: I am working on my first strip kayak and am about to get to the hatches. I
: want to make them flush with the deck and avoid straps across them if at
: all possible. I've seen magnets used to do this, but I don't remember
: exactly how that worked. I'm also trying to figure out how to achieve a
: watertight seal. Any advice? Thanks!!

First, if your hatch cover and deck lip do not mate perfectly it doesn't
matter how you hold the hatch cover down, it will leak.

When we join the deck and hull, there will always be some distortion of
the deck.

We see this as a hatch cut out that does not match the deck shape.
Most often I find the shape of the hatch cut-out is a tighter arc than
the deck. Force is most often applied to the lower side/edges of the hatch
cover. So I spread that arc slightly more than the deck shape at the cut-out
sight, which will make a better seal later.

You can reshape the hatch cut-out by installing a rib, to try to force
the hatch to match the deck shape. This can cause stressed glass problems

I sand the glass off the inside of the hatch cut-out. I reshape the hatch
cut-out by applying new glass to the inside and taping the hatch cut-out
to the deck close to the cockpit. Put a layer of wax paper down first.
The deck shape nearer the cockpit will be close to, but broader than
the shape where the hatch cut-out came from.

Then install your waterproof gasket on the deck lip. This creates a barrier
for the water to climb. Yes, it's not much, but everything counts.

I now use 8 pairs of 3/4" X 1/8" magnets for each hatch cover. This has A LOT
of holding power. These are so powerful they can reshape the hatch cover. I've
had a couple problems where the magnet poles where not aligned correctly and the
repelling force bent the hatch cover out of shape. The magnets are marked with
a red dot indicating the north pole, but the epoxy can wash this mark off, so
you need to be careful. As I've said before, it is critical to totally seal
the magnets under glass to waterproof them, or they rust VERY fast.

I have to place a webbing loop on the hatch cover to have something to grab,
to be able to pull the hatch cover off. If you think the hatch cover can come off by
itself, you're dreaming.

And, IF you have a good seal with your gasket, the air pressure difference
created when your boat hull hits that cool water, most of the time, will add
holding force to the hatch cover. And if you are doing a fish count (upside down)
the water pressure will press hard on your hatch cover.

I also install and releasable hatch cover tether, so I won't drop the hatch
cover and have it slide off down the seaweed into some crevice.

I hope this helps.

All the best,
Rob