Giddings and Wermter 



prediction of ship motions has been in the longitudinal plane, while in contrast, 

 the writers on motion stabilization have been more interested in the lateral mo- 

 tions. This may well be due to the almost linear and seemingly manageable na- 

 ture of pitch and heave motions which attracts theorists away from nonlinear 

 rolling and turning problems, while the highly commercial nature of roll and 

 course stabilization has attracted inventors and engineers. 



The paper will provide a brief survey of the state of the art in stabilizing 

 the motions of translation, course keeping, roll stabilization and pitch stabiliza- 

 tion. The latter of these is to be the subject of a more elaborate discussion. 



SURVEY OF THE ART 



Translatory Motion Stabilization 



The deliberate stabilization of translatory motions of conventional ships has 

 very little technology or theory to survey. While it could be said that mooring 

 problems are problems of stabilization and control of lateral translation, the 

 process of mooring is more an art in the classical sense than in the scientific 



sense. 



I 



Shipboard devices which affect lateral motion directly include bow thrusters, 

 vertical axis propellers and right angle drives. The application of these devices 

 to conventional ships has been for purposes other than "stabilization," as de- 

 fined in this paper. 



In the case of submarines, hydrofoils, and ground effect machines, the con- 

 trol of vertical translation has received a great deal of attention, but this subject 

 would warrant an extensive survey of itself, beyond the scope of the paper. 



It should be recognized that the physics of ships is such that pitch and 

 heave, yaw and sway, and roll and sway are so strongly coupled that control or 

 stabilization of the angular partner of each couple inevitably affects the other. 

 The effect on translatory motion is a by-product of the angular stabilization, 

 rather than a deliberately sought objective. 



Translatory accelerations on the order of one-tenth of gravity are not unu- 

 sual. In order to have significant direct effects on such motions, control forces 

 on the order of 5 to 10 percent of the ship weight would be needed. Generation 

 of such forces by direct means is impracticable. 



Yaw Stabilization 



Stabilization or control of yaw is the most ancient of stabilization problems. 

 It is actually not vital that a ship be stable in yaw, but it is vital that it be con- 

 trollable. Provision of adequate stability and controllability for ships is such 

 an obvious necessity, that years of tradition and experience provide useful de- 

 sign rules. References 1 and 2 provide useful information on the selection and 



748 



