: You can also buy latches for hatches that use rare-earth magnets as keys to
: open them.

: The problem is that once you put rare-earth magnets on your boat, you can't
: use a compass any longer, as it will not read reliably.

Even with the powerful rare earth magnets the magentic field drops of very quickly. As long as you keep the compass about 2 feet away from the magnets you should be fine. You can test this. Try bring the magnet closer to the compass until you see it move. Try different orientations and from different directions. If you can't make the compass move from a give distance, it won't effect your course.