Module 4 - Channels & Frequencies
VHF Channel 16 vs Channel 70: voice calling and DSC
Start with the situation. Grave and imminent danger requiring immediate assistance is distress; concern for the safety of a person or vessel is urgency; navigational or meteorological warning traffic is safety; ordinary coordination is routine. The chosen label controls the procedure as well as the channel.
Channel 70 carries the digital selection or alert. Channel 16 carries the distress voice message and specified urgency, safety or initial-calling voice stages. A nominated, accepted or instructed working channel then carries the detailed non-distress traffic where the procedure calls for it.
The table is a decision aid for revision, not a substitute for the complete distress, urgency, safety or DSC module. In use, read the radio acknowledgement and current station instruction rather than forcing every case into one remembered route.
| Situation | First contact | Voice route | Critical guardrail |
|---|---|---|---|
| Distress | DSC distress alert on 70 when available | Mayday call and message on 16 | Do not delay justified distress traffic for routine channel etiquette |
| Urgency to all ships | DSC All Ships Urgency call | Announcement on 16, message on nominated working channel | Use the real urgency procedure, not a routine call with urgent wording |
| Safety information to HM Coastguard | Individual DSC safety call when supported | Working channel indicated in the acknowledgement | If unsupported, MCA guidance gives a voice call on 16 |
| Routine inter-ship, MMSI known | Individual DSC routine call | Accepted inter-ship channel | Do not speak on 70 |
| Routine inter-ship, MMSI unknown | Brief low-power voice call on 16 | Agreed inter-ship channel | If unanswered, the documented bridge-to-bridge fallback is 13 |
Optional quick check
Section 4 of 9
An Individual DSC safety call to HM Coastguard is acknowledged with a working channel. What should the operator do next?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Practice choosing the right VHF channel
The channels module links distress, DSC, inter-ship, port and working-channel choices to realistic call decisions.