USCG Exam PracticeTwin-screw vessel handling
Which statement BEST distinguishes the discharge screw current from the suction screw current?
- ✓ The discharge screw current is stronger and more concentrated, and this difference explains why a vessel handles differently going astern than going ahead.Correct
- B. The discharge screw current exists only when the propeller turns ahead; the suction screw current exists only when turning astern.
- C. The suction screw current is stronger and more concentrated than the discharge screw current.
- D. Both currents are equal in force but opposite in direction, so their effects on steering cancel out.
Why A is correct
USCG Boat Crew Seamanship Manual §10-A states that the discharge screw current is always the stronger and more concentrated of the two, and explicitly cites this as the reason a vessel handles quite differently going astern than going ahead. Both currents exist regardless of the direction of propeller rotation.