Bill St. John Wilkes, The Handbook of Underwater Exploration, Stein and Day, 1971


If there are no headlands and one is on the open coast, I believe that in the interests of accuracy and safety, it is better for the swimmers to enter the water from a boat cruising parallel to the shore, and take their marks off features on the shore. In this case, especially if a large area has to be swept, it pays to put ranging poles on the beach in pairs, one pole at least 5m behind the other, at the extremities of the search line. Both end men can use them as transits and swim straight towards them. If the first sweep is unsuccessful, then the first set of ranging poles is moved along the beach past the second set and forms another transmit mark for the next stage of the sweep.