Which statement best describes the arrangement of screws on twin-screw boats to maximize maneuverability?

Which statement best describes the arrangement of screws on twin-screw boats to maximize maneuverability?

• A. The tops of the blades turn outward; the starboard screw is right-handed and the port screw is left-handed; both propellers are outboard of the center line
• B. The tops of the blades turn inward; the starboard screw is left-handed and the port screw is right-handed; both propellers are inboard
• C. The blades turn outward; both screws are left-handed and inboard of the center line
• D. The blades turn inward; starboard is left-handed and port is right-handed; both screws are inboard

Answer: (A)

Maximizing maneuverability on a twin-screw boat comes from creating the largest yawing moment and lateral control at slow speeds. Placing the propellers outboard (farther from the centerline) increases the lever arm of their thrust, so the same amount of thrust produces a stronger turning effect. Giving the two screws opposite handedness—starboard being right-handed (clockwise when viewed from the stern) and port being left-handed (counterclockwise)—ensures their thrusts don’t cancel but instead drive the stern toward one side, enabling quicker, more precise turning. The blade geometry with the tops turning outward supports a thrust direction that favors this lateral, yaw-producing effect rather than pulling the hull straight ahead. Together, these choices produce the most responsive maneuvering, especially at low speeds or in tight quarters.

Maximizing maneuverability on a twin-screw boat comes from creating the largest yawing moment and lateral control at slow speeds. Placing the propellers outboard (farther from the centerline) increases the lever arm of their thrust, so the same amount of thrust produces a stronger turning effect. Giving the two screws opposite handedness—starboard being right-handed (clockwise when viewed from the stern) and port being left-handed (counterclockwise)—ensures their thrusts don’t cancel but instead drive the stern toward one side, enabling quicker, more precise turning. The blade geometry with the tops turning outward supports a thrust direction that favors this lateral, yaw-producing effect rather than pulling the hull straight ahead. Together, these choices produce the most responsive maneuvering, especially at low speeds or in tight quarters.