Project Mohole Drilling Platform 



POSITIONING COMPUTER SUBSYSTEM 



The Positioning Computer Subsystem is a dual-channel electromechanical 

 analog computer which accepts range information from the three reference sub- 

 systems, computes vessel position with respect to the drill hole, and generates 

 orders for the vessel power units. 



Operation of a single channel may be explained as follows: 



The Reference System Selector is used to select range data from one of the 

 three reference systems for computation, and the Reference Point Selector is 

 used to select two or three of the four reference points for computation. Using 

 the selected range information, the X-Y Distance Computer computes the dis- 

 tance between the vessel and a coordinate center in X-Y coordinates. The Geo- 

 graphic to True Coordinate Converter then rotates these coordinates to a true 

 north coordinate system. Parallax Offset between the Long Baseline Sonar 

 transducer and the center of the vessel, and Coordinate Center Offset between 

 the coordinate center and the drill hole are then added by Offset Addition. The 

 resulting composite signal represents north and east distances from the vessel 

 to the drill hole. 



The composite signal is routed to total Range to Hole, North Range to Hole, 

 and East Range to Hole indicators and to the Vessel Position Display. This dis- 

 play also accepts a gyrocompass input for displaying vessel heading as well as 

 vessel position. 



The composite signal is also sent through the Set Point Offset Integrator, 

 which may be used to automatically generate set point offset signals. These 

 signals are used to generate thrust requirements in the Fore -Aft Positioning 

 Thrust Computer and the Port-Stbd. Positioning Thrust Computer. 



Main propulsion motor thrust requirements are scaled from total fore -aft 

 thrust requirements and subtracted from this signal. Ordered Heading, gyro- 

 compass information and fore-aft thrust requirements are combined in Vessel 

 Heading addition circuits to generate required vessel turning force signals. 

 Positioning unit orders are generated in the Port Pos. Unit Thrust and Azimuth 

 Computer and in the Stbd. Pos. Unit Thrust and Azimuth Computer. 



Computed quantities from computer channel A and channel B are compared 

 at several points. Alarms are associated with each comparison to indicate that 

 a difference exists. Only one channel is used for vessel control and position 

 display at one time. 



MOTOR CONTROL SUBSYSTEM 



The motor control subsystem consists of servo modules and electronic cir- 

 cuitry necessary to control the main propulsion motors and the positioning units. 



Propulsion unit control orders are available from either computer channel. 

 In addition, these orders are routed through Mode Select circuits for selection 



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