USCG Exam PracticeSingle-screw maneuvering and prop walk
When a vessel is running ahead with the rudder put over, which additional force significantly increases the turning moment on the stern compared to rudder force alone?
- A. The suction screw current, which draws water toward the rudder face
- B. Propeller side force, which is greatest at ahead speeds
- C. The frictional wake, which concentrates flow on the low-pressure face of the rudder
- ✓ Approximately half the propeller's thrust directed to the side of the rudder deflectionCorrect
Why D is correct
USCG Boat Crew Seamanship Manual §10-B states that running ahead, putting the rudder over directs about half the propeller's thrust to that side, which is a major additional force on the stern beyond the hydrodynamic rudder force alone. The discharge current also increases flow past the rudder, compounding the effect.