One Betsie Bay Kayak owner had exactly that experience. His kayak was on his roof rack upside-down, and the hatch broke his windshield when the cover blew! After that, BBK started putting small vents in the hatch covers themselves to relieve pressure during transport. I think they must have finally graduated to a bulkhead breather, because the demo boats at the symposium didn't have these in-hatch-lid breathers.

Dean

: If you're going to use a hatch with no latches and a positive seal, you'll
: need to vent the bulkheads to prevent pressure buildup on warm days. Can
: you imagine paddling along on a sunny day and suddenly POOM!, your hatch
: cover blows off? ;-)

: All it takes is a tiny hole. On the foam bulkheads of my plastic boat, I
: installed pieces of plastic aerosol spray can tubing (the skinny red tubes
: that come with WD-40 and other sprays). They provide plenty of airflow,
: but the hole is too small to pass any significant amount of water,
: especially considering that the compartments are otherwise air tight.