USCG Exam PracticeTwin-screw vessel handling
A single-screw vessel and a twin-screw vessel are each maneuvered to rotate in a confined space with minimal advance and transfer. Which statement BEST contrasts the technique each vessel uses to achieve this?
- A. The single-screw vessel uses asymmetric thrust between two engines; the twin-screw vessel uses alternating bursts ahead and astern with the rudder over.
- B. Both vessel types use the same technique: alternating bursts ahead and astern with the rudder amidships, because side force is the dominant turning force in both cases.
- ✓ The single-screw vessel uses alternating bursts ahead with rudder over and bursts astern, relying on side force; the twin-screw vessel uses opposed thrust — one engine ahead, one astern.Correct
- D. The single-screw vessel uses the discharge current directed by the rudder for all turning; the twin-screw vessel uses only the suction screw current from the astern engine.
Why C is correct
USCG Boat Crew Seamanship Manual §10-E describes the single-screw compound maneuver as alternating short bursts ahead with the rudder over against bursts astern, using side force to walk the boat around. USCG Boat Crew Seamanship Manual §10-D describes the twin-screw equivalent as clutching one engine ahead and the other astern to rotate about the pivot point. These are distinct techniques that achieve similar results.