IX. Seat Hatches
Building the Core Sound 20
May 13, 2008
NOTE: This article is divided into chapters. Click here for the Table of Contents.
After sanding and epoxy-sealing the entire interior, we measured and marked out the four seat hatches which will allow us access to the four bulkheaded compartments inside the seats. There is much to consider here. The seats have to be large enough to accommodate bulky gear like lifejackets and boat fenders, but if the hatch covers are too deep, they won't be able to open fully without hitting the upper deck (which is annoying because it requires someone to hold the cover open while retrieving something from inside the seat). They also have to be positioned where they won't be in the way of the thwart, and where they can be opened conveniently while manning the helm.
We decided to make our hatches 24" long by 12" wide, with the front lip extending 5-3/4" down the front face of the seat (to accommodate a sloped drainage lip all the way around the hatch). Once we pondered the dimensions for awhile, we masked off each hatch perimeter with masking tape and drew the cut lines onto the tape. Besides providing an easy-to-see line, the masking tape helps prevent the plywood grain from tearing out along the edges as we cut it.
We decided to cut the seat hatches using a very thin fine-cut blade on the jigsaw. To start each cut, we used a tiny drill bit (the same thickness as the jigsaw blade) and the Dremel rotary tool to drill a series of five holes in a line, producing a tiny slit for the saw blade to enter. It worked wonderfully well. An hour later, we had cut all four hatches. Although we knew they would came out fine if we took our time, this part of the process was still nerve-wracking because any mistakes here would create a lot of repair work.
With the hatches cut, it quickly became apparent that the front lip of each hatch was too deep. If we ran a sloped drainage channel all the way down to the bottom of the lip, it would intrude too far into the storage lockers and make it difficult to cram large gear into the seats. So, we decided to build the drainage channels with a more moderate slope, dropping only about 3-3/4" instead of 5-3/4" as planned. Either way, it shouldn't make a difference to the external appearance of the hatches, but it does mean a little extra labor to make each drainage channel.
To make it easier to build each hatch, we decided to glue up the frame first by coating the inside of the seat cut-outs with packing tape (to prevent epoxy adhesion) and clamping the framing wood in place. We used 3/4" thick Douglas Fir for the framing lumber, cut it to the sizes and shapes we needed, coated the joints in thickened epoxy, and clamped everything into position exactly as it will be installed later.
A day later, once the epoxy had cured, we had a perfectly fitted frame for each hatch. Thanks to the packing tape, however, we were able to remove these frames and take them in the garage for the rest of the hatch-building process. This may not sound exciting to you, but for us, it meant that we didn't have to make a thousand trips back to the boat for measurements. Each frame provided us with a perfect outline of its corresponding hatch, so we could focus on measuring and cutting the pieces for the drainage channel right there at our table saw! Very convenient!
The first step is to create the sloped "floor" of the drainage channel. Later, we will add an inner "lip" to complete the channel, but the floor must be glued to the frame and allowed to cure first. We settled on making the drainage channel 3/4" wide all the way around the hatch, with a little extra space in the back to allow clearance for the hinge and frame of the hatch cover. Except for the frame, all of the hatch parts are made from 3/8" marine plywood left over from cutting out the bottom panels of the hull.
Since we made the hatch frames from 3/4" thick Douglas Fir, we decided to screw and glue the hatch pieces together. Epoxy gluing alone would probably be adequate, but the screws will give the whole assembly more strength in case anyone ever stands directly on top of our hatches. More importantly, by pre-drilling the parts, we made it easy to re-align everything again later when it came time to glue. We used 3/4" long #8 stainless screws spaced every 6 inches around the perimeter, which also turned out to be more than adequate to provide good pressure for the glue (instead of needing clamps), so there were no clamps to get in the way as we cleaned up the glue squeeze-out on each hatch. In short, screwing the parts together turned out to be superbly convenient, and well worth the trouble of counter-sinking all those screw heads. I will follow the same process if I ever have to build more of these hatches. (I sure hope not! These are ultra labor-intensive to build!)
The next day, we cut the plywood pieces to assemble the inner rim. Here, too, we were smart by using a pneumatic brad nailer to "tack" each part into place with 3/4" 18-gauge brad nails. This made the rim very rigid without needing to wait for the epoxy to cure, allowing us to handle the parts to clean up epoxy drips. This was much smarter than attempting to clamp everything in place, as the clamps would have been in the way, and our clean-up efforts undoubtedly would've knocked some of the parts out of alignment. Better yet, the permanently embedded brad nails will provide mechanical reinforcement to the joints, taking stress off the epoxy-bonded surfaces and making them less likely to pop apart later if they get bumped or banged as we load cargo into the seat lockers.
With the drainage channels structurally complete, we sanded them carefully and epoxy sealed the wood to prevent any problems with rot. Then we set them aside for awhile.
Later, in early July, we glued in the hatch rims and ran around the top edge of the seat with a router to cut the hatch rim approximately 1/16" shorter than the top of the seats. This small gap will permit room for a thin gasket on the underside of the hatch cover to help seal the compartment and prevent water intrusion.
Once installed, the hatch rims not only give a nice "finished" look to the hatch openings but also add welcome stiffness to the seat tops. To ease installation and avoid the need for clamps, we installed each hatch rim with #8 fasteners permanently embedded in the epoxy. The fasteners also mechanically reinforce the glue bond, so our hatches should hold firm even if someone puts their full body weight on top of the hatch cover.
Next, we built the hatch covers. We kept the original seat cutouts for this purpose, but added a rim around the cover that fits down into the drainage channel to discourage water from getting inside. The rim also lends some stiffness to the hatch cover and holds it in the proper shape for a good fit and neat cosmetic appearance.
© 2008, Wesley Kisting