Hatches with magnets
I have, for a couple of reasons, rejected magnetic hatches on my kayaks. The magnetic rim must be quite wide – a lot of hatch for a small hole. Furthermore, the magnets have in my opinion the “wrong” holding power profile: good holding power in contact but very little just a few millimeters away. It is an effort to pull the hatch open, but if you get a corner of a jacket or a small string in between, the hatch might be unreliable. With other locking systems, it is the opposite. Rubber chords pull harder with distance and webbing has no flex. I was also concerned about the magnet’s influencing the compass (having had that trouble on the yacht we built 45 years ago: the iron in the ferrocement hull was probably loaded or unloaded with magnets somewhere, and standard yacht compasses didn’t work and had to be replaced by a compass transmitter in the mizzen mast connected to a repeater in the cockpit).
But other kayakers have built excellent magnetic hatches and are happy with them. This fall I got photos and a description from Gustav Borreman in the Netherlands, who based his version on Rob Mack’s (Laughing Loon) method. Here is his description.