Two Way Radios - Marine:
Marine VHF radio operates in the VHF frequency range, between 156 to 174 Mhz. A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels.
Channel 16 is the international calling and distress