Page 225 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

204 Maritime Archaeology: A Technical Handbook, Second Edition
Figure 6.20 An oblique three-dimensional plan of the Tektash site created in the Rhino 3-D graphics package. (Courtesy of Xila Matthews and the Institute of Nautical Archaeology, Bodrum, Turkey.)
lack of visibility under water, it is strongly recommended that every task to be performed under water should first be practiced on land (this is a good idea irrespective of the visibility). Consider, for example, a typical situation of setting up a right angle for a site grid 10 ¥ 10 m. Each task in the process can be rehearsed on land in order to anticipate problems which will be exceedingly difficult to resolve in poor visibility under water. Diver A takes the stakes and the hammer, diver B the tape measure. The point of the corner of the grid needs to be preselected and a guideline to the spot laid beforehand. Diver A hammers in the stake and A and B then go 3 m to set up the start of the 3-4-5 triangle. How do you determine which direction to go? Should a prearranged line be laid or a compass course be used? Would it be better to have a string 3-4-5 triangle rather than a tape? Which is easier? If all these operations can be tried out so that the divers are famil- iar with exactly what they have to do, where they have to go, and what is likely to go wrong in rehearsal, there is a chance that the operation may be a success. In general it is difficult for divers to communicate under water, but it is worth noting that it is possible to talk under water through a reg- ulator, provided you speak slowly and clearly. It should be remembered that Murphy’s law operates with extra efficiency in low visibility, i.e., anything that can go wrong will go wrong and probably in a big way. Certainly under- water communications systems would be of immense benefit here, both for efficiency and safety.