What does the signal "_ _ . . OR . ." indicate to other vessels in terms of passing?

The signal represented by "_ _ . . OR . ." is a specific sound signal used by vessels to communicate their intentions to others. In maritime communication, when a vessel uses this sound signal, it indicates its intention to pass another vessel on the port side. This is part of the sound signaling conventions outlined in the COLREGs, which are established to ensure safe navigation and communication between vessels at sea.

Understanding the importance of this signal is crucial for maintaining safety and avoiding collisions. It clearly conveys to other vessels what the signaling vessel plans to do, allowing them to take any necessary actions to facilitate safe passing. This communication is essential, especially in situations where visibility might be limited or where vessels are in close quarters.

The other options, such as indicating a passing on the starboard side or approaching a harbor, do not align with this particular sound signal and might lead to confusion or misinterpretation between vessels. Therefore, recognizing and correctly interpreting this signal, along with others, is vital for safe maritime operations.