Which of the following signifies that a vessel is operating astern propulsion?

The indication that a vessel is operating with astern propulsion is through the sound of one long blast. In the context of maritime navigation, sound signals are crucial for communication between vessels, especially in congested waters or when visibility is restricted.

A long blast serves to inform other vessels that the ship is primarily moving backwards. This is vital for safety, as it alerts other navigators to the fact that the vessel may not be maneuvering in the usual forward direction and could be moving in reverse, which affects the intended course of action for both the vessel in motion and those around it. Knowing how to interpret these signals is essential for the safe operation of vessels in shared waterways.

The other sound signals you referenced serve different purposes. For example, two short blasts typically indicate that the vessel is planning to overtake another on its starboard side. Understanding these distinctions helps ensure safe navigation and prevents collisions at sea.