shown in Figure 8.23. A scheme using hyd- 

 raulic motors in lieu of direct electrical drive 

 in MAKAKAI was because only one electronic 

 control circuit would be required to control 

 both motors; hence, simplicity. In NEMO, 

 because the anchor winch only operated with 

 hydraulic power, it was considered expedient 

 to operate the remaining components with 

 the same hydraulic motor. Use of hydraulic 

 motors for propulsion is not common in past 

 or present submersibles, and their employ- 

 ment is generally based on design or space 

 constraints peculiar to a specific vehicle. 



DRAG FORCES 



So far, only the forces that move a sub- 

 mersible have been discussed. In order to 



derive the propulsive power required to 

 move a particular vehicle, the forces acting 

 to resist movement must also be considered. 

 Two forces act to restrain a submersible's 

 movement underwater: Form drag and fric- 

 tion drag between the water and its skin. 

 Quite simply, form drag is created as the 

 water is moved outward to make room for 

 the body and is a function of cross-sectional 

 area and shape. Friction drag is created by 

 the frictional forces between the skin (fair- 

 ings and appurtenances) and the water. 



Form Drag 



The ideal hydrodynamic shape for an un- 

 derwater vehicle is a streamlined body of 

 revolution with a single screw on the center- 

 line as shown in the ALBACORE -type hull 



FLUID 

 RESERVOIR 



ELECTRIC MOTOR 



120 VDC 



lOSHP 



1r^ 



> 



l^ 



HYD PUMP 

 PRESS COMP 



_r^ 



y\ 



m 



FOUR-WAY 

 CONTROL VALVE 



SHAFT POSITION 

 ENCODER 



± 



cv 



m. 



THRUST DIRECTION 

 ACTUATOR 



CV 



T 



HYD MTR 

 4 HP 



POWER OUT TO 

 SPEED REDUCER 



II i CAW 



1 m SHAFT 



; T (SPEED! 



I 



L^^ 



I 



I — r 

 I I 



CAM PLATE 

 ENCODER 

 FEEDBACK) 



ELECTRONIC 



CONTROL 



CIRCUITRY 



r 



CV 



OPERATOR CONTROL INPUT 



^ 



HYD MTR 

 4-HP 



I POWER OUT TO 

 SPEED REDUCER 



L_. 



CV 



iHiy 



THRUST DIRECTION 

 ACTUATOR 



Fig. 8.23 MAKAKAI's electro-hydraulic propulsion system. 

 392 



