53 



Two CRT display modes are possible: A-Scan and B-Scan. The A-Scan mode 

 displays a horizontal line across the CRT screen. The vehicle is displayed 

 as a spike on the line whose position provides range to the vehicle. In the 

 B-Scan mode (which is the normal mode for navigation) a PPI presentation is 

 provided which is similar to search radar. 



The vehicle is displayed as a blip on the CRT from which range and relative 

 bearing (to the ship) can be obtained. The following specifications apply 

 to the SS210S system. 



Maximum Range: 1,000m (3,280 ft) active/sonar mode, 2,000m (6,560 ft) 



passive/transpond mode. 

 Frequency: 160 kHz active mode, 25 kHz transponder interrogation (passive) 



mode 

 Operating Voltages: 12, 24, 32 VDC, 110 VAC, 60 Hz 

 Transmitter Power Output: 2,000 watts peak-to-peak 

 Transducer Beam Width: 7 degrees 



Sector Scanning: Switched in steps from 30 degrees to 360 degrees 

 Target Lock-on: Automatic tracking of a vehicle without operator control 



is a feature of the system 



AUTRANAV hJK 3 - This system is used by ULS Marine Ltd, The following describes 

 the procedures this company employes to track their CETUS vehicle. 



One transponder is suspended from the bow, another from the stern;, both are 

 approximately 5m (16 ft) below the surface. A fish transponder is streamed 

 from the surface ship and slant range to the vehicle is calculated by noting 

 the round trip time for a pulse to travel from the fish to a vehicle-mounted 

 transponder and back to the bow and stern transducers. The angular bearing 

 can be derived from the time difference of the transponder replies. Adequate 

 means must be available to secure the forward and aft transducers and launch, 

 stream and recover the fish. The system's work area is limited to within 

 500m (1640 ft) of the support ship, the accuracy is approximately 3m (10 ft) . 



The preceding discussion describes the various navigation systems as they 

 are manufactured. In some instances the operators have modified these systems 

 to satisfy their particular navigational requirements, in other instances 

 they have designed their own system with components purchased individually 

 from various suppliers. Sub Sea Surveys Ltd., for example, interrogates 

 a vehicle-mounted transponder by sending an electrical pulse down the umbilical 

 cable. The transponder signal is sent thru-water and received by two transducers 

 on the surface ship to provide slant range. Phase variation between the two 

 transponders is measured to provide bearing to the vehicle relative to the 

 ship's heading. Some work tasks, such as pipeline "as laid" surveying, make 

 it desirable to obtain the geodetic position of the vehicle as it progresses. In 

 this instance Sub Sea Surveys has devised a technique where ROV range, bearing 

 and depth and the ship's heading and position (determined by a surface electronic 

 positioning system, such as Hi-fix, Pulse 8, Satnav, etc.) is fed via a 

 specially developed interface unit into a PDP II computer system. A navigation 

 program converts the data into UTM coordinates which provides the vehicle's 

 position and, hence, the pipeline position. 



