Refitting dinghy floors

Feb 28, 2011

The day my foot went through the old, rotted floorboard as I stepped into our dinghy seemed an appropriate time to consider a bit of a refit for Dinkum. He’s been around the world, our 10-foot Avon inflatable, and the Hypalon tubes and boat bottom are in fine shape — still air and water tight thanks to a few well-placed decorative patches. But the original plywood floor was another story altogether.

The first step was to find the appropriate replacement wood for the floor. The original floorboards were 3/8-inch thick and because of the various metal fittings used in assembly, the replacement boards had to be the same. Marine-grade plywood was essential since the floor was usually exposed to the elements and often immersed in fresh (and occasionally salt) water. The four-foot by eight-foot sheet of 3/8-inch marine plywood was the single most expensive part of the refit at $78.

The second step was to fit the three boards to the plywood sheet and trace rough shapes on it. These three rough shapes were cut out using a circular saw so I would have convenient-sized boards to work with. Onto each new floorboard, I then drew the correct, detailed outline of the original. Straight cuts were made with the circular saw and a simple handsaw where needed; curved cuts were made with a jigsaw.

Of the three floorboards, the aft two are joined by an alloy extrusion that is friction-fit permanently to one of the boards. This extrusion had to be cut from the old board, then thoroughly cleaned of the old wood. It would eventually be fitted to the replacement floorboard when complete.

The forward two floorboards interlock using overlapping cleats that are an integral part of the back of the boards: two tongues on one floorboard and one tongue on the other fit into corresponding openings on the opposite floorboard. So while the visible, top edges of the two boards meet cleanly, underneath a series of three alternating tongues give the pair of boards a sturdy but flexible joint. From the end cuts of the plywood sheet, I cut the eight-inch-wide strips for the cleats.

Each cleat was then cut to form the interlocking shape between the two floorboards. The fit does not have to be tight or precise since their purpose is to maintain the boards level with each other. The alignment of the boards is accomplished naturally by the shape of the tubes when the dinghy is inflated.

The cleats were attached to the forward and middle boards using stainless-steel flathead wood screws. Pilot holes were drilled in both the cleat and in the floorboard. As shown in the photograph, I wrapped tape around the drill bit to mark the desired hole depth in order to keep me from drilling completely through the floorboard. The screw heads were countersunk level with the wood surface.

The cleats were temporarily assembled to the floorboards and the finish cuts made through both layers of ply simultaneously. I then used a router with a quarter-round bit to finish all exposed edges of the floorboards and cleats. At this point, all of the woodwork was complete.

Because the floorboards live in a wet environment, I decided to completely coat all of the boards with West System epoxy to form a durable waterproof seal. I cut the epoxy with methyl-ethyl ketone (MEK) to make it flow better and to improve the epoxy’s penetration of the wood. For the two floorboards with the cleats, I started by coating the mating surfaces of the floorboard-cleat pair with epoxy. I then positioned the cleats and fixed them in place with the stainless-steel screws. Finally the assembled pairs were ‘painted’ with epoxy. When the epoxy set, the assemblies became permanent.

Working with small portions of West System, I painted all of the floorboards with two coats. I especially concentrated on the edges of the boards, ensuring that epoxy penetrated well into the plywood.

I happened to have some two-part Interlux Interprotect 2000 epoxy barrier paint left over from some work on Gryphon (don’t ask) and I decided to finish the floorboards to a trendy flat gray. The epoxy paint would add to the durability of the floorboards’ finish and I now had the option to add a non-skid component to the final coat. After one complete coat of gray paint to all of the boards, I outlined the upper surface of all three boards with masking tape. The final coat of Interlux paint was mixed with Pettit 9900 Skidless Compound before application. The result was a rough surface that provides excellent traction even when wet.

While I was at it, I painted the transom of the dinghy and the wooden oars with the same epoxy paint. The color scheme has received innumerable comments (some even positive) and the new floor is still serving us well after many months and miles.

Thanks to Walter Garimort and Vern Thompson at Penns Landing Marina in Tortola, BVI, for the good advice and welcome assistance — and for letting me mess up their workshop not mine.

Jeff Williams, along with his wife Raine, regurgitated the anchor in Tortola and recently cruised across the South Pacific to New Zealand on their J/40, Gryphon.

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