15. After the FOA engineer outlines the objectives of the survey with 

 the captain, crewman, and manufacturer's representative, the representative 

 gives a brief explanation of how an SSS works. The crewman and the represen- 

 tative load and set up the equipment while the engineer discusses the course 

 to be navigated with the captain. As the captain begins a practice run on the 

 course, the representative assists the engineer as he performs checks and 

 makes initial settings on the control unit, then helps the crewman deploy the 

 fish. During the practice run, SSS images are produced and various range and 

 gain settings, etc. are tried, in addition to testing the dual -frequency tow- 

 fish option (100 and 500 kHz) . Having already sailed the most difficult parts 

 of the course in the relatively rough waters that day, the captain returns to 

 the marina. On the return trip the engineer notes that recreational fishing 

 boats could present an access problem. 



16. Plans are made for primary and alternate survey dates. Prior to 

 the survey dates, the engineer, with camera and film, arranges to have the 

 crewman meet him earlier on the morning of the survey to set up the onshore 

 components of the positioning system. Based on a review of the marine fore- 

 cast on the afternoon before the chosen date, the decision is made to go 

 ahead. 



17. Weather conditions on the survey date include a moderate steady 

 wind, a 5-ft swell, and 2- ft waves. Although the wave/swell conditions are at 

 the borderline of acceptability for this shallow-water inspection, all other 

 conditions are good and the captain feels that the agreed-upon course can be 

 navigated. The crabwise motion of the boat due to wind poses no problem, 

 since the electronic positioning will be used and the crewman will be noting 

 towfish position relative to the boat. 



18. The first pass parallel to the breakwater is carried out at a 

 steady speed of 5 knots in water averaging 35 ft in depth; the towfish is 

 "flying" at an average altitude of 20 ft above the bottom. The 100-kHz fre- 

 quency with a range selection of 100 meters has been selected for the initial 

 pass. The above-water portion of the breakwater is at an average distance of 

 150 ft from the boat. Well within the backscatter limit at this range, there 

 is good resolution with the 100-kHz frequency that tolerates the wave -induced 

 towfish motion better than the 500 -kHz frequency. 



19. While preparing to make a second parallel pass to look up at the 

 structure from the relatively low towfish altitude of 10 ft (above the bottom) 



10 



