Explanation: Ch-16 is the internationally recognized VHF distress, safety, and calling frequency. It is designated for initial voice contact and subsequent follow-on communications, especially for survival craft, after an alert has been raised. Vessels in distress use Ch-16 for voice communication with rescue services and other vessels, making it mandatory for portable survival craft equipment. Ch-6 is primarily an inter-ship safety and working channel for non-commercial traffic. Ch-13 is used for bridge-to-bridge navigation communication between vessels. Ch-70 is the Digital Selective Calling (DSC) channel, used for automated distress *alerting*. While crucial for initiating a distress call, Ch-70 is a digital channel for signaling, not a voice channel for follow-on communications. The voice follow-on occurs on Ch-16.