XV. Installing the Deck
Building the Core Sound 20
August 8, 2008
NOTE: This article is divided into chapters. Click here for the Table of Contents.
After giving the interior paint a day to cure to a hard durable finish, it was time to install the deck. Although great care must be taken during this process to prevent unsightly seams wherever one panel joins another, most of the process is fairly straightforward.
Choosing to work our way from bow to stern, we began by laying a 4x8 sheet of Okoume plywood along the front half of the bow, with the long edge of the plywood running straight down the centerline of the deck. While holding the sheet in place, we traced the perimeter of the hull and each piece of deck framing with a pen.
Next, we cut out the traced outline of the panel using a cordless circular saw. We deliberately cut 1/4" outside the line so the panel could be planed down to an exact fit later, after gluing.
Then we laid out the panel on the workbench and epoxy coated the underside to seal the wood. Using our traced lines as a reference, we took care not to seal the panel anywhere it would sit on top of the deck framing. This ensures that the glue can establish a good "soak-in" bond with the wood when installing it later. Any surfaces that will not receive glue, however, we sealed with three good coats of epoxy. We repeated these steps for all six panels that comprise the deck.
Meanwhile, we also roughed up the tops of the deck framing lumber with 80-grit sandpaper to ensure good "tooth" for the glue-bond. Then we wiped everything down with acetone to remove sawdust and any impurities (such as paint, sap, or dirt) from the wood.
When each panel was ready to be attached, we wetted out the tops of the deck framing and the dry gluing surfaces on the underside of each panel with unthickened epoxy. Then we immediately mixed up another batch of epoxy semi-thickened with fumed silica to a slightly-thicker-than-oatmeal consistency. We scooped this thickened epoxy into a heavy-duty Ziploc bag, trimmed one corner of the bag, and squeezed it onto the deck framing in a nice, even bead of glue (like a cake-decorator's frosting bag).
The epoxy cures quickly in the Georgia heat, so as soon as our bead of glue was laid, we pressed the corresponding panel into place, using our traced lines and a few reference marks to ensure we seated it correctly. Then we used an array of clamps, straps, weights, and tape to hold the panel securely in place without need for any mechanical fasteners. This is important since we plan to finish our deck "bright" (clear-coated with varnish) and don't want to have any unsightly fastener marks showing through.
Although we could have cut, sealed, prepped, and glued all six panels at once, we thought it prudent to proceed two panels at a time. So, we glued the first two panels in place and waited for the glue to cure overnight before cutting the next twoand so on. This allowed us to ensure that each new pair of panels butted up tightly against the previous (glued) panels before tracing and cutting them out. Although this turned the six-panel deck job into a three- or four-day process, our patience paid off. Our seams came out very tight and we had plenty of time to carefully select and arrange each new panel to achieve the best color and grain match. (Fortunately, at the very beginning of the build, we had the foresight to set aside our best three color- and grain-matched sheets of plywood to use for the deck.)
Once all six panels of the deck were attached securely to the deck framing, we used a block plane to shave down the oversized panels to make them flush with the hull. Then we rounded the edges with 1/4" roundover bit, first taping off the deck with masking tape so that the router wouldn't tear out the woodgrain. The results were terrific. Before using the router, however, it's important to ensure that all seams and joints are tight and smooth so that the bearing on the roundover bit can ride smoothly on the surface. Any bumps in its path will produce corresponding irregularities in the rounded-over edge.
Next, we sanded the deck with 220-grit sandpaper until it was smooth and uniform in appearance. Then we wiped the dust off with wet rags, deliberately moistening the wood in order to raise the grain. Once dry, we sanded the deck again with 220-grit sandpaper to take off the "fuzz" raised by the moisture. This process ensures that the deck will be very smooth, and that the wet epoxy won't raise the grain later to produce hard bumps in the fiberglass.
With the deck sanded, we wiped it down one more time with acetone to ensure a dust-free surface. Then we coated the entire deck in a thin coat of epoxy, allowing it to soak into the wood and cure for a few hours. This first coat is always exciting, as it really brings out the beauty and color of the wood.
