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From a Bare Hull: The Deck (Page 5)

Sheathing the Decks
While the first layer of plywood was intended only to serve as a final cosmetic surface from beneath, the upper layer was to be the main structural component of the deck construction. For this, I chose 9mm (3.8") Meranti marine plywood, which I had used throughout the project. I purchased five sheets to complete the job.

NOTE: I wanted to show many photos of the process, so the photos, while sequential from top to bottom, might not always correspond directly with the adjacent text.

I began at the stem, where I made a template for a small piece of plywood to fill the forwardmost portion of the deck, from the forward deck beam to the breasthook. Not only did this take care of a difficult area right off the bat, it also allowed me to stagger the remaining joints, so that none of the joints on the top layer of plywood would be directly above those beneath. I immediately installed this piece by troweling on (with a V-notch trowel) a bed of thickened epoxy beneath, then screwing the piece into place. This provided a solid starting point for the subsequent full sheets.

I continued with the two largest pieces: nearly full sheets that spanned the entire foredeck. I had laid the first layer (beadboard) so that a full sheet spanned the centerline, mostly for the most seamless appearance inside. Therefore, I laid out the top layer so that there was one sheet on each side of the centerline, with a seam down the centerline. This allowed two sheets to cover the entire foredeck back to the curved beam marking the forward end of the cabin trunk.

After marking the centerline, I made two additional marks, one on each side of the centerline: using my long metal ruler, I marked an offset line 2" (one ruler width) on each side of, and parallel to, the centerline. This line would be useful for reasons that will soon become apparent. Since the hull, by design, still projected about 3/8" above the deck underlayment, cutting the sheets to fit would require a multi-step process involving scribing.

I laid one full sheet of plywood on the deck, butted up to the centerline and against the small piece beneath the breasthook. Much of the sheet overhung the edge of the boat at the forward end, of course. After checking the alignment, I went outside the boat and traced the edge of the hull onto the underside of the plywood sheet where it overhung. This gave me the basic contour of the hull, to which line I then cut the plywood to rough shape.

With the basic cut made, I realigned the plywood against the 2" offset line, which had the effect of pulling the freshly cut edge clear of the edge of the hull. Setting my dividers to the same 2", I then scribed the inside hull contours (which, because of the old hull-deck joint tabbing, were quite uneven) onto the sheet of plywood. Then, I cut to the new line with my jigsaw. When I moved the sheet of plywood back over 2" to the centerline, the new edge butted cleanly against the inside of the hull (minor adjustments excepted).

When I was satisfied with the fit of the first sheet, I removed it and repeated the process with its near twin on the other side. When both foredeck sheets were cut to fit, I prepared to install them permanently.

I installed one sheet at a time, but this still required large amounts of mixed epoxy. Even with what seemed like a relatively thin layer laid down by the 3/16" notched trowel, each of these large forward sheets required approximately 50 oz. of mixed epoxy, which I then thickened with cabosil to an adhesive viscosity--not too dense, but heavy enough to stand on its own without slumping. On my first sheet, I ran out of epoxy about halfway through, since I had only mixed about 30 ounces (thinking it would be abundant), so I had to hurry to mix a second batch to finish the job. When the whole area was covered with the epoxy, I placed the sheet carefully into position and screwed it in place with 1-1/4" bronze screws, which were long enough to pass through both layers of plywood and into the deck beams. I repeated the process on the second section, this time with enough epoxy to finish the job in one mix. I let the aft edges of the sheets run wild over the interior deck edge (in this case, the curved forward carlin, which I had protected with a number of layers of masking tape for the occasion) for later trimming.

In similar fashion I continued down the decks towards the stern, using much the same techniques described above to cut and fit each piece. For the remaining pieces, though, it was a simple matter to let the interior edges run wild over the carlins, as I would trim them later with a large router, so I had no need for the offset technique described above. Each piece, however, still required two cuts for a proper fit--the rough hull contour cut, followed by the interior hull scribe. Over most of a single day, I completed the remaining pieces, covering each side of the deck as I proceeded. A long the way, I began filling seams and screw holes with any leftover epoxy from a given batch.

With both sidedecks complete all the way to the aft end of the cockpit, I made a pattern for the final piece, which would cover the poop deck. I cut this from a single sheet of plywood to cover the area side to side, so the template was invaluable to allow for accurate sizing and cutting. When the piece was cut, I installed it in the final batch of messy epoxy.

Finally, I chucked a new 1/2" flush cutting pattern bit into my bad-boy router (seen above), and trimmed the inside edges of the decks flush with the carlins. The router made this a breeze, and provided an exceptionally clean and precise cut. I finished up the small sections where the router couldn't reach, against the midships bulkhead, with a hand saw.

While I made all efforts to scribe the plywood closely to the contours of the hull, there were inevitably gaps along each edge, as well as some minor unevenness of the upper hull edge left over from the original deck removal process; all along, I had been counting on the new deck acting as a fair pattern to make up any minor undulations in the hull.

Before I could think about installing the fiberglass sheathing over the decks, I had to fill these gaps, and also fill the countersunk screwholes throughout the deck. I filled these areas with epoxy fairing compound, which I mixed to a very thick consistency and then troweled into the seams as needed. In a few areas, I built up the compound more thickly to help bring the hull edge fair and in line with the decks, most notably near the stem on each side. I left the fill to cure overnight before continuing.

The next day, I sanded the fill to remove any rough edges and to smooth it somewhat in preparation for the next steps. Final deck fairing wouldn't occur until after the fiberglass was installed, so I didn't worry about minor unfairness and the like at this stage. I also scuffed all the epoxy fill covering the screw heads throughout the deck.

Next, I used a router equipped with a 1/2" roundover bit to mill a smooth curve into the hull-deck edge, partly for its ultimate appearance but more importantly to provide a smooth curve over which I could laminate the fiberglass deck sheathing later. The router did a good job cleaning up the edge; because of the flare in the forward sections of the hull, I had to make the cut in three passes on each side, since the bit dug deeper into the boat in these areas.

Finally, I used a palm sander and coarse sandpaper to put the final touches on the newly-routed joint, further smoothing it and removing any rough edges. This was the final step required before declaring the decks ready for fiberglass.

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