Put your hatch on for a few days, all clipped down the way it should be. Then take it off and look at the neoprene gasket. You should be able to see where it has been compressed. Look for places which are not get compressed well. You may need to add more gasket or rearrange the system to get good compression all the way around the gasket.

: I´ve cut out hatches in the deck the way Nick describes it in his book.The
: hatch is resting on a list of playwood glued to the deck from the inside
: of the kayak. The list has a width 20 mm and is covered with 7 mm
: neoprene. The hatches is held down with 8 small turnable clips.I thougt
: the neoprene would make it watertight. But the water is getting in
: someway. I suppose this is a common problem. Please help!
: Fritjof Karlsson