NAUI Master Scuba Diver 222 Search and Light Salvage Another compass-controlled search pattern is the expanding box (or square) search pattern (figure 9-3). The dive team swims on a predetermined course for a short distance from the starting point using the kick count or swim time as a control. The divers then turn 90° and swim a slightly longer distance. This procedure is repeated to provide an expanding box shaped pattern (or straight-sided spiral). The degree of expansion on each side is controlled by the visibility. Circular Search The circular search is popular because it is simple and effective in many situations (figure 9-4). This pattern is most useful when there are no underwater obstructions in the area being searched and when visibility is reasonably good. One end of a line is secured firmly in the center of the area to be searched and serves as a hub. One member of a buddy team remains at the anchored end of the line, while the other diver holds onto the line and keeps it taut while swimming circular sweeps to search for the lost object. The diver at the anchored end can face one direction, and will then know when a complete circle has been completed. After each complete circle, the diver at the anchor gives a line pull signal to the searching diver, who then lets out more line and repeats the sweeps in ever-widening circles until the object is located or the circles become too large for effective use of the line. The anchored end of the line can then be moved in a predetermined direction and the search repeated. The areas being searched should overlap each other somewhat to ensure that the entire area is searched. The amount of line let out on each circle should be about 1/2 to 3/4 the lateral visibility distance. Another method that can be used to keep the divers together is to use an anchor, stake, or weighted object as a central pivot point. The divers swim a given distance from the pivot point and make a circular sweep completely around that point. The search line must remain taut throughout the sweep. If the object is not located, a length of line is played out (depending on the visibility) and a second complete circular sweep is made. Subsequent sweeps of increasingly larger circles may be made. In limited visibility it may be necessary to lay a reference line. Each time the circling divers encounter the reference line, they expand the pattern by an appropriate distance. If visibility is extremely poor, the diver may have to gently sweep the bottom with his/her free hand using an arc motion to feel for the object. In such situations it is preferable to have the inside diver perform the search, and the outside diver holding the reel swims above the search diver and slightly outside to monitor movement and bubbles. Often, on a silty bottom, the outside diver commands a reasonably good view of the search diver using this technique. Although the tech- FIGURE 9-3. EXPANDING BOX PATTERN SEARCH. FIGURE 9-4. CIRCULAR SEARCH PATTERN.
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