Search and rescue divers follow systematic movement patterns to cover as large an area as possible under different diving conditions. These diving patterns are chosen depending on the distance or area to be covered, the depth to be searched and the type of reef structures present.
Editor’s note: This is the second part of a two part series on search and recovery. Part I discussed planning, equipment and procedures.
The pattern you use is often the least important part of the procedure. The intelligence gathering before you get wet, the safe procedures review and planning the dive are more critical elements.
Table of Contents
Circular search patterns are popular because they are simple and effective. Consider a circular search pattern when there are no obstructions, visibility is reasonably good or when you are trying to snag an object with a line.
One end of a line is attached to a fixed point and becomes the axis. This could be a boulder or a diver. If a diver controls the line at the axis point, he or she turns as the searcher turns so as not to get wrapped in the line like a mummy.
The axis diver lets out a length of line each time the swimmer has finished a complete revolution. The axis diver needs a marker to fix the starting point. A rock or a goody bag lying on the bottom is fine. How much line you let out on each pass depends upon the visibility and the size of the search object. Remember, the searcher’s field of vision is only about three feet unless he or she can scan back and forth. So, do not increase your circle size ten feet on each repetition if you only have a three foot field of vision and you are looking for a wallet. If you are searching for a refrigerator and have ten foot visibility, then scan your viewing area and let out eight feet of line on each revolution. Stay inside your field of vision and overlap a little on the edges to be certain you are not missing the lost object.
If you use a fixed point such as a boulder as the attachment point, then tie onto the boulder and begin your search at the line’s far end. As you circle around the boulder, the line will become shorter naturally and you’ll wind your way toward the center. If the boulder is not big enough to reel in sufficient line, then the searcher may need to take up some line as well.
To search a big area faster, use multiple divers on the search line. Each sweep with three divers on a line could cover 15 feet. As you add divers to a line, however, it becomes harder to keep the line taut and straight, reduces the effectiveness of line pull signals and increases the chances of stirring up the bottom.
Some divers like to tie a knot at their hand-hold positions as they begin each revolution. This creates a marker in case the line slips during a sweep or if sweeps are later repeated at half-intervals to recheck an area.
When moving to the next adjacent search territory, typically the searching diver stops and holds position. The axis diver swims to a new center point. When the line is again taut between the divers, the correct distance has been moved. The searching diver begins the process again, only instead of letting out line on each rotation, the searcher takes in line. Remember, if you run four circular patterns that cover a roughly square area, a little wedge of land is missed between the circles, unless you have overlapped them. It is not practical to go back and search these wedges of missed territory – you won’t be able to find them easily.
The semicircular search is an adaptation of the circular pattern and may be used when obstructions do not permit a full 360 degree sweep. Semicircular searches are useful alongside a dock, shoreline or jetty.
The procedure is similar to a circular search. A line is attached to the center of the search area along the defined straight edge. The searching diver lets out line a little, swims a half-circle, stops, lets out more line, reverses direction and returns to the starting point. The searcher continues this pattern, moving slowly and constantly turning his/her head to scan the bottom. Be careful not to move faster than the range of visibility and use a complete left-right-left head movement. Going too fast is a common mistake.
An adaptation of the semicircular search is used when under an anchored boat. Attach the search line to the anchor, then swim a bit farther to the right and left than the path the boat has covered while it was swinging on its anchor. Successively let out line each time you reach the starting side of the arc until you have covered an area well astern the vessel.
A contour is not a distinct search pattern but a technique that uses the natural lay of the land. The idea is to create a pattern that can be followed successively. For example, if a lost object was thought to be in 40 feet of water on a gradually sloping bottom that featured a series of rock finger reefs parallel to shore, a contour search could be the best choice.
The searchers swim to a fixed depth that is slightly beyond the expected “find zone.” Using the reef structures and depth as markers, the buddies swim along a reef finger a distance that is slightly longer than the prime find zone. At the end of the distance (measured by kicks, breaths or time), the pair makes a 180 degree turn, moves slightly shallower and swims back parallel to the first pass. Successive sweeps are conducted until the prime area has been searched and the lost object found or you conclude you need to search another area. The search can be repeated in an adjacent grid using the same techniques. It is helpful to mark the boundaries of each grid so if you need to search an adjacent grid you do not leave an unsearched strip in between grids. Sleeper’s Law: Unsearched strips between grids contain lost objects.
DEFINED GRID SEARCHES
Scientists use meter square plastic pipe frames to define an area they are observing. Searchers looking for small objects lost on muddy bottoms can use frames to define their search area as well. It could be a plastic frame or four sticks poked in the bottom to define the corners. Wearing heavy gloves, searchers systematically move across the grid, plunging their hands into the mucky bottom trying to feel the small object of the search. Visibility quickly deteriorates and the search continues by feel. Generally, if the object is not found in the first or second grid, the visibility is so wiped out divers need to leave and return later to start on a new grid. If you leave and plan to come back, remember to leave the grid in place so you know where to move it to search new territory.
STRAIGHT LINE SEARCHES
These are used to cover very long distances and may include towing a diver on a planning board or tow bar. This only works at extremely slow speeds (idle on many boats), in excellent visibility or when looking for very large objects. Using a sled takes a great deal of diver and boat operator skill, patience and practice.
Straight line searches often follow a compass course to stay on track. This could be a wrist compass, console or a navigation board. Since maintaining a true compass course heading can be difficult, one diver often navigates and leads, while the other follows and focuses on searching.
One way or two way (return) straight line searches can be used, depending upon the terrain. Straight line searches are often used when nature or man has provided guideposts, such as pier pilings. Rather than swim around each piling, it may make more sense to first swim the length of the outside row and return on the inside. It depends upon visibility and the size of the lost object.
If no natural or manmade guideposts exist, a line weighted on both ends can be positioned on the bottom. Straight line searches are conducted working off either side of the anchored reference line. If the missing object is not found, the line is moved or a second line is added and the entire process starts again. Leapfrogging lines can mark quite a large territory.
The goal of a search is to find the lost object but the overriding concern must be for the safety of the searchers. Many search techniques use two divers who are not in close contact. Searchers need to have a higher degree of diving experience and self-confidence to be comfortable in low visibility, using lines and being out of close contact with their buddy. Nothing is worth finding at the cost of your health or life.
Search and recovery are valuable diving skills. Consider taking an advanced or specialty course from your local dive store or instructor. Reading about searching and actually working underwater with lines are two different things!