OCEANOGRAPHY IN THE UNITED STATES 223 



sirable effects which have been noted, specifically a serious vibration problem. 

 This i)heuomenon can be studied very well by means of this model. 



We also do a large amount of full .scale work, in order to determine the actual 

 responses of a vessel to the environment in which it is forced to live. For in- 

 stance, we are carrying out jointly with the Maritime Administration an exten- 

 sive investigation of the motions of commercially operated vessels and the seas 

 which they encounter. You see here models of two vessels which were used 

 in this program. The first of these is a Liberty Ship, of which there are hun- 

 dreds in existence, many of them tied up in mothballs. This vessel has a poor 

 reputation for its behavior in a seaway. The Maritime Administration would 

 like to make it more attractive to the operators by improving its performance. 

 This second model, which is almost identical, is also a Liberty Ship. However 

 the bow has been rebuilt, and lengthened about 25 feet. As you can see, the 

 change is not great. 



Two winters ago, we carried out trials on these vessels while they were being 

 operated by the United States Lines in the North Atlantic service. We partici- 

 pated in a number of round trips on both vessels, and accumulated an enormous 

 amount of very valuable data. The analysis of this data has not yet been com- 

 pleted, but we know that the slight change in ship form improved the behavior 

 of the vessel greatly. The average speed of the modified vessel is 1 to 2 knots 

 better than that of the unmodified vessel, under all conditions. Under adverse 

 storm conditions, the difference Ls even more spectacular. Under conditions in 

 which the original vessel would barely be able to maintain headway, the length- 

 ened vessel would be able to maintain steady progress. We are continuing our 

 close relations with the Maritime Administration, and in the near future we 

 intend to carry out further trials on selected commercial vessels. These studies 

 will provide a basis for better design, thus making it possible to move cargoes 

 faster and cheaper. 



Finally, I would like to mention a development project which in a sense is 

 more or les^s routine, but which deals with a subject vei-y close to our hearts, 

 and which I think will be of very great interest to this committee. We were 

 asked to investigate the behavior in waves of an oceanographic research vessel. 

 We prepared a technical report in the form of a motion picture, and I would 

 like to show you a portion of this film. (The film includes a statement of the 

 oi>erational requirements for a vessel designed for oceanographic purposes, and 

 a few runs of the model in waves. ) 



On the Strength of Ships at Sea 

 (By N. H. Jasper) 



The ship structure, machinery, and shipboard equipment must be designed to 

 perform their functions under all sea conditions encountered, particularly in 

 Aery rough seas. 



As illustrations of what can happen if the structural strength is inadequate 

 we could recall that (a) the Pittsburgh lost its bow in rough seas, (ft) Liberty 

 ships have fractured during rough sea conditions, (c) a number of aircraft 

 carriers of the Essex class have suffered major damage to the main hull girder, 

 the last example being the buckling of the main deck of Ticonderoga during a 

 passage around Cape Horn, {d) numerous instances of local bow damage suf- 

 fered in rough seas occur. 



The David Taylor Model Basin has carried out a continuous program to 

 evaluate the relative significance of the various sources of stresses, and the 

 mechanism by which they may be predicted. As the stresses induced by wave 

 action are, very roughly, most severe in heavier seas, particular attention has 

 been devoted to tests of ships at sea. 



The ship, though built of steel, is quite flexible and for purposes of visualizing 

 the deformation under load may be thought of as made of rubber, fairly stiff 

 rubber to be sure. When forces are applied to the ship it tends to vibrate and 

 these vibrations set up stresses in the ship structure. When the stresses exceed 

 the strength of a structure it may collapse or deform excessively and thus fail to 

 serve its purpose. Even if stiiictural failure does not occur the environmental 

 ship vibrations may be severe enough to cause maloperation or failure of shii> 

 board equipment, such as fire control or navigational equipment. 



