The success of the GLOMAR CHALLENGER'S dynamic positioning 

 system serves as strong testimony to the desirability of having the same type 

 of system on the heavy-lift vessel. Dynamic positioning systems are easier to 

 use, faster, and require none of the auxiliary vessels necessary for conventional 

 anchoring techniques. Moreover, conventional anchoring techniques are 

 depth limited, thereby seriously restricting the chances of extending the 

 depths to which the loads can be lowered and positioned. 



POSITION LOCATION'S 



A problem related to maintaining position is that of positioning the 

 vessel at the proper location (as opposed to simply holding position). It 

 appears that the accuracy of the positioning operation is inversely related to 

 the vessel's distance from land. For example, visual fixes on a land-based 

 object 5 miles away, possibly by the use of a sextant, will permit positioning 

 to within ± 5 to 15 feet. For distances from 5 to 300 nautical miles from 

 land, a surface craft can be positioned to within ±30 to 50 feet; however, 

 accuracies in this range are possible only with sophisticated receivers on 

 board the vessel and elaborate shore-based transmitters. In areas more than 

 300 miles from land, it appears that accuracies can vary from 1 to 5 nautical 

 miles; while this is accurate for navigational purposes, it is unacceptable for 

 underwater construction. 



At first glance it would appear that the limitations of present 

 positioning technology would seriously inhibit underwater placement and 

 recovery. However, this is not as severe a limitation as one would suppose; 

 Table A-2 illustrates why this is true. 



Table A-2. Average Distances From Land to Selected Depths 



(Source: NCEL TR-597: Deep ocean power systems, by E. Giorgi. 

 Sept. 1968) 



Location 



Average Number of Miles to Reach a Depth of — 



600 ft 



2,000 ft 



6,000 ft 



East Coast 

 West Coast 



70 

 21 



150 

 28 



175 

 32 



100 



