Page 45 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

24 Maritime Archaeology: A Technical Handbook, Second Edition
comparison. It is also worth noting that in spite of all the high-technology equipment that has been used over the years by maritime archaeologists, the majority of archaeological wreck sites have been found by chance, often by fishermen or sponge divers. A great deal of time, effort, and equipment can go into looking for a wreck site, but there are two essential components to conducting a successful survey: appropriate initial research must be carried out prior to the survey and the survey must be conducted in a sys- tematic manner. Without this, a survey will most likely be a complete waste of time. So often searches have been conducted on totally illogical and unscientific principles, based simply on the idea that the site “ought” to be in a particular place (see, for example, Mathewson, 1986, in the search for the Atocha). This is not, one would have thought, how a commercial oper- ation should work nor is it how a scientific archaeological project should be carried out.
II. POSITION FIXING
A. GENERAL CONSIDERATIONS
Two situations exist where it is necessary to locate a position at sea. The first is where a particular site has been located and its position needs to be determined accurately for future relocation. To locate the site as accurately as possible, a large number of position fixes should be taken because of the many small movements a boat makes as it rides over the site. The other situation is where one is moving over the surface of the water or through the water, for example, towing some form of search detector system. Here the search path needs to be known to ensure that the survey is providing adequate coverage. In this moving situation, position needs to be deter- mined rapidly in order to keep pace with the survey, but extreme accuracy may not be necessary. A variety of means of fixing a position are available, ranging from the simplest technique, without any equipment, to the more sophisticated, electronic GPS systems with a data logger and track plotter.
B. TRANSITS
A transit is the visual coincidence or alignment of two fixed features sep- arated by a distance. This coincidence then provides the observer with a bearing or fixed line. By using two or more sets of transits, the coincidence of the bearings can be used to define a position precisely (Figure 3.1). While transits have largely been superseded by the GPS, in many cases earlier