Project Mohole Drilling Platform 



trim tabs since in respect to other criteria they result in a slight improvement. 

 In any event, the overshoot angles are somewhat less than those usually encoun- 

 tered in conventional ships and it may be concluded that controllability of the 

 platform as designed is good. Other measures of controllability are the reach 

 (time required for the vessel to return to its original base course at the end of 

 the first half cycle), and the period (time to complete a full cycle). Small values 

 of these parameters are usually associated with good controllability. Results of 

 the tests show that reach is 335 seconds and the period 660 seconds. These val- 

 ues are in the same order as those encountered in ship hulls and are considered 

 indicative of satisfactory maneuvering performance. Speed during these tests 

 was nine to ten knots which is the range of speeds expected during transit from 

 one site to another. 



In addition to the self-propelled maneuvering tests, towing tests and wind 

 tunnel tests at the University of Michigan Naval Tank and the David Taylor 

 Model Basin provided information on resistance, side force, and moment due to 

 wind, current and drift angle which must be resisted to maintain course. The 

 installed main propulsion power of 7500 HP per shaft provides ample margin 

 for headway and steering control during transit. Figure 13 is a curve of resist- 

 ance versus speed at the 29-ft draft. It incorporates a 25 percent allowance 

 over model test extrapolations for appendages and roughness. Superimposed on 

 this is an approximate propeller thrust curve showing the speed which can be 

 attained at full power, or 7500 HP per shaft. It will be noted that the positioning 

 units will be retracted during long transit periods to reduce drag. Positioning 

 unit propeller characteristics are such that they cannot be used effectively at 

 the higher speeds required during transit conditions. 



2 4 6 8 10 



PLATFORM SPEED, KNOTS 



10 20 30 40 50 60 70 



WIND VELOCITY 



Fig. 13 - Platform re- 

 sistance and thrust at 

 29 ft transit draft 



Fig. 14 - Transit speed 

 vs head wind 



429 



