ABSTRACT
Where is the boat? This question is on many an underwater explorer’s mind at dive’s end. If underwater visibility matched that of air, navigation over several hundred meters would not be an issue; but even in clear tropical water a diver can see barely 100 m, and much less than this in temperate waters made murky by plankton. For the sport diver, the underwater compass is the primary tool for keeping track of direction. To succeed, compass navigation must be supplemented by visual recognition of underwater features (caves, walls, etc.) and “dead reckoning” techniques such as counting one’s fin kicks along a specific compass bearing. The sight of the boat’s anchor chain at the end of a dive is a welcome reward for good navigation. With our eyes and with a compass on the wrist we can at least avoid becoming dangerously lost.
