Just a thought, while the string in the cockpit idea works well, think about a knockdown and all the "stuff" you have in the cockpit landing on the seat bottom and forcing it open by pulling out the screw eyes and such you rig it with...need to think about the possible forces involved when using something to keep a hatch shut. Last thing you need is an open hatch...of course, if all you do is go out in good weather in the lake, then nevermind....