Design Method for Contra-Rotating Propellers for High-Speed Crafts: Revising the Original Lerbs Theory in a Modern Perspective

Table 4

	Case B-1	Case B-2	Case B-3
Front number of blades	4	5	4
Aft number of blades	4	5	4
Front EAR	0.84	0.93	0.84
Aft EAR	0.97	1.07	0.97
Strength margin	5	5	5
Cavitation margin fore	0.78	0.78	0.78
Cavitation margin Aft	0.7	0.7	0.7
Unloading curve	Y	Y	N
Propeller efficiency	0.648	0.646	0.650