At this point in the construction, the hatches remain simple plywood cutouts from the cockpit sole. The two pieces simply rest on the longitudinal cockpit beams.
I am now faced with coming up with a way to make these hatches essentially water-resistant--that is, leak proof enough to resist normal amounts of rainwater, washdowns, and sea spray from normal usage. I have no need, nor intention, to make the hatches completely watertight.
If possible, I hope to keep the hatches flush (or nearly so) with the surrounding sole. I have not yet determined what the final covering of the sole will be--wood or paint.
I've been brainstorming a few ideas about how to make the hatches reasonably waterproof, and have come up with a couple possible solutions. Don't bother telling me I should have engineered this solution before building; I know that, but that's simply not the way I work--often to my detriment, but then I usually find the answers afterwards anyway.
I am seeking any and all input on this issue. To aid in your visualizing the situation as it currently stands, please refer to the following photos.
This shows the opening with the larger of the two hatches removed. The plywood rests on the longitudinal cockpit beams, with about 7/8" of flat bearing space. The beam itself extends beyond the fixed cockpit deck another 7/8", for a total width of about 1-3/4".
One thing that must be avoided in the answer to this problem is that the flat bearing surface of the deck beams must not have direct contact with water on a regular basis. In other words, installing some sort of scupper channel on the inside edges of these beams, which would collect the water conveniently, is not acceptable, since all water would enter the gap between the hatch and the sole and it is likely that water would stagnate on that flat area. This would lead to eventual rot and other problems, even if the area is epoxy-sealed. It's just not sound, long-term practice to allow this to happen.
Therefore, the solution needs to prevent this occurrence. Minor and isolated amounts of water getting into this joint are natural, and can be tolerated by the construction. The key is that I don't want this to be a regular and normal occurrence. I need to keep the water away from the top of the deck beam.
The 7/8" bearing surface of the deck beam is required to remain flat in order to properly support the sole hatches. Therefore, applying a bevel of some sort, while on the surface an easy solution, will not work. I also don't want to reduce the width of that bearing surface, since the sole hatches, being in the middle of the main part of the cockpit, will bear the brunt of usage and weight.
There is room (and access) outboard of the longitudinal deck beams, and one solution we've knocked around involves installing some channels beneath the sole, outboard of the beams, and extending the hatches over the top of the beams so that the new edge would allow drainage into this channel. Of course a cut through the top of the cockpit sole would be required to open up the new channel, and possibly some additional reinforcement beneath the sole.
By rabbetting the upper portion of the edges of the existing flush hatches, as well as the existing cockpit sole above the beams (say, 3/8" of the 3/4" thickness), then installing new 3/8" plywood "wings" to the center hatches, this solution seems like it might be the easiest--and perhaps the most effective. Obviously, any potential solution will most likely require some substantial cutting and reconfiguration of the area, but that can be dealt with easily enough.
Another possibility, though less savory, was actually my first thought: make the center hatches a bit taller than the surrounding sole, with the new edges extending into a routed scupper around the edges. I would prefer, however, to maintain the flush nature of the hatches.
Note that any scuppers installed around the hatches will end up plumbed at the forward (lowest) edge for overboard drainage, probably teed into the main cockpit scuppers.
I am interested in any and all thoughts, and open to suggestions based on the ultimate requirements. If my descriptions are unclear, please ask for clarification. Thanks!
