2613. What type of propeller consists of a flat disc set flush with the under surface of the vessel's hull with a number of vertical, rudder-like blades projecting from it?

Cycloidal propellers feature vertical blades projecting from a flat disc flush with the hull, enabling thrust in any horizontal direction. This design, often known as the Voith-Schneider propeller, differs from helicoidal, tandem, and contra-rotating propellers, which utilize conventional screw propeller arrangements.