: I'm curious to know if anyone has done any measurement or studies involving
: the magnet diameter, placement, number, and proximity to each other before
: and after gasket compression (gasket type) to provide a decent or optimum
: seal without needing a pry bar to remove them? Good or bad experiences?

As posted before:

I use rare earth magnets on the flush hatches of my kayaks.

You need a magnet to magnet contact for the strength needed to bridge the gap until your gasket compresses.
You must use a soft gasket material that comprsses very well.
Gasket material is available from Newfound Woodworks or I also sell gasket material.

I use the 1/2" diameter X 1/8" thick magnets available from Lee Valley Tool;
http://www.LeeValley.com/

The magnets are recessed into the hatch cover and hatch lip on the deck. I use eight on the hatch cover and eight on the hatch lip. A total of 16 per hatch. This may sound like a lot but I did extensive research and found the number and configuration I'm discribing works the best.
4 per side spaced about 3' apart.

The magnets rust if not totally sealed, so i cover them with a layer of 4 oz. glass.

The waterproofness was tested with rolls at last fall's Newfound Rendezvous.

Aligning the mating pairs is important. MAKE SURE ALL THE POLES ARE ALIGNED SO THE MAGNETS ATTRACT, NOT REPEL!

You MUST BE WARE the magnets will effect any compass placed in proximity.

I found the magnets effected my compass if it came within 18” of the hatch cover.

If you would like more detailed information on making flush hatches closed with rare earth magnets contact me.

All the best,
Rob