Re-Locating the Speedo Impeller
I relocated the speedo impeller from the forward dinette seat locker to the v-berth locker. First I made a fiberglass backing plate with 6 layers of mat and West System epoxy. I sanded the inside surface of the hull to remove paint and provide a rougher surface for the epoxy to bond to. I drilled through the whole thing for the speedo impeller mounting. The thru-hull is a bronze fitting made to mount flush with the hull. I drilled a pilot hole from the inside to get proper position in the middle of the backing and drilled the rest from the outside. I started with a hole saw the same diameter as the flange on the thru-hull. I cut in about 1/16" with this. I switched to a hole saw the same diameter as the shoulder of the bronze fitting and cut in about 1/4". I switched to a hole saw just larger then the threaded part of the thru-hull and cut all the way through the hull and backing plate. The hull here is about 1/2" thick and the backing of 6 layers of mat is about another 1/4".
After I cut the holes with the hole saw I shaped it to receive the thru-hull flush with the deck. I used a Dremel tool with a sanding drum attachment. This is a VERY effective tool for this purpose. In a few careful minutes I had the thru-hull fitting a bit deeper then flush. I mixed some epoxy with fairing additive. I applied it to the outside of the thru-hull and to the inside of the hole in the hull. I inserted the thru-hull and put a block of wood covered with wax paper against it to hold it flush with the hull. There was a little wiggle room for the thru-hull. I held the board up on the hull with a spring loaded curtain rod. From the inside I filled around the thru-hull with more epoxy using a syringe. I worked the thru-hull around to better spread the epoxy. I added silica to thicken the epoxy and topped off the hole around the fitting. I thickened it to keep it form running out on the slightly slanted surface.
The finished mounting required a bit of epoxy on the outside to even it up with the hull and some bottom paint.