48 



AUTRANAV MK3 System - The AUTRANAV system is used by ULS Marine Ltd. The 

 system can be bottom-oriented or surface-oriented, the following description 

 applies to its bottom-oriented application. 



In the basic installation three transponders are deployed approximately 4m 

 (13 ft) above the seabed and approximately 1km (0.6nm) apart in a triangle. 

 Approximate coordinates are taken for each transponder location and an accurate 

 local measurement of sea water sound speed is also made. A calibration survey 

 is then run in a cloverleaf pattern during which a number of interrogations 

 are made from locations within the grid. The results are stored in memory, 

 from these the actual relative transponder co-ordinates are computed and plotted. 



The AUTRANAV system used with CETUS requires a fish transponder to be streamed 

 from the survey ship. Provision must be made on the ship for the launch and 

 recovery of the transponders and fish. The bottom-mounted or Long-Base- Line 

 system is the most accurate (^Sm) , but the work area is limited to within 

 the vicinity of the transponder array. Should the work point move outside 

 this area these transponders will require re-surveying. 



2.1.13.b Surface-Oriented Systems 



This category includes systems which provide position fixes of the submerged 

 vehicle relative to the surface support ship, rather than to bottom-mounted 

 references. Four systems are in use: RS-7, RS/902 and RS/904, Digital 

 Acoustic Position Reference System (Honeywell, Marine Systems Division, Seattle, 

 Washington) ; AMF Model 301 Range/Bearing Acoustic Relocator (AMF Electrical 

 Products Development Division, Herndon, Virginia) ; Wesmar SS210S Sonar Tracking 

 System (Wesmar Marine Systems Division, Seattle, Washington) ; AUTRANAV MK3 

 (Polytechnic Marine Ltd. , Daventry, Northants) . 



RS-7 System - The RS-7 system is used by Hunting Surveys Ltd., Ocean Systems 

 Inc. , Martech International, Taylor Diving and Salvage Co. , and the Harbor 

 Branch Foundation. The system consists of shipboard and subsea components. 

 Shipboard components include: an operator's display and control cabinet 

 (permits selection of operational modes, performs signal processing, and displays 

 position coordination), and a vertical reference unit (measures ship's pitch 

 and roll) . The subsea component is a hydrophone in which a miniaturized array 

 necessary for system functions is incorporated. 



ROV components consist of a miniature position reference beacon and a depth 

 sensor. A standard position reference beacon is installed on the bottom or on 

 a wellhead or whatever might be an appropriate reference point. The system 

 can and does work without a bottom reference beacon, for this reason the RS-7 

 and its successors (RS/902 and 904) are placed in the surface-oriented category. 



Initially the bottom or hardware-mounted beacon is acquired by the shipboard 

 hydrophone and displayed on a CRT in the display /control cabinet. When the 

 ROV has submerged its beacon also appears on the CRT (as a different symbol) . 

 The support ship views the position of the ROV with respect to the wellhead 

 beacon and maneuvers the ship to keep the submersible within the desired tether 

 distance . 



