loss of speed and the greatest amplitude of pitching occurs as the wave lengths approach 

 the ship's length, [8], [9], [10]. 



On the basis of our present knowledge there is little we can do to greatly im- 

 prove the rough water performance of a conventionally designed ship. The evidence, 

 though meager, seems to indicate that minor changes in hull form, based on optimum 

 performance in smooth water, will not materially improve the rough water performance. 

 Obviously we must consider major changes in concept in order to attain, for example, 

 the same smooth performance for a surface ship in rough water as for a submerged 

 submarine. Much thought is being given to this problem, as evidenced by recent papers 

 on ship speeds and motions in regular and irregular seas [11], [12]. It is possible that 

 we may be at the threshold of some practical progress in this area [9], [13], 

 [14]. Successful control of rolling, to a reasonable degree, may be accomplished by 

 means of controlled fins [15], [16], [17]. Pitch damping is also under study and some suc- 

 cess seems indicated by the use of hydrofoils at the bow. These and major changes in 

 hull form above and below the waterline may produce a surface ship with considerably 

 improved performance characteristics in rough weather. 



The maneuvering of ships has always received much practical attention. For 

 many years what little we knew came from full scale tactical trials which were quite 

 common with naval vessels. From the designer's standpoint little theoretical advance 

 was made in the way of making it possible to calculate the turning and steering proper- 

 ties of a ship. At the present time it is still necessary to rely upon an empirical approach 

 to the calculation of tactical diameter and directional stability [18], which is an im- 

 portant element of course keeping. Model testing techniques have been developed to a 

 point where we can determine, with a high degree of confidence, the full scale per- 

 formance of a ship or submarine. However, it should be noted that here again, as in 

 wave making resistance we depend on the model test results rather than on a theoretical 

 solution of the turning problem. 



It is still practically impossible to determine, in the absence of specific model 

 tests, the force and moment characteristics of a ship [19]. The problem is complicated 

 by the fact that ships operate at the interface of two different fluid media and also by 

 the complex geometry of ship forms. Complete theoretical treatment is therefore 

 rendered very difficult. 



Great advances in the field of electronics have also affected our outlook and 

 trends in design. Electronics has made possible completely new evolution in missile 

 design, provided long range electronic eyes and ears which have affected the topside 

 as well as the under water parts of ship designs. The influence of radar is readily ap- 

 parent by comparing the topside structure of any modern naval surface ship with one 

 of 20 years ago. Sonar likewise is revolutionizing the design of naval vessels. The 

 capabilities of electronics have influenced the need for control of the motions of surface 

 ships and below the sea surface they have brought about the demand for reduced noise, 

 from any source, which may be transmitted through the water. While much noise is 

 associated with machinery and other components in the ship it is the hydrodynamic 

 noise that is one of our main concerns. This noise is caused principally by flow condi- 

 tions which produce cavitation, separation, and vortices. This is one hydrodynamic 

 barrier which is particularly important to the submarine. 



The exact mechanism associated with the generation of noise by flow over the 

 hull of a ship is not too well understood. Flow into the propeller, and propeller loca- 

 tion relative to the hull and other structures, are known to be important elements in 

 the noise problem. The problem is so complex that thorough theoretical research is 

 needed to guide our progress in noise reduction. 



The determination of the physical quantities which influence cavitation inception 

 is another one of our important needs [20], [21], [22]. The development of hydrofoil 

 shapes in which cavitation is delayed or avoided entirely has shown much progress due 

 to the work done by the aeronautical laboratories and by our model towing basins. 

 Cavitation is an important area for continued study particularly in connection with 



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