VHF radio is the primary short-range communications tool for mariners. Channel 16 is the international distress, safety, and calling channel that all vessels must monitor when underway. Knowing how to use VHF correctly — especially in a distress situation when time is critical — is a basic competency tested on every USCG license exam.
The three urgency levels
- MAYDAY — grave and imminent danger, lives at risk. Call on Channel 16: "Mayday Mayday Mayday, this is [vessel name], [position], [nature of distress], [number of persons on board], [other relevant information], over."
- PAN PAN — urgent situation but not immediately life-threatening. Used for medical situations, disabled vessels, or person overboard when the person has been recovered.
- SÉCURITÉ — safety message concerning navigational hazards, weather broadcasts, or obstructions.
DSC — Digital Selective Calling
Modern VHF radios include a dedicated DSC controller. A single press of the Distress button transmits a formatted digital signal on Channel 70 that includes your MMSI (vessel identity) and, if a GPS is connected, your exact position. This digital alert reaches all DSC-equipped vessels within range and the coast guard simultaneously — even if you cannot speak on the radio.
Registering your MMSI with BoatUS or Sea Tow (for recreational vessels) or the FCC (commercial) ensures the DSC alert can be matched to your vessel and contact information.