zamalek wrote: ...however water hydraulics,etc do not behave like that.Look at how easily a 90kg person is lifted out of the back of a double ski.
It doesn't take much to be taken out of a seat that has nothing to hold you in it. I would not use this analogy and compare to that t all.
40kg or 120kg, if the water is pushing against your ski you will be sucked out of your seat no problem. More accurately, your ski will be pushed away from you, because it presents more resistance to the water than your body in the seat.
I do agree surf an create either huge pressure or suction on the hatch cover. I do whitewater and the sprayskirt over the cockpit is subject to similar forces. Yes, they do on occasion give out, but they are meant to be removable through stretching. To solve this problem, big water paddlers use non-stretchable or locked down perimeters on their skirts - the only way to take them off is by releasing a lever or cut them open. Watch for instance the Hallo Effect for paddling the White Nile in Uganda.
This Epic cover is kind of like that - at least by design, it should not come off as long as the little lock works fine. And there is an easy fix if it doesn't - get a new one or rig-up a little locking mechanism for the free rope lengths, like they have on yachts to fix the ropes when needed and release when not needed. So a $5 piece of added hardware could secure the ropes such that they do not slip out of position even if the original lock tends to slip (which I do not know if it does or not).
To be clear, I'm not defending the design or implementation of this thing, nor am I passing judgment on whether it could/should have been different. And especially since I have yet to see one in the flesh myself - just throwing some thoughts out there and potential things people can try. Hopefully, there are no other not so obvious potential flaws (such as a rounded hatch rim that just wont offer enough leverage for the cover to stay on).