Question 66 OSV01 - Master/Chief Mate - Offshore Supply Vessels

The Correct Answer is A. ### Explanation of Correct Option (A) Option A is correct because both the main rudder and the flanking rudders are used synergistically to maximize the push required to move the stern to port (and thus turn the vessel). * **Goal:** Move the stern of the tug to port (i.e., turn the bow to starboard) while going astern. * **Main Rudder (Hard to Port):** When a conventional propeller is turning astern (reverse thrust), the water flow hits the main rudder. To move the stern to port, the rudder must be positioned to deflect the reverse water flow (propeller wash) towards starboard. Deflecting the astern flow to starboard pushes the stern of the vessel to port. With most conventional systems, this requires the main rudder to be set **hard to port** when backing. * **Flanking Rudders (Hard to Port):** Flanking rudders are situated ahead of the propeller and are specifically designed to steer the vessel when going astern (reverse thrust). When the propeller is generating astern thrust, the water flows forward past the flanking rudders. To push the stern to port, the flanking rudders must be set to port. This directs the forward-moving propeller wash strongly to starboard, maximizing the lateral push on the hull, moving the stern **hard to port**. Combining both rudders set **hard to port** generates the maximum necessary force to move the stern quickly to port when maneuvering astern. ### Explanation of Incorrect Options **B) The rudder is amidships and the flanking rudders are hard to port** While the flanking rudders are correctly positioned to move the stern to port, the main rudder being amidships significantly reduces the steering effectiveness. The main rudder cannot contribute to deflecting the propeller wash, resulting in a much weaker and slower turn compared to using both systems simultaneously. **C) All of the rudders are hard to starboard** Setting the rudders hard to starboard when going astern would direct the propeller wash to port. This action would cause the stern to move strongly to **starboard**, which is the opposite of the desired goal (moving the stern to port). **D) The rudder is hard to port and the flanking rudders are hard to starboard** This option creates conflicting forces. The main rudder (hard to port) is attempting to move the stern to port, but the flanking rudders (hard to starboard) are attempting to move the stern to starboard. This results in counteracting forces, minimal stern movement, and poor control. Maximum confined turning requires all effective steering surfaces to work in unison.