Sec. 69.15 



GENER/VL DESIGN OF PROPULSION DEVICES 



581 



It is usually easy to design or to alter local 

 structures or small parts of the ship to keep their 

 resonant frctiucncies out of the range of propdev 

 rpm or blade frequencies at speeds where the 

 exciting forces are high. However, to make 

 material changes in these characteristics of the 

 hull proper, or of large parts of it, is often well- 

 nigh impossible. 



Probable torsional and longitudinal resonant 

 fre(]uencies of the propulsion-device-shaft-gear- 

 turbine (or motor) system are likewise estimated, 

 to insure that they do not fall within the range of 

 shaft or blade frequencies at or near service 

 power or maximum desigued power [Sullivan, 

 E. K., and Scarborough, W. G., SNAME, New 

 Engl. Sect., Apr 1952]. 



