What must a vessel nearing a bend sound to alert others?

A vessel nearing a bend must sound one prolonged blast to alert other vessels in the vicinity. This action communicates the vessel's presence, as visibility may be restricted in bends and turns where other vessels might not be able to see or anticipate its approach. The prolonged blast is a standard signal indicating that the vessel is navigating in a situation where it may not be visible to others, thus promoting safety by ensuring that nearby vessels are aware of its position.

In the context of maritime navigation rules, the use of sound signals is crucial for maintaining safe distances between vessels, particularly in areas where visibility is compromised. Therefore, sounding one prolonged blast serves as an essential communication tool in ensuring that other vessels are informed of the navigational situation.