McClure and Hove 

 where 



X = the eastward displacement of the vessel from the hole 

 Y = the northward displacement of the vessel from the hole 

 Xg = the apparent eastward displacement 

 Yg = the apparent northward displacement. 

 The apparent bearing of the hole with respect to the vessel is given by 



6 = arctan (Y^/Xg) - "V + 180° 



where w = the heading of the vessel, measured counterclockwise from east. 



Required Translational Thrust 



The required translational thrust is computed as follows: If d > 50 feet, 



Freqd = l^^O D - 37,500 ; 



otherwise, F^^^ = 0. D is the apparent distance to the hole. 

 The longitudinal and lateral components are 



^xreqd"^reqd ^°^ ^ ' longltudinal thrust, positive forward, 

 ^yreqd = ^reqd ^^^ ^ = lateral thrust, positive to port. 



There is no upper limit on F^.^ . as such. 



Required Turning Thrust 



The heading error is given by Aw = "Pq - l*, where ^^ is the ordered heading. 

 Heading is controlled by thrusting ahead with the positioning units on one hull 

 while thrusting astern the same amount with the positioning units on the other 

 hull. The main propellers are not used to control heading. The required thrust 

 per hull is computed as follows: 



If |aw| > 3°, M^g J = 40,000 sin (A>i')/sin (30°), but not more than 40,000 

 pounds. 



Assignment of Thrust to Various Units 



" freqd > 36,000 pounds, F, = 0.6F,,,qd and F^ = 0.4F^^^^^; otherwise, 

 F^ = and Fp = F^^p .; where F^ is the thrust assigned to the main propellers 

 and Fp is the total longitudinal thrust assigned to the six positioning units. 



440 



