USCG Exam PracticeTwin-screw vessel handling
On a twin-screw vessel, what is the primary effect of running one engine ahead and the other astern with the helm amidships and no way on?
- A. The discharge screw current from each engine cancels all propeller side force.
- B. The vessel backs in a straight line due to balanced side forces.
- C. The vessel moves ahead with a strong turning tendency.
- ✓ The vessel rotates about its pivot point with little or no advance and transfer.Correct
Why D is correct
USCG Boat Crew Seamanship Manual §10-D states that with the helm amidships and no way on, clutching one engine ahead and the other astern turns the boat with little or no advance and transfer. This is the twin-screw twist maneuver, performed at clutch speed in calm water.