When the Hole is Too Big

Making a large stove flue hole smaller for a cabin vent.

Jamie O. Harris

My good old Spencer 35, Onrust

(Dutch word meaning “unrest”) came to me seven years ago with a very nice Dickinson diesel cabin heater mounted on the main bulkhead. I always liked to look at it, but never really used it in my San Francisco Bay waters. In fact the only times I fired it up were a couple of January days doing odd jobs in the boat and then only to see how it worked. Even though it was nice to look at,

the heater took up useful seating space around the cabin table. When the fuel pump packed it up, I had to decide whether to buy a new pump or simply remove the heater to gain more space around the table. Believing strongly that simple boats are best and unused equipment is a burden, I decided to sell it - flue pipe, Charlie Noble and all. Through craigslist I found an eager

buyer who was fitting out his own good old boat and felt a cabin heater fit into his cruising plans. Part of the price he offered was a chromed bronze mushroom ventilator that I could install in the old through deck hole for the flue pipe. When the day came to remove the stove and I received the ventilator, however, I discovered that the flange for the mushroom ventilator was a good inch less in diameter than

The G-10

“donut” glassed in place and cloth cut out of the inner circle before finish sanding.

the one for the heater’s flue pipe. The heater went to its new home anyway but I had a problem to solve. I searched for a while in catalogs

and used equipment shops to see if I could find a wider flange that would fit the ventilator and the existing hole in the deck, but came up with nothing. I toyed with the idea of glassing over the entire hole and cutting a new one, but that seemed like a messy and difficult proposition. The answer came in the form of a

material called G-10. G-10 is a very stiff epoxy that comes in sheets of various thicknesses. I got a small piece of the 3/8” thick sheet at my local boatyard and the yard manager cut a circle for me about 7.5” in diameter, just big enough to overlap the flue pipe deck hole by about an inch all around. He left a clear mark in the exact center of the circle for me. I then used a compass to scribe the new inner hole size to fit the new ventilator flange and carefully cut it out with a jig saw on my home work bench, leaving a donut-shaped piece of G-10. Next I sanded the area around the

hole on the deck and both sides of the G-10 donut to roughen the surfaces and remove most of the gelcoat from

“Onrust’s” cabin with the Dickinson on the bulkhead.

the area that would be covered by the donut. I made a mixture to set the donut in using West System 404 105 epoxy resin with 205 “Fast” hardener. Before the epoxy kicked, I added lots and lots of West High Density Adhesive Filler powder to thicken the resin to the consistency of stiff peanut butter. (Before doing this on the boat, I experimented at home in the shop with various amounts of filler to get the consistency I wanted – soft enough to spread easily, but stiff enough to hold its shape when I created a fillet around the edge of the donut.) I spread the mixture around the

deck hole and firmly pressed the donut into place, being sure that an even amount of paste pressed out all the way around both the inner and outer edges of the donut. Using a small plastic

The finished installation. The “donut” also provides a raised area for positive drainage away from the caulked flange.

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