Giddings and Wermter 



Table 3 

 Fin Particulars 



In 1962, Stefun and Schwartz [51] presented the results of a study conducted 

 to determine the effects of various bow fin configurations on hull vibrations. 

 These tests were conducted on an aircraft carrier model using 16 different fin 

 configurations as shown in Fig. 28. All tests were conducted at one wavelength 

 (\/h = 40, 30, and 24). The results of this study are presented in Fig. 29 as a 

 figure of merit. This figure is defined to mean that for any fin, n 



Pitch Reduction (Fin N)/Pitch Reduction (Fin 1) _ f m •+ 



Vibration Level (Fin N)/Vibration Level (Fin 1) ~ ^^^^^ ^^ ^^^i^^- 



While none of the fins completely eliminated transverse hull vibrations, 

 considerable improvement was indicated by several configurations. Aspect ra- 

 tio, tip fences or increased depth of submergence showed improvements. Holes, 

 dihedral angle and swept edges showed less improvement and while annular fins 

 indicated promise, the test results showed much more research would be re- 

 quired before their entire nature would be understood. 



In 1961, Ochi [52] conducted a very complete hydroelastic study on a ship 

 equipped with an anti-pitching fin. In addition to forwarding an explanation as to 

 the mechanism of the induced vibration the study also discussed the effect of the 

 fin location, size and configuration. 



While there is general agreement that the induced vibration is caused by a 

 cavity collapse (or cavity collapse plus fin slam in the case of shallow draft), 

 the study differs as to the cause of the mechanism inducing the vibration. The 

 premise forwarded here is that rather than the vibration being purely horizontal 

 in nature, it is initially a torsional vibration. If the natural frequencies of both 

 the torsional and horizontal modes correspond, the vibration is severe. 



782 



