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10.9 - Overlapping Propellers - Coggle Diagram
10.9 - Overlapping Propellers
Twin Screws
Overlapping propeller fields
Reduction in power
5 to 8%
Compared to single screw
20 to 25%
Compared to regular twin screw
Minor importance
Longitudinal distance BTW propellers
Direction of rotation of the aft propeller
Pitch of the aft propeller
Centre line distance
Optimum 0,7D
Induced Vibrations
Higher by 50%
compared to 4 bladed propeller
Shaft bending
not really meaningful
Different velocities
Alternating vertical and torsional
excitations of hull
caused by pressure fluctuations
Tip vortex interaction
Unfavourable
Negligible risk of
erosion
as bubble cavitation
not observed