USCG Exam PracticeSingle-screw maneuvering and prop walk
A coxswain is backing a single-screw vessel and finds that rudder alone cannot hold the stern against the swing produced by propeller side force. After applying a corrective burst ahead with the rudder shifted, the coxswain must be careful to use the MINIMUM power necessary. What is the specific reason given for this caution?
- ✓ Too much ahead power kills sternway and sets up a discharge current that worsens the swing rather than correcting itCorrect
- B. High RPM during the ahead burst causes cavitation, aerating the water and reducing rudder effectiveness on the next astern application
- C. Excessive ahead power will shift the pivot point forward, reducing the effectiveness of the rudder during the subsequent astern phase
- D. Excessive ahead power increases suction screw current on the rudder, pulling the stern back toward the undesired side
Why A is correct
The manual explicitly cautions to use no more power than needed during the corrective ahead burst so that sternway is not killed and a discharge current is not set up that worsens the swing. Killing sternway eliminates the rudder effectiveness that had been building, and excessive discharge current can push the stern further in the wrong direction.