Project Mohole Drilling Platform 



necessarily represent expected sea conditions in the Hawaiian area. Design 

 limiting conditions are simultaneous winds of 33 knots and current of 3 knots 

 with commensurate seas. This results in enough power so that squalls of much 

 greater intensity can be withstood in combination with nominal ocean current. 



Two propulsion systems are provided: The main propulsion system con- 

 sists of a propeller at the stern of each lower hull powered by a 7500-HP DC 

 motor. The positioning propulsion system consists of six right-angle drive 

 units, one in each of the six main columns. These units each consist of a 5 ft 

 9 in. shrouded propeller driven through right-angle gearing by a 1000-HP DC 

 motor. The propellers are trainable and can be continuously rotated in either 

 direction to provide thrust at any desired angle. Both the main propulsion and 

 the positioning propulsion systems are controlled automatically in the station- 

 keeping mode. 



The positioning system includes a position reference system which deter- 

 mines location relative to the hole by sonar ranging to bottom -mounted trans- 

 ponders. A positioning computer calculates the relative platform position, de- 

 termines the thrust required to correct position errors, and directs the 

 propellers accordingly. Two identical computers are installed to insure a high 

 degree of reliability. These systems are explained in more detail in Appendix 

 D. A semiautomatic mode is also provided in which the positioning units are 

 coupled to a joy-stick. 



In moving from one site to another the platform will be operated at light 

 draft, with the lower hulls on the surface. Since ample propulsive power is 

 available as a result of positioning requirements, the platform will be operated 

 self-propelled in transit. In this mode it will operate very much like a ship in 

 straight and curved maneuvers. No rudders are provided, only the main pro- 

 pellers will be used, controlled manually from a console on the bridge either at 

 the same speed for straight line travel or at different speeds to develop turning 

 moment. 



It can be seen that propulsive power, rotation, and resistance in all direc- 

 tions are of interest. As an essential step in design of propulsion and control 

 systems, it was necessary to determine characteristics of the platform in 

 straight-line motion fore and aft, athwartships, and obliquely to the center line 

 and in curved maneuvers varying from turning about its own vertical center line 

 to turns at normal turning radius. These characteristics were required at the 

 normal drilling draft of 65 ft, and at the light or transit draft of about 29 ft. 

 Since the analysis and test procedures differ between the deep draft and light 

 draft conditions, these are treated separately. The most vital criterion of the 

 drilling platform is that it must remain on station within the prescribed limits. 

 This facet of operation received the most attention and is discussed first and in 

 most detail. 



STATION-KEEPING 



In order to verify the platform's ability to hold station, the resistance and 

 moment data were combined with the propulsion data in a comprehensive math- 

 ematical model for single plane performance. The mathematical route was 



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