67 



up-down motion, the fish now undergoes an alternating fast-slow surge motion 

 in concert with the depressor's up-down motion. The forward surge can be so 

 great as to produce a blur on the TV monitor which seriously detracts from 

 the quality of the video and still photographs. 



The RUFAS vehicles take a quite different approach to vehicle altitude/depth 

 control. Since they are towed at relatively high speeds (3 to 6 knots) and 

 at relatively shallow depths, dive planes can be used to control vehicle pitch 

 once an appropriate length of cable has been paid out. RUFAS II will also 

 incorporate an automatic terrain- following control system. Altitude infor- 

 mation from a downward- looking echo sounder is used to activate servos which 

 control the two stern dive plane's pitch. 



2.3.7 Instrumentation 



Instrumentation carried by towed vehicles is much the same as that described 

 in Section 2.1.7 regarding tethered, free- swimming ROVs and need not be 

 discussed further. Those areas that differ significantly, however, are mani- 

 pulation, CCTV and in situ analysis. 



Towed vehicles do not carry manipulators simply because they cannot stop 

 to use them. Lacking the capability of self-propulsion, the vehicles must 

 be continuously underway if they are to operate as designed. There are, 

 nonetheless, vehicles which have the capability to collect bottom samples. 

 I-IANKA 01 carried a specially designed suction nozzle which picked up manganese 

 nodules as the vehicle was towed along the bottom. A heavy wire mesh dredge- 

 type sampler is housed on the underside of S^, and the sampler (31cm L x 15cm W 

 25cm H) is lowered and raised between the vehicle's skids by a shipboard- 

 controlled servo system. The present S^ sampler is only capable of single 

 sample retrieval and storage, a multi-sampling system has been designed which 

 permits multi-sample storage in a carousel storage compartment. The Soviet 

 Institute of Oceanology's CRAB is the single exception regarding manipulation. 

 Since CRAB is deployed from a drifting support ship rather than one which 

 is underway, the vehicle can be placed on the bottom and, by maneuvering the 

 support ship to station-keep above CRAB, adequate time is gained in which 

 samples can be retrieved by the vehicle's manipulator. 



Closed circuit television is not as heavily relied upon on towed vehicles 

 as it is on the tethered, free- swimming vehicles. The reasons vary, but 

 essentially reduce to the fact that there is no need for continuous video 

 taping of the bottom. Since the vehicles move at very slow speeds (0.5 to 

 1 knot) , periodic images of the bottom on TV (using strobes as light sources) 

 are adequate. A further consideration involves image resolution of TV. 

 Since resolution of the TV image does not compare in quality with photographic 

 techniques, operators of deeply towed vehicles rely on photography for 

 docuanentation rather than TV. 



2.3.8 Navigation 



Position accuracies acceptable to towed vehicle operators range considerably. 

 Many, if not the majority, do not employ a means of tracking the vehicle itself. 



