VI 

 HYDRODYNAMIC BARRIERS IN SHIP DESIGN 



J. C. Niedermair 

 U. S. Navy Bureau of Ships 



A discussion of some of the related unsolved problems and the continued 

 necessity for the application of empirical methods to the design of ships. 



The naval architect is surrounded with barriers of varying degree of density 

 in practically every phase of his work in ship design that is related to hydrodynamics. 

 Barriers exist in the theory and mathematics, the experimental work in the laboratories, 

 the full-scale performance of the ship, the weather and the sea its affects, and in a large 

 measure in custom and tradition. Certain hydrodynamic barriers that exist for the 

 surface ship vanish in the case of the submarine. 



Aside from the barriers associated with hydrodynamics there is an economic 

 barrier. The very physical size of a ship and its cost and time required for construction, 

 constitute a most formidable barrier to progress. The aircraft designer is seldom ex- 

 pected to produce a successful plane in his first try. Several experimental planes are 

 built and tested before a prototype is reached. Not so with a ship, every piece of equip- 

 ment and machinery must be tried and true so that the very first prototype will be 

 successful or very nearly so in meeting all the essential requirements. 



The demands for the attainment of more advanced properties in our ship designs 

 are becoming more and more urgent due to the changing technology of the times in 

 which we are living. The fact that the art of shipbuilding is among the oldest known to 

 man has in a large measure handicapped the scientific side of our work. In a period 

 when newer industries were making rapid progress through a more scientific approach 

 the need for theoretical research was not considered an essential part of the naval archi- 

 tect's work because great success had been attained by evolution and watchful attention 

 to the performance of full-scale ships. Fortunately, or possibly unfortunately, our 

 predecessors were so very successful in meeting their requirements on the basis of good 

 judgment that the need for more extensive theoretical work was not readily apparent. 

 Ship hydrodynamics was, in a sense, a plaything for the theoretical minded but of little 

 import to the practicing naval architect. In the meantime the competitive aircraft in- 

 dustry has come along in giant steps largely on a basis of theoretical and applied re- 

 search. Because of this, and the many advances in the fields of physics, we too feel com- 

 pelled to encourage the scientific approach. 



In this brief discussion reference will be made to a few of the important barriers 

 we have been dealing with in the past and to some of the more important ones which 

 may limit our progress now and in the future. The specific areas of importance are 

 speed, frictional and wave-making resistance, rough water performance, maneuvering, 

 flow noise, and cavitation. 



To obtain speed at the least cost has been one of our ever present problems and 

 it is in this area that our experimental towing tanks have made their greatest contribu- 

 tion to our work in hull form and propeller design. The price of ship speed is often 

 not fully realized, especially when we note the tremendous progress that has been made 

 in the speed of airplanes. Because of this progress in aviation it is often wondered why 

 ships seem to be standing still in this matter of speed increase. The answer is quite 



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