Page 58 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 3: Search and Survey 37
receiving angles. In resection 1 the fix is excellent, whereas in resection 2 there is no fix at all because all three position circles coincide and the posi- tion could exist anywhere on that circle. In resection 3 the receiving angle BCD is very small, yet the fix is good, because the position angles cut at a good angle. In resection 4, two of the position circles are close together, and a small error in BDC will have a large effect on the position of D, thus making it a poor fix. In resection 5 the fix is good, but care must be taken to ensure that the fix is not approaching a circular fix as in resection 2. Finally resection 6 is a good fix provided that the smallest angle subtended by the three marks at D is not too small.
One looks back nostalgically to the days of sextant survey work. Espe- cially in a small open boat during relocation of a site, with the operator driving the boat with one hand while holding the sextant, set at the correct angle, in the other, and thus maintaining the correct course (Figure 3.9). As the fix was approached the other operator would be calling “left hand down a bit, no, too far, back a bit,” and so on. As one can imagine, it was of para- mount importance when conducting a sextant survey to establish an atmos- phere of good-natured cooperation, otherwise the whole operation could end in violence.
Figure 3.9 Operating a sounding sextant at sea.