More magnets, I used about 8 pairs per side. Do a test to see how much your sealing foam will compress with the magnets you are going to use, so you will actually get a flush hatch. I got lucky thru no fault of my own.

: I am beginning hatch construction on my latest boat and I will be
: using rare earth magnets. I have 1/8" x 1/2" round I
: plan to use placing about 10 pairs per hatch. I have some great
: flexible ply for rims and shims so I will end up with a flush
: hatch. I may also use carbon fiber to cover the magnet
: containing rims for cosmetic purposes. I expect to take great
: care to seal the mags in epoxy to avoid water damage. I am
: posting pics at heirloomkayak.com and if anybody has well
: intentioned advice or comments I would love to hear them.
: My next major undertaking will be a skeg upgrade for existing
: boats.
: Robert, visionary