USCG Exam PracticeSingle-screw maneuvering and prop walk
When a vessel is making sternway, rudder effectiveness is reduced primarily because the rudder lies in which flow?
- ✓ The suction screw current, which is neither as strong nor as concentrated as the discharge currentCorrect
- B. Aerated water produced by propeller cavitation ahead of the blades
- C. The discharge screw current, which is strong and concentrated
- D. The frictional wake, which reverses direction when the vessel backs
Why A is correct
USCG Boat Crew Seamanship Manual §10-B explains that when running astern the rudder lies in the screw suction current, which is neither as strong nor as concentrated as the discharge current, so the rudder cannot direct propeller thrust and steering depends mainly on water flowing past the rudder due to sternway.