Underwater searches

Underwater searches are procedures carried out by divers in order to find a known or suspected target object or objects in a specified search area under water. There are a number of techniques in general use by Commercial, Scientific, Public service, Military, and Recreational divers. Some of these are suitable for Scuba, and some for surface supplied diving. The choice of search technique will depend on logistical factors, terrain, protocol and diver skills.

As a general principle, a search method attempts to provide 100% coverage of the search area. this is greatly influenced by the width of the sweep. In conditions of zero visibility this is as far as the diver can feel with his hands while proceeding along the pattern. When visibility is better, it depends on the distance at which the target can be seen from the pattern. In all cases then, the pattern should be accurate and completely cover the search area without excessive redundancy or missed areas. Overlap is needed to compensate for inaccuracy.

An underwater circular search is a procedure conducted by a diver swimming at a series of distances (radii) around a fixed reference point. The circular search is simple and requires little equipment. It is useful where the position of the objects of the search is known with reasonable accuracy.

The general procedure is to start from a fixed central point, and to search the circumference of a circle where the radius is defined by a search line anchored at the central point. The radius of the circle is dependent on visibility, and is increased after each circle has been completed, by an amount which allows the diver to either see or feel an overlap between the current arc and the previous arc.

One end of the distance line is carried by the diver and the other is attached to the datum position by any appropriate method. E.g. clipped to the base of a shot line, pegged into the bottom, tied to a fixed object on the bottom or held by another diver. The diver may tow a surface marker buoy if conditions allow. The diver unreels a section of distance line appropriate to the visibility and mark his start position by a peg, loose marker, compass heading, or a pre-laid marker line extending outwards from the datum position. Then, keeping the line taut, the diver swims in a circle with the line as radius, searching visually or by feel until back at the start position. He then unreels another section of line of the same length and repeats the procedure until he finds the object, runs into obstacles or runs out of line, air or time.

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