VHF Marine Band
F5. The Reference Layer: Glossary, Units, Signals and Information SourcesDefinition
156 to 174 MHz radio band used for maritime communications.
The VHF marine band runs 156 to 174 MHz, divided into simplex and duplex channels by ITU Appendix 18. Channel 16 (156.8 MHz) is the international distress, safety, and calling channel, monitored continuously and reserved for DSC alerting and voice MAYDAY, PAN-PAN, and SECURITE traffic. Channel 13 (156.65 MHz) is bridge-to-bridge navigation safety; channel 70 (156.525 MHz) is DSC digital calling only, never voice. Typical VHF range at sea is line-of-sight, roughly 20 to 40 nautical miles ship to ship.
Source: ITU Radio Regulations Appendix 18