On twin-screw boats, where are the propellers typically located relative to the center line?

• A. Outboard of the center line
• B. Inboard of the center line
• C. Directly on the center line
• D. Behind the stern

Answer: (A)

On twin-screw boats the propulsion is designed so the two propellers sit to the sides of the ship’s centerline, toward the outboard hull. This outboard placement leaves room for a rudder to sit between the two propellers, giving effective steering and cleaner water flow to the rudder. It also reduces interference between the propellers’ wakes.

Putting the propellers inboard of the centerline would crowd the rudder area and worsen flow interaction, placing them directly on the centerline would clash with hull structure and steering components, and placing them behind the stern misstates their typical transverse (side-to-side) location relative to the centerline.