Sec. 59.17 



PROPULSION-DEVICE PERFORMANCE 



351 



40 



30tl- 



lEO+j- 



20 40 60 80 100 



Blade- Position Anqle, deq 



Fig. 59. P Thrust Variation on a Victory 

 Ship Propeller, A = 11,606 Tons 



the presence of adjacent ship structure or append- 

 ages. 



The results of these calculations are published 

 by H. R. Neifert and J. H. Robinson in "Further 

 Results from the Society's Investigation of Tail- 

 shaft Failures" [SNAME, 1955, pp. 495-550], 

 where the authors give graphs showing various 

 force and moment variations with angular blade 

 position. Figs. 59.0 and 59.P, adapted from 

 Figs. 34 and 35, respectively, of the reference, 

 show the variation in total thrust for the pro- 

 peller; that is, the resultant of the thrust forces 

 on all four blades. They also show the thrust 

 eccentricity, corresponding to the offset from the 

 propeller-shaft axis of the center of pressure CP 

 of the total thrust load exerted axially forward on 

 the entire projected blade area of the propeller. 

 The third set of graphs indicates the angular 

 position of this CP when a given blade is in any 

 one angular position. Thus the horizontal scales 

 at the bottom of each diagram apply to all three 

 graphs on that diagram. For example, if in Fig. 

 59.0 a blade is at 20 deg, the total instantaneous 

 thrust of the whole propeller is just over 120,000 



lb. The thrust eccentricity, or the offset of the 

 CP from the shaft axis, is about 1.28 ft. The 

 angular position of this CP, read from the upper 

 right-hand vertical scale, is about 48 deg. In 

 fact, regardless of the blade positions, it remains 

 between 38 deg and 92 deg. 



Fig. 59.0 is calculated for a displacement of 

 8,268 tons, with a trim of 7.5 ft by the stern and 

 a draft at the AP of 20.5 ft, not quite sufficient 

 to cover the upper blade tips when the vessel 

 is at rest. Fig. 59. P is calculated for a displace- 

 ment of 11,606 tons with a trim of 3.83 ft by the 

 stern and a draft at the AP of 24.50 ft. This 

 places the propeller tips at the 12 o'clock position 

 well below the surface in the at-rest condition. 



Figs. 59. Q and 59.R, adapted from Figs. 36 

 and 37, respectively, of the Neifert and Robinson 

 reference, show the corresponding variation in 

 torque with angular position of the propeller, for 

 the two displacements and trims listed in the 

 preceding paragraph. They show also the magni- 

 tude of and variations in the upward vertical 

 force resultant and the starboard transverse force 

 resultant with angular position for the two dis- 

 placements and trims. 



8000 



L 460 



8000 



6000 



AO 60 60 



Blade- Position Ani^le, deq 



Fig. 59. Q Variation of Torque and Vertical 



AND Horizontal Forces for Part of a Propeller 



Revolution on a Victory Ship, U.S.N.S. 



Li. James E. Robinson, A = 8,268 Tons 



