I like the comments made regarding the 1/4" wide gasket material versus wider stuff, as my own experience seems to bear it out. On my second OI I'm using either 3/8" or 1/4", can't really recall offhand (although the boat's within fifteen feet of me here in camp right now, but strapped on the racks and I'm too lazy to go look). A couple of notes:

I also like internal bungees. I had a knot slip and there was scarcely enough tension to make the bungee stay on the hook, yet the seal was watertight as ever, and even stayed on at highway speed while riding the racks. Yeah, I'm a colossal DA sometimes..... Anyway, the pressure required is surprisingly light if the arrangement has been carefully put together.

I add Redfish/Greenley style soft padeye webbing loops to my hatch covers to make 'em easy to pop open. Align the loop with the "slipstream" so they don't splash. In the photo below you can see the bottom end of the soft padeye in the hatch lid. It also tells me which way the cover goes on.

If you can't get the hatches to stop leaking, we can always get Tony Olsen to trot out his spiel on silicone counter-seals.

No hatches are 100% watertight in my world. None. The VCP's on my 'Kapp come close, but the homemade articles give 'em a run for the money when done right. I was going to use VCP/Kajak Sport "rubba bubbas" on this boat, except I finally decided they were too heavy, too expensive, and too ugly to use on a pretty lightweight stripper.

http://mysite.verizon.net/NGC704/newOI/Page_9.htm

: I'm a bit disappointed in my hatches - they're a tad shy of dry
: (actually several tads) and I'm unsure what I failed to do. I
: thought I'd followed Vaclavs' directions to the T - but the end
: result suggests otherwise. I'm wondering if the deck shape
: changed significantly , though I removed it, made the inner lip,
: and joined the halves again before the epoxy had fully cured.
: Perhaps thicker gasket would help - though finding 5/16 (I used
: 3/16 to make it, 1/4" to replace) has been challenging.

: I'm always willing to learn from the experts. Thanks.