Dan,

I also use cut-down mini-cell foam, though I cut mine with an exacto knife. I bet a bandsaw would be a lot faster and smoother.

It makes sense to me that the rim is not necessary when using minicell. The standard foam from CLC is open cell and needs to be squished hard to keep water from working through it (which it always does anyway). I can see that if squishing is not needed, neither is the rim.

If the rim is there for mechanical reinforcement, that'd work just as well on the bottom of the sill as on top.

Laszlo

The hatches on my Merganser hybrid sit perfectly flush and don't leak. I installed 4mm plywood lips without the extra ring, and applied 1/4" x 3/4" closed cell weatherstripping on the lips, not the hatch covers. -Wes

Wes,

Do you have picture of this?

Dan 

I also wanted flush, really flush hatches, ended up with a single layer of okume then the lip, sealed with a double layer of A/C insulation 1/4 in neoprene stuff.

The final product is now flush, after compression with two bungie hooks on bow hatch and four bungie hooks on aft.

Pictures are here,

http://outdoors.webshots.com/photo/2875951280100154152SUdSAe

The warping of the hatches during the gluing of the stiffeners was the worst part.

BUT after a day os plowing through waves, or praticing a few rolls I have only a few drops of water inside.

Ted B

If you want pics of how they look NOW, after one summer of use, let me know.

Dan,
Posting photos on this site is too much of a hassle, so I put them on my own website at http://twofootartist.com/merganser-construction-notes/ 
Scroll to the end of the page to see them. Left click on them to enlarge to full screen.
As I took these photos I noticed that the front hatch, which is rarely opened, has compressed the foam so it now sits slightly lower than the deck. I may replace the foam in the Spring.
I also noticed that I had mis-stated how I built these. There is a 4mm spacer between the hatch lips and the deck.
I made my own bungee hold-downs similar to the CLC items.
-Wes

Thanks Wes!

That looks great, a really clean detail. I wonder if minicel foam would be as waterproof and compress less.

Dan

btw, I just rough sanded the SW16h deck with 80 grit and the hollow I was worried about is now gone!