Page 72 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 3: Search and Survey 51
encounters or hears of searches that are carried out totally at random and without any recording of the area covered. The result is a waste of time. Before any type of search is undertaken, a number of factors need to be determined: most important is what sort of site is one looking for, what is known of the background information to the loss, and what does one know about the general locality (see Chapter 2 Research above). With some idea of these parameters it is possible to design a search plan which will define the area to be searched, the width of coverage of the search, the type and size of the object being searched for, and the velocity of search. These factors will indicate how long the search will take and thus its feasibility. For example, if a 1-km square area has to be searched for a large object in 10-m lanes at 5 km per hour, that will take about 20 hours and is thus quite a reasonable short-period survey (provided one is not somewhere like the White Sea in the middle of winter). A 10-km square being searched for a small object with 5-m lanes at 5 km per hour will take 400 hours, which is totally different and a major undertaking. Obviously, background research and study of the area will indicate the extent of the area to be searched. The search technique and the type of object or objects being looked for will decide the pattern of search system, the lane width, and the speed of oper- ation. It is also prudent to build a large safety factor into the detection range, since it is better to ensure adequate coverage than have to repeat the survey. Even with quite simple searches, some method of recording the path of the search is essential. Often an initial enthusiasm leads to false optimism in the belief that the objective will be quickly and easily achieved. However, all too often the grim reality subsequently sets in when the site is not found. At this point, unless an accurate record has been made, it will be necessary to start all over again; this time in a more systematic manner. Naturally the GPS is a major factor in the operation of a search. Diver- operated GPS has been used for some time, particularly in shallow water. In these cases the hand-held instrument is usually encased in a water-tight container which the diver holds, and its antenna floats on the surface con- nected to the GPS by an aerial extension cord. Another option is towing divers behind a boat and recording the track of the boat and the position of the diver. This can be done knowing the layback (see Figure 3.28 below).
B. SWIM-LINE
Any visual search technique requires a record of what area has been searched and what areas are still to be searched. Thus, it is of the utmost importance that the position of the diver or divers can be located at the surface and thus plotted on a chart. This is best done using a buoy on a line attached to the diver and a small boat can be used to plot the position of