As soon as the first coat of epoxy had lost most of its tackiness, we laid out a layer of 4 oz. fiberglass cloth and began wetting it out. It is important to apply this layer before the previous layer cures fully in order to achieve a good chemical bond. Many builders skip the pre-coat step and begin with saturating the fiberglass cloth, but we've found that starting with a thin, soak-in coat of epoxy results in a much better bond between the cloth and the hull. Otherwise, there is a risk that the cloth may hold all of the epoxy and "starve" the wood, preventing a good soak-in bond.
Over the next several hours, we applied five thin fill coats of epoxy to bury the fiberglass weave. The last two fill coats were technically unnecessary, but since the 4 oz. cloth is really easy to accidentally sand through, we thought it prudent to build up some extra (sacrificial) thickness.
The next day, we spent three hours sanding the deck with the random orbital sander to eliminate the mottled epoxy texture left behind by the foam roller. It was hard work, but the resulting surface came out superbly smooth. We also trimmed the inside perimeter of the cockpit, the hatches, and the front mast step using a flush-cut bit on the router. Thanks to the fiberglass, the trimmed edges came out perfectly, with no grain tear-out.
Next, we cut strips of 3/8" thick Meranti plywood to create a rim around each hatch opening in the deck. We glued the rims in using thickened epoxy, taking care to mask off the deck first to prevent a mess. Some mess is inevitable, but by working slow and cleaning up carefully, we ended up with a very nice rim installation. Initially, we gave our rims a height above deck of 2", but later we cut them down to 1-1/4" high, which was visibly better proportioned to the boat, and allowed our hatch covers to be low profile (just 1-1/2" tall).
For the hatch covers, we built a solid frame of mahogany, topped with 1/4" Okoume plywood to keep the weight and bulk down. Rather than glue the plywood panel on top of the frame (as designed in the plans), we chose to inset the panel into the mahogany frame to hide the plywood edges. It takes more work, but is well worth it.
Once the hatch covers were glued together, we radiused the top edge of the mahogany frame with 1/4" roundover bit and radiused the vertical corners with 1/2" roundover bit to match the radiused corners of the inset Okoume panel. Now we have elegant hatches that will really complement the beauty of the deck.
Next, we began work on the cockpit coaming which serves both as a backrest and to divert deckwater away from the interior. The coaming is made from 1/4" Okoume plywood, but the wood is too stiff to turn the 10" and 15" radius corners at each end of the cockpit. Rather than laminate thinner pieces together to make the corner pieces, we elected to steambend the wood using boiling water and towels.
With the pieces cut roughly to size, we wrapped them in the towels and poured on boiling water to heat the wood. The towels help hold the heat longer, and once the core temperature of the wood is hot enough, it becomes noticeably more flexible. This process is even more effective if you pre-soak the wood in water overnight and also wrap the hot towels in builder's plastic to hold in more heat when applying the boiling water, but we managed to get the bends we needed without pre-soaking. Then we left the pieces clamped to the boat for a full day so they could dry out thoroughly and settle into their new, curved shape.
A day later, we cut the curved pieces down closer to the finished size and glued them in using thickened epoxy. After giving them a full 24 hours to cure, we released the clamps and installed the long side pieces that join the fore and aft curved sections to complete the coaming. Once again, some creative clamping was needed throughout this process, but we managed to form and attach our coaming without using mechanical fasteners so that it can be finished bright.
To enhance the durability and appearance of the 1/4" coaming, we next added a 1/4" thick layer of mahogany around the outside. This will give the coaming a mahogany appearance when viewed from the outside that compliments the mahogany accents used elsewhere on the hatches, tiller, and gunwales. The boiling water and hot towel trick didn't work for the solid mahogany, so instead we built a makeshift steam box using PVC tubing capped at both ends with a 1/2" hole in one end to let steam in and a smaller 1/8" hole in the other end to let steam out. Then we inserted our mahogany strips, replaced the cap, and poised it over a steaming kettle until the wood inside was piping hot, making it very easy to wrap it around the radiused corners of the coaming.
Once the mahogany strips were glued around the exterior of the coaming, we sanded everything smooth and ran around the inside and outside edges of the top of the coaming with the router using a 1/4" roundover bit. This excellent idea came from Ray Frechette of Great Falls Boatworks, and it yields a very attractively rounded, sturdy-looking cockpit rim.
With the coaming installed, our boat is finally structurally complete. Next, we will concentrate on building the masts and adding strategic reinforcements to our deck to accept the hardware that will control the sails. Before long, we'll be varnishing and then sailing!
© 2008, Wesley Kisting