4,500 pounds and 20,000 pounds, respectively, for 100-ton and 600-ton 

 loads. Unlike bottom crawling vehicles, submersibles will stir-up bottom 

 sediments only slightly. They are also far less susceptible than bottom 

 crawlers to becoming stuck in areas where soft, pelagic sediments predominate. 



The second role, that of observer and relayer of position corrections 

 to a surface based positioning system, i.e., dynamically positioned ship or 

 platform, is probably a more feasible role for a deep diving submersible. An 

 acoustic load targeting system patterned after the one developed by AC 

 Electronics Corporation for drill hole reentry could serve as the prime load 

 positioning subsystem with a submersible (which could be any one of several 

 boats currently available with depth limits in excess of 6,000 feet) serving as 

 a backup in the event of failure of the prime acoustic targeting system. 



Displacement/Rotation of Surface Craft 



The first step in lifting or lowering a load will be to determine the 

 location of the surface vessel on the ocean. This obvious prerequisite for a 

 successful operation implies that the vessel will be equipped with some 

 advanced positioning and navigational systems which could be used to 

 position the load on the bottom. 



It is predicted with some confidence that dynamic positioning will 

 be the most suitable system for maintaining surface position. The primary 

 data needed in a dynamic positioning system are the relative positions of the 

 surface craft and various points on the ocean floor. The more advanced 

 systems are able to maintain a vessel's position over one point within fairly 

 restrictive tolerances. In the case of the heavy-lift system, the relative 

 positions of the load and ship, in addition to the relative positions of the 

 load and a reference point on the bottom, would be required data inputs. 

 An automated positioning system could provide commands to the position- 

 ing propellers to maneuver the ship into a position where the load could be 

 placed on the desired spot. This system would work for both cable and pipe 

 string suspension systems and would require only a slight modification to the 

 command systems presently used for dynamic positioning. Figure 15 

 illustrates the arrangement of the components. A reference sonar beacon 

 would have to be placed on the load, but this would probably be standard 

 equipment for most ocean bottom installations. Assuming steady state 

 conditions, a load could probably be placed within a circle of radius 1 to 2% 

 of the water depth. For most near-term underwater installations this 

 tolerance may be acceptable. 



