What channel must all compulsory, non-GMDSS vessels monitor at all times in the open sea?

In maritime communication, vessels are required to monitor specific channels to ensure safety and effective communication at sea. The correct answer is that all compulsory, non-GMDSS (Global Maritime Distress and Safety System) vessels must monitor Channel 16 at all times when in the open sea.

Channel 16 operates at a frequency of 156.8 MHz and is designated as the international distress, safety, and calling channel. It is crucial for two primary reasons: first, it is the primary frequency used for distress calls, allowing vessels in emergency situations to communicate their distress and request help. Second, Channel 16 is also used for establishing communication between vessels before switching to a working channel for further discussion.

Monitoring this channel ensures that vessels are able to receive important safety information and distress signals from other vessels, contributing to the overall safety of maritime navigation. It's a fundamental regulation that enhances situational awareness and promotes a responsive maritime environment.

The other channels mentioned are designated for different purposes and are not required to be monitored continuously by vessels in the same manner as Channel 16.