very expensive, leaks around seals of the 

 TPS were common and the complexity of the 

 control system for six degrees of freedom 

 was beyond human capability and required a 

 computer (11). 



Varivec Propulsion System 



The Varivec (variable vector) propulsion 

 system was designed by Westinghouse for 

 DS-20000, but never saw application since 

 the vehicle was never built. A stern- 

 mounted, variable pitch, three-bladed propel- 

 ler (looking somewhat like a single TPS com- 

 ponent, but with three blades instead of six) 

 provides variable thrust from full ahead 

 through zero to full astern by means of col- 

 lective blade pitch control. Through cyclic 

 pitch control a side thrust vector can be 

 achieved to produce yaw directional control 

 through 360 degrees (12). 



Such are the actual and proposed devices 

 that propel submersibles; in addition, the 

 screw-type propeller is generally reversible, 

 it can be varied in speed, and, as will be 

 shown later, can also be oriented (trained) in 

 different directions. 



While submersible propulsion systems do 

 not lend themselves to logical or systematic 

 classification, they can be broken down be- 

 tween: Main Propulsion and Thruster. 



Main Propulsion designates those propul- 

 sion devices on a submersible used primarily 

 to provide forward thrust motion and for 

 cruising. Main propulsion motors are usually 

 more powerful than thruster motors. They 

 may consist of the more classical arrange- 

 ment — one or two stern-mounted propel- 

 lers — or of paired port/starboard propellers 

 mounted amidships on the vehicle. The ma- 

 jority of main propulsion motors are fixed; 

 that is, unlike an outboard motor, they can- 

 not be aimed left or right. Those that can be 

 moved to vary their thrust angle are re- 

 ferred to as "trainable." 



Thrusters are those propulsion devices 

 used primarily to move the vehicle left or 

 right and up or down; they can provide this 

 service while the vehicle is in motion or 

 stationary. Thrusters are generally lower 

 powered than main propulsion motors, and 

 they are usually, but not always, mounted 

 fore and aft. Thrusters may be so located and 

 so oriented as to provide yaw or sidle motion, 



heave and pitch motion or, by being rotata- 

 ble through a full 360 degrees, any combina- 

 tion of motions. While these terms do not 

 mean exactly the same thing to all submers- 

 ible builders, they are generally accepted 

 throughout the industry. 



Dive Planes, Rudders, Stabilizers 



For maneuvering while underway, many 

 submersibles are equipped with rudders 

 (yaw control) and/or dive planes (pitch con- 

 trol), or both. A great number have neither 

 dive planes nor rudders, but rely on propul- 

 sion motors to perform these maneuvers. To 

 stabilize the moving vehicle a fixed fin or 

 dive plane is sometimes attached or molded 

 into the fairing. 



Rudders produce force as follows: When 

 the rudder is deflected to an angle of attack 

 to the flow a force results. This resultant 

 force may be broken into two components, 

 one of which is parallel and the other normal 

 to the direction of flow. Planes produce force 

 in a similar manner. The parallel component 

 is called the drag while the normal or effec- 

 tive steering component is called the lift. The 

 lift of a rudder or plane is influenced by its 

 area, area orientation and rudder angle; rud- 

 der configuration has less influence. Lift of 

 rudders or planes varies considerably with, 

 what is called, the aspect ratio. Aspect ratio 

 is the ratio of the rudder's depth (span) to its 

 width (chord), the latter being the dimension 

 in the direction of water flow. For rudder or 

 plane shapes other than rectangular the as- 

 pect ratio is the ratio of the square of the 

 span to the lateral area. The turning effec- 

 tiveness of rudders varies considerably with 

 aspect ratio. The greater the aspect ratio, 

 the higher the lift for a given rudder deflec- 

 tion. However, with a larger aspect ratio, the 

 rudder will "stall" (lose lift) at a smaller 

 angle. 



The size and configuration of rudders and 

 planes on submersibles is determined mainly 

 by trial and error. Mr. Frank Cunningham, 

 Design Engineer for Perry Submarine Build- 

 ers, uses a rule-of-thumb that the rudder 

 area should be at least as large as the area of 

 the main propeller (about 2 ft^), with the 

 dive planes equal to the rudder in size and 

 shape (rectangular). Earlier Perry vehicles 

 had the planes leading the bow, but because 



377 



