d) ^^Water, Air and Interface Vehicles'^ 



(4): Similar to reference (3) in purpose 

 and technical detail, this publication 

 discusses hydrodynamic forces and pro- 

 pulsion for airborne and waterborne ve- 

 hicles on a common plane. 



e) "Principles of Naval Architecture'' (5): 

 A textbook which covers all static and 

 dynamic aspects of naval architecture, 

 both theoretical and applied. The book 

 concentrates on merchant ships, but in- 

 cludes discussion of submarine hydrody- 

 namics and design. A knowledge of cal- 

 culus, applied mechanics and theoretical 

 and applied fluid mechanics is a prereq- 

 uisite. 



Of the above publications reference (3) con- 

 cerns itself most directly with submersibles, 

 although other problems are addressed. In 

 addition to these there are a variety of re- 

 ports, both technical and non-technical, 

 which are referenced throughout this text. 



PROPULSION AND 

 MANEUVERING 



Ideally there are six degrees of freedom 

 (motion) desirable in the control of a sub- 

 mersible; these are shown in Figure 8.1 rela- 

 tive to an X, Y and Z axis and are classified 

 as translational and rotational motions. 



Translational motions occur when every 

 point of the submersible has simultaneously 

 the same speed and direction of motion. 

 These are Heave (vertically up/down), Surge 

 (forward/backward) and Sidle or Sway (lat- 

 erally left/right). 



Rotational motions occur around a center 

 point or axis. These are Yaw (rotation 

 around a vertical axis), Roll (rotation around 

 the principal longitudinal axis) and Pitch 

 (rotation around the principal transverse 

 axis). 



To varying degrees and through a variety 

 of means, both translational and rotational 

 motions, both singly and together, are ob- 

 tained by most contemporary submersibles. 



To acquire any or all of the six motions, a 

 submersible requires a component to propel 

 it and another to change its direction. In the 

 most basic arrangement, a screw-type pro- 

 peller provides forward/reverse translational 

 movement (surge), a rudder provides left/ 

 right movement (yaw) and a movable plane 

 or wings provide up/down (pitch) rotational 

 movement. We treat first the devices that 

 overcome the submersible's inertia, or make 

 it move. These are: Free propellers, ducted 

 propellers, Kort nozzle propellers, cycloidal 

 propellers and water jets. Next we examine 

 the devices that change its course or atti- 

 tude. These are: Rudder and planes, thrus- 

 ters and trim control. 



Fig 8 1 Translational and rotational motions. 



PROPULSION 



Free Propellers 



The simplest means of submersible propul- 

 sion is the screw propeller (Fig. 8.2). In con- 

 cept, the propeller can be thought of as 

 screwing itself through the water — analo- 

 gous to tapping a screw into a solid material 

 where the rate of advance distance for each 

 revolution is equal to the pitch of the thread. 

 In practice, however, a screw propeller in 

 water does not advance at a speed pn (pitch 

 X revolutions) per unit time. Instead, it trav- 

 els at some lesser speed which is a function 

 of the propeller slippage with each revolu- 

 tion. Thus, if a propeller having a pitch of 10 

 feet turns at 200 rpm, it would advance 2,000 

 feet in 1 minute in a solid; it does not do so in 

 water because of slip, the difference between 



371 



