reasonable portion of our everyday difficulties may be attributed to unbalance. The plans of 

 DTMB for the future includes further study into the understanding and control of this problem 

 and in the development of improved specifications and standards. 



This review emphasizes the importance of machinery vibration to the response of a 

 ship hull. These same problems will also precipitate undesirable vibration of local struc- 

 tures under favorable circumstances. It is still an important consideration, however, that 

 to effectuate low vibration levels in ship structures, the best approach is to understand the 

 cause of and establish satisfactory methods for the elimination or reduction of the exciting 

 forces. 



B. INFLUENCE OF SHIP SUBSTRUCTURES 



The principal structures falling in the category of ship substructures are: deckhouses, 

 superstructures, masts, gun turrets, and missile launchers. 



DTMB plans to investigate ship substructures to establish vibration levels and deter- 

 mine the effects of these structures on hull vibration and hull-girder strength. This investi- 

 gation will include the effects of substructure configuration, method of attachment, and ma- 

 terials used for construction of these structures. 



1. Configuration 



a. Length of substructure relative to hull length (shear stiffness effect). 



b. Location of structure in respect to nodal points of hull vibration (strain limits and 

 mode effects). 



c. Height and width of structure. 



d. Shape of structure; i.e., superstructure decks may or may not be of uniform length. 



e. Effect of expansion joints. 



2. Method of Attachment 



a. Structures rigidly attached to ship hull girder. 



b. Flexibly mounted structures. 



3. Materials 



a. Steel. 



b. Alloy. 



c. Plastic. 



