60 



Cable burial vehicles employ essentially the same techniques and instrumentation 

 as do the trenching vehicles. Vickers SEACAT is an exception, in that control 

 of the vehicle is not by remote means, but is performed in situ by 

 divers or a manned submersible. In this respect SEACAT does truly fall into 

 the category of a remotely controlled vehicle. 



The general purpose vehicles are more akin to the free- swimming, tethered 

 ROVs . SEABUG I, for example, has CCTV, two manipulators, an echo sounder, 

 side scan sonar, directional gyro, depth gage and pitch/roll indicator. The 

 vehicle can also accommodate tools for cable burial (jetting) or for various 

 manipulative tasks, such as cutting, grinding, brushing, etc. 



The TRAMP system is one of the more sophisticated bottom-crawling vehicles. 

 Repetitive tool operations with continuous rate changes, for example, can 

 be tape-controlled and the CCTV image is 3-dimensional and reflects vehicle 

 tool arm movements, roll and pitch, front and rear axle angles and wheel 

 speeds. The display/control console of the TRAMP system is guite similar 

 to those of the more complex, tethered, free-swimming vehicles. 



2.2.8 Navigation 



Navigation of pipeline trenching vehicles is relatively simple since the 

 position of the pipe is known prior to the operation and the position require- 

 ments call for no more than knowing where the device is as it proceeds along 

 the pipe. This information can be obtained by a single surface-oriented 

 acoustic tracking system or by CCTV which can be used to observe field joints 

 on the pipeline. Geodetic positioning is supplied by the support barge which 

 is moored over the device and periodically re-positioned as the trencher moves 

 along the pipe. Similar techniques are employed by cable burial devices. 



Since the bulldozing devices operate in shallow water, visual navigation 

 techniques are often used. The JH160 vehicles, for example, support a mast 

 that protrudes above the water surface which is configured and marked to show 

 the direction and depth of the vehicle and the blade position. The operator, 

 who is either on a barge or on the shore, maneuvers the bulldozer (with 

 radio signal transmission or hardwire) by visually observing the mast orientation. 

 For deep water work, where the mast approach is not feasible, a bottom-oriented 

 transponder system (see Section 2. 1.13. a) is used. 



Since the general purpose vehicles are wider- ranging and their tracks are 

 less predictable, they employ systems similar to the free-swimming vehicles. 

 Visual sighting and magnetic compasses with directional gyros are common. 

 Bottom-oriented and surface oriented positioning systems are also capabilities 

 found on the general purpose vehicles. SEABUG I, for example, employs the RS/904 

 surface-oriented system, but is also capable of using the ATNAV bottom-oriented 

 system. 



2.2.9 Support Ship Components/Requirements 



The wide variation in bottom-crawling vehicle size and mass guite naturally 

 results in a v/ide variety of support ship components and requirements. Unlike 

 the tethered, free-swimming vehicles, operators of bottom-crawling vehicles - 

 particularly the trenching vehicle operators - do not speak of ships of 



