What do the port and STBD hand cranks control in the AFT steering?

The port and starboard hand cranks are specifically designed to control the position of the rudder in the aft steering system of a vessel. By adjusting the cranks, operators can change the angle of the rudder, which directly influences the vessel's directional movement. This is crucial for maneuverability, especially in situations where precise steering is required, such as docking or navigating through narrow channels.

In contrast, options related to the speed of the main engines, heating systems, and deck lights do not pertain to the steering mechanics of a vessel. The speed of main engines is typically controlled through throttle systems, heating systems are managed through specific climate controls onboard, and deck lights are controlled through electrical switches or circuits. Therefore, the only function relevant to the hand cranks in the context of navigation and steering is the adjustment of the rudder's position.