USCG Exam PracticeTwin-screw vessel handling
The discharge screw current is described as stronger and more concentrated than the suction screw current. What is the practical consequence of this characteristic for vessel handling?
- ✓ A vessel handles quite differently going astern than going ahead.Correct
- B. A vessel accelerates more quickly going astern than going ahead.
- C. Rudder effectiveness is equal whether the vessel has headway or sternway.
- D. Propeller side force is eliminated when the vessel is backing.
Why A is correct
Because the discharge screw current is always the stronger and more concentrated of the two, the flow patterns around the hull and rudder differ significantly between ahead and astern operation, which is why a vessel handles quite differently going astern than going ahead. (USCG Boat Crew Seamanship Manual §10-A)