The hatch spacer is temporarily wired to the top of the rear deck. The hatch opening is marked using the inside of the spacer as a template. Once the hatch opening is marked out, the spacer is removed.
After tracing the opening I used an exacto knife to score the marked outline. This made it more visible and broke the top layer of wood fibers, which limits the amount of splintering during the cut.
The manual recommends that you start the cut by drilling enough 1/16" holes to slip the saw blade through. I prefer to use an exacto knife. I simply pushed the tip of the blade completely through the deck. Then I cut through the deck for a long enough distance to accommodate the saw blade. This makes a finer kerf than drilling holes. Be sure to use a new blade and eye protection if you do it this way.
This is a Japanese bonsai saw sold by CLC. It's razor sharp and cuts on the backstroke for maximum control. Here it is slid into the opening made with the exacto knife. I like manually powered cutting tools. If they're properly sharpened, they don't take much effort to cut through okoume or sapele. Since they cut at a slower pace than power tools, you don't get into as much trouble as with an electric saw. As soon as you see it moving from the cut line, you can stop and adjust. As soon as you feel pain, you automatically stop. There may be a nicked finger, but it's still attached to the hand. Finally, they're quiet enough to use when people are sleeping.
The cut is continued all the way around marked opening. Note the fine, clean kerf left by the bonsai saw.
Here is the completed hatch opening. You can also see the back of the rear bulkhead, the top of the rear former (covered in clear packing tape) and the tacks between the wires. The lighter color around the edges is where I cleaned off the cut with some #220 sandpaper.
While the rest of the hatch assembly is being built, the stiffener is attched to the hatch and both are placed in an out of the way spot to cure under the heat of a 40-watt lamp (shop temperature was only 50 degrees).
This shows the hatch sill, rim and spacer all assembled and clamped to the bottom of the rear deack hatch opening. The copper wires are used for the initial alignment, only, and are not needed once the clamps are in place. The holes are pre-drilled by CLC through the deck, spacer and sill. Have a pair of needle-nosed pliers on hand to make it easier to thread the wires through the deck. Sharp-eyed viewers may also notice the 4 mm polyethylene sheet inside the hatch compartment to catch any drips.
The manual recommends that the rim be added after everything else has cured. This is probably because there's no room for all the needed clamps. But by using office supply type clips (a blue one is visible on the left) to hold the rim in place, everything can be assembled in one go. This saves time and epoxy. Assembling the hatch cover, stiffener, sill rim and spacer took 3 oz of epoxy mixed with woodflour.
Here it is with all the clamps off, ready for sanding and final epoxy coats. I was able to work cleanly, so sanding is going to be minimal. By cutting an epoxy stirring stick to the right shape, I was able to remove virtually all the ooze before it set. The plastic protecting the interior from drips & globs is also visible.