water intake, or cause turbulence under the depth finder.

I used a 1 ¼” bronze thru-hull scupper/strainer that I purchased at west marine. The hole saw that gave the best fit was a 1 5/8” size. So once you have chosen your hole location, mask off the area with painters tape and mark it with a sharpie. Put on safety glasses and dust mask and 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. Drill through the hull. 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 scupper in for size and for a flush fit. Use the rotary sander if necessary to custom fit.

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. Use the ½” long size 8 stainless steel screws to mount the strainer edges (drill pilot hole first but don’t go thru the hull). I also put some sealant in the screw holes even though they do not go all the way through. Wipe up any excess sealant. Clean with acetone. On the inside put more sealant on to fill any gaps in the hole. Thread on the mounting nut and tighten. I left all the extra sealant around the inside nut to make sure I had a good waterproof seal since it is below water line. Let it cure overnight before next step.

Prepped for drilling with a black dot as my center mark















This is one big hole. It would sink the boat in no time at all















The hole from the inside (left side of picture)















Sealant on the surface to be mounted (this is way too much BTW)















The scupper in place from the outside (still needs a little more clean up)















From the inside with extra sealant and nut in place