: I didn't think about having gear bang on the hatch when the yak is inverted.
: Hmmmmm. Damn. Maybe an internal spiderweb of bungies to hold everything
: down or up depending on which way is up is the answer?

: Larry

The strength/number of the magnets you use and the width and thickness
of the gasket will determine the holding power on the hatch cover.

I use a magnet/gasket arrangement that results in my JUST being able to
pry off ONE SIDE of the hatch with three fingers. I've had more than a few
people who couldn't remove my hatch covers. I guess I have strong hands.

I think the idea of gear popping this hatch arrangement is less likely than the
same boat, with straps, sinking because of a leaking hatch gasket.

Straps are useless to seal a gasket on any deck that has a1" or less, rise at the deck centerline.
There is just no downward pressure. Sure, the cover won't come off but you could take on a lot
of water.

I've seen many hatches with straps, full of water after just a few waves.

As I've said, I'm able to pry open one side. Just. Any object inside the boat hitting the cover will
distribute the force much more. It can only hit 1" closer to the hatch center because of the internal
lip. Plus, there is just no distance for an object to build enough velocity to begin to achieve the force
needed to dislodge the cover. I wouldn't be surprised to find you could lift the boat with a line secured
to the center of the hatch cover. You might even be able to lift the kayak with the paddler in it.

I've gone to using a small wooden pry bar to open my hatches. If the seal on the gasket is good, which
it is with the magnets, then you'll have an even tighter seal when your boat hits cold water.

If you're upside down, water pressure will apply even more force, holding the hatch cover in place.

As Nick has said, the effect on a compass is nil over short distance.

All the best,
Rob