With the starboard screw astern and the port screw stopped, the stern will move to ______.

With the starboard screw astern and the port screw stopped, the stern will move to ______.

• A. Port
• B. Starboard
• C. Forward
• D. Aft

Answer: (A)

When a vessel has two screws, steering is influenced by asymmetrical thrust. If the starboard propeller is in astern (reversing) and the port propeller is stopped, the only thrust acting on the hull is a reverse thrust on the starboard side. That thrust is applied off the centerline, creating a yawing moment. The reaction of that off-center thrust tends to swing the stern toward the opposite side of the thrust, which is port. Since there’s no thrust from the port side to balance it, the stern moves to port (left) while the bow moves toward starboard. This is how the boat yaws when one engine is reversed or stationary.

When a vessel has two screws, steering is influenced by asymmetrical thrust. If the starboard propeller is in astern (reversing) and the port propeller is stopped, the only thrust acting on the hull is a reverse thrust on the starboard side. That thrust is applied off the centerline, creating a yawing moment. The reaction of that off-center thrust tends to swing the stern toward the opposite side of the thrust, which is port. Since there’s no thrust from the port side to balance it, the stern moves to port (left) while the bow moves toward starboard. This is how the boat yaws when one engine is reversed or stationary.