224 OCEANOGRAPHY IN THE UNITED STATES 



To find out what ships are subjected to under realistic operating conditions we 

 have developed simple apparatus for automatic collection of stress and motion 

 data on ships at sea. We have found, as a result of these tests, that stresses 

 arising from temperature changes in the structure, and stresses associated with 

 slamming of a sliip in a seaway can be as important, or more so, than stresses 

 associated with l)uoyancy and weight forces acting on the ship, which are the 

 only forces entering into the traditional structural hull design procedure. 



As an illustration of the value of full scale sea tests I wall mention the meas- 

 urements made by us on the carrier Essex during a storm passage around Cape 

 Horn in 1957. The main puri>ose of these tests was to explain the extensive 

 structural damage suffered by Ticomleroya during a similar passage. The 

 tests showed that severe vibratory whipping of the entire ship could be asso- 

 ciated with deep immersion of the bow in an oncoming wave. The resultant 

 vibratory stresses were several times as large as the ordinary slowly varying 

 wave-induced stresses. We thus have here a mechanism of loading and stress- 

 ing which undoubtedly caused the damage of Ticondcroya, and which should 

 be taken into account in ship design. It is very likely that this phenomenon 

 (slamming) is a prime factor limiting the speed capabilities of ships in rough 

 seas. 



Ship type developments are underway for very high speed ships ; here we will 

 be faced with problems of devising structures to withstand the severe water 

 impact loads expected in rough seas as well as hydrostructural problems not 

 experienced in the past. 



Technological improvements, especially the advent of nuclear power, will per- 

 mit high sustained ship speeds, provided that the structural strength of the ship 

 is adequate to withstand the loads imposed by the sea. I am sorry to say that 

 lack of adequate structural strength does limit the oiJerational speed capabilities 

 of a surface vessel in rough seas. Submarines do not have this limitation. 

 Consequently, the ability of a surface vessel to maintain sustained high speed 

 in order to keep up with the enemy submarines is of prime importance in 

 antisubmarine warfare. Other reasons for requiring sustained sea speed can 

 easily be developed. 



To make reasonably valid predictions of strength requirements requires a 

 fair estimate of the wave conditions expected by ships in service and the rela- 

 tive exposure of ships to these conditions. With the wave conditions specified 

 it may be possible to develop model test procedures and analytical means for 

 estimating the structural strength requirements together with the vibratory 

 conditions to be expected on shipboard. 



The Significance of Oceanography to the Underwater Acoustics Program 

 AT THE David Taylor Model Basin 



(By Mark Harrison, Ph. D.) 



In order to properly depict the significance and relevance of oceanographic 

 studies to the underwater acoustics program at the David Taylor Model Basin, 

 it is desirable to give a brief sketch of what we do. 



The underwater acoustics program at the David Taylor Model Basin is prin- 

 cipally concerned with noise generated by submarines and surface ships. We 

 are interested in i^wo aspects of this noise. One aspect is the noi.se which is 

 propagated through the ocean to large distances and which can be detected 

 by enemy shii)s. The other aspect of this noise is that it interferes with the 

 operation of the ship's own sonar and thereby inhibits the ship's offensive 

 cai)abilities. 



In the prosecution of this program we encounter many problems that have 

 oceanographic aspects. By and large, however, we are a consumer of the infor- 

 mation that comes from our oceanographic institutions rather than a creator 

 of such information. For example, in measuring the noise propagated away 

 from our sbii>s, it is necessary to use data on the thermal structure and the 

 bottom topography of the ocean. To a large extent such data is fairly well 

 known though there still exists many large gaps in existing knowledge. Spe- 

 cifically, we need much better data on the small inhomogenities that scatter 

 sound. These small inhomogenities are local temperature fluctnuations, marine 

 life, and local currents. 



