Plugging bottom holes

Our very well-preserved 1972 Tartan 34.5 had two paddle wheel-type knot meters and two 2-inch thru-hull depth sounder transducers. All four were more than 30 years old and hopelessly out of date. The four thru-hull fittings were made of very durable plastic but required 2-inch tapered holes in the half-inch hull bottom. The thru-hulls were tapered inward, making the bottom seal areas slightly more than half an inch. Nevertheless, the age of the thru-hulls and the seals made us nervous. Occasionally one of the knot meters would dribble seawater from the end of the paddle-wheel fitting located inside the hull. I would carefully adjust it, hoping the O-ring would seal better and stop the leak. On one occasion I couldn’t stop the port knot meter leak. At anchor, Kathy went over the side, swam around under the boat and held our small toilet plunger over the port knot meter so I could remove the paddle wheel from inside the boat and replace the O-ring. The toilet plunger sealed the hole very effectively, and I was able to replace the O-ring. Kathy removed the toilet plunger; the leak had stopped. Kathy frequently reminds me of that trick.

Enough already! New chartplotters with GPS replace the need for thru-hull knot meters. Sure, we don’t know the current speed with GPS, but we’re not racing and most times we can estimate the current close enough. New depth sounders are much better than the old ones. We replaced both old depth sounder transducers with a forward-looking, dual-frequency sounder linked to our chartplotter. The amazing thing even hints at the size and species of fish under the boat! We removed all the old electronics in the cockpit, leaving us with two 5-inch instrument holes in the cockpit plus the four 2-inch holes in the bottom. We removed most — not all — of the old wires, and we installed a VHF radio and a stereo speaker in the two 5-inch cockpit bulkhead holes. Plugging the four 2-inch bottom holes was a much different story.

We bought West System epoxy with both fast and slow hardeners and a 4-foot length of 3-inch-wide fiberglass tape for the bottom hole plugging job. To make the holes accessible inside the boat, we moved the stores and cleared a space around them.

Removing the depth sounder transducers and knot meters required a little force — they’d been in the hull for more than 30 years! Once they were out of the boat, the old tapered holes were cleaned of any old sealer. This is best done from outside the boat; a Dremel tool with a small grinding disk removed the sealer. The area around the four holes inside the boat was cleaned and then sealed with two crisscrossed layers of the 3-inch-wide fiberglass tape over the holes and West System epoxy with its red-colored fast hardener (we love West System epoxy with the pump handle mixers). We let the inside hole covers set overnight, put the stores back in place the next day and then started on the outside.

The outside required cutting 2-inch diameter circles of tape, soaking them in West System epoxy with slow hardener and stuffing them in the holes, making certain there were no air bubbles. Each hole required four 2-inch diameter fiberglass cloth plugs to fill the holes to the outside edge of the bottom. We allowed each layer to harden overnight. The last application covered the holes completely with no air bubbles. Again, after letting it set overnight, we sanded the area smooth. When we painted the bottom it was nearly impossible to tell where the holes had been. We sleep better with four fewer big holes in the boat. Needless to say, the four plugged holes haven’t leaked.

Richard de Grasse and his wife Kathy live on their Tartan sloop Endeavour in southern waters in the winter and summer at Islesboro, Maine.

By Ocean Navigator