To determine ship characteristics which guarantee a good behavior in a seaway, 

 we need a complete survey of all ship motions. This exceeds by far the scope of the 

 present paper. Our aim is rather to indicate simple methods which, duly extended, 

 will enable us to meet requirements of present and future practice. We shall restrict 

 ourselves to some remarks on roll, heave and pitch. Future extension in knowledge will 

 modify the procedure and results here indicated. 



2. Transverse Stability and Roll 



Froude's work on roll has been widely used in design. The importance of the 

 tuning factor A and of the factor of magnification ^ with its dependency upon 

 damping has been clearly understood. However, because of limitations of the linear 

 theory more advanced considerations must be introduced to cope with the safety prob- 

 lem. A most urgent task is to evaluate the influence of the shape of Reed's diagram on 

 the behavior of a vessel. So far this question has been discussed on a hydrostatic basis 

 only. 



Even such an elementary approach shows that there may be an appreciable 

 loss of "stability" (restoring moment in roll) in waves under certain conditions [62]. 

 Thus minimum requirements for the metacentric height and the curve of righting arms 

 (Reed's diagram) derived from calm water conditions and from some statistical infor- 

 mation must be raised, especially in the case of smaller cargo ships. 



A standardization of the minimum values of stability parameters will rest on 

 future research dealing with the actual pressure distribution around a rolling ship and 

 the non-linear character of roll prevailing at large angles. 



Valuable information is now being collected on damping as well as exciting 

 forces. There is a tendency at present to underestimate the bearing of such scientific 

 activities on the design of ship hulls because of the application of antirolling devices. 

 It should not be overlooked, however, that an adequate understanding of the hydro- 

 dynamic phenomena involved may be a prerequisite for a successful development of 

 stabilization. Reference is made to various effects mentioned before, especially the 

 sway-roll effect; earlier lack of knowledge in this field has caused serious setbacks. 



The present state of roll stabilization can be described by quotations from a 

 paper by Chadwick [17]: 



1. "the technical feasibility of stabilization is an established fact" 



2. "the control system no longer should prove a limitation on system perform- 

 ance." Ideas are being developed at present to recover some of the seaway energy for 

 stabilizing purposes. 



3. "At least some feedback control should always be used. Arguments for feed- 

 ahead control, predictors, etc. have largely been negated by advances in control 

 technology." This statement, if corroborated, would dispose of the attempts of a school 

 of thought which preached the superiority of feedahead control. 



4. "For stabilization at speeds of 15 knots and above activated fins provide the 

 most efficient system. Tanks and gyros are still worthy of consideration in low speed 

 application." This assertion again practically means the victory of fins since there is not 

 too much interest in low speed application. 



We refer further to two principles of stabilization which we consider as impor- 

 tant notwithstanding some doubts expressed [Ref. 17, discussion]: 



1 . with respect to the true horizon, 



2. with respect to the effective wave surface; 



the first one being the natural solution for men of war, the second presenting advan- 

 tages for passenger vessels. Recently these ideas have been generalized [63]. 



3. Heave and Pitch 



After a brighter outlook has been gained in the case of roll the primary interest 

 is now concentrated on obtaining favorable "symmetric" motions (pitch and heave). 



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