b. Whirling. A shaft sags between two bearings. As it rotates, the stress pattern al- 

 ternates. If it rotates fast enough, it is in danger of whirling, a situation which may be com- 

 pared with the action of a skip-rope and one in which the fiber in tension remains in tension. 

 This condition is likely to be destructive and obviously would transfer large unbalanced 

 forces to the hull, through the bearings. This phenomenum was considered as possibly con- 

 tributing to the relatively high incidence of shaft failures noted on commercial ships at the 

 close of World War II. 



DTMB has studied this problem and in the past has issued several valuable papers 

 in this area, among which are TMB Report 827, "A Theoretical Approach to the Problem of 

 Critical Whirling Speeds of Shaft-Disk Systems," and Report 890, "A Design Approach to 

 the Problem of Critical Whirling Speeds of Shaft-Disk Systems." Both were authored by 

 Dr. N. H. Jasper. 



Although this phenomenum has not been established as a cause of the shaft failures, 

 the understanding of the phenomenum and its importance in the development of design cri- 

 teria for shafting systems should be pursued by DTMB in the future. 



3. Lateral 



0. Bending. Bending has been established as the major alternating load on propeller 

 shafts and is believed to be a major influence on the shaft failure problem. The phenomenum 

 has been adequately explained in the literature, the most recent publication being prepared 

 by DTMB in Report 1596 by Price, et. al., on "Bending and Torsional Stresses in Propeller 

 Shaft of USS OBSERVATION ISLAND (EAG 154) in Smooth and Rough Sea." Previous stud- 

 ies by DTMB included those of USS MISSION SAN LOUIS OBISPO, USS NORFOLK (DL 1), 

 and limited studies on several submarines of the SKIPJACK class. TMB Report 947, by 

 McGoldrick, presents "A Theorem on Bending Stresses in Rotating Shafts." 



The TMB program in this area includes additional proposed full-scale studies aimed 

 at the development of improved shaft design procedures. It should be realized, however, 

 that all efforts to reduce the alternating bending loads on the propeller shaft, introduced by 

 the eccentric thrust component, will in the final analysis, also serve to reduce the vibration 

 of the hull by the reduction of the alternating forces entering through the shaft bearings. 



b. Unbalance. Unbalance has long been recognized as the fundamental source of 

 vibration in rotating machinery. DTMB has been engaged in many studies on the influence 

 of unbalance forces in propulsion systems as a source of serious hull vibration. As ex- 

 plained in TMB Reports C-36 and C-414, unbalance, mass or hydrodynamic, was largely 

 responsible for serious hull vibration in a destroyer and an aircraft carrier. Although the 

 application of balancing tolerances of MIL-STD-167, "Mechanical Vibrations of Shipboard 

 Equipment," has served to reduce the vibratory forces from this source, nevertheless, a 



