Project Mohole Drilling Platform 



Each positioning unit is now assigned a longitudinal component of thrust 

 ^x- ^p/^ - '^reqd/'^j Where the plus sign applies to the starboard hull and the mi- 

 nus sign to the port hull. Each unit is assigned a lateral component of thrust 

 F = F J /6 . The total thrust assigned for each unit is the vector sum of the 



y y redq ° 



components and the angle of train is determined from the components. 



Thrust Produced 



The main propellers produce the thrust F^ up to the limit of 240,000 pounds 

 forward or 120,000 pounds astern. 



The thrust produced by each positioning unit is calculated separately as 

 described below. The positioning computer actually controls rpm rather than 

 thrust, whereas the thrust obtained depends not only on the rpm, but also on the 

 local velocity of the water relative to the unit. 



First the total thrust required from the unit is limited to 25,400 pounds. 

 Then the thrust obtained is calculated as 



f"obt = ^ask " 1-075 (1+ 0.0313 V -0.0696 V cos 6) 

 where 



F^^^ = thrust obtained 

 ^ask - thrust required 



V = absolute value of relative water velocity 



6 = angle between water velocity vector and thrust vector. 



NUMERICAL VALUES 



Numerical values of the constants can be varied as program input data. 

 Typical values as derived from analysis of test data are given below. It will be 

 noted that the dimensions Lj through Lj do not correspond to actual hull dimen- 

 sions but to an idealized equivalent cylinder. 



Lateral spacing of hulls, feet 

 Longitudinal spacing of columns, feet 

 Lower hull diameter, feet 

 Column diameter, feet 

 Displacement at 65 ft draft, L tons 

 Vessel mass, slugs 

 All, slugs 

 A22, slugs 

 A26, slug-feet 

 Age. slug-feet 



441 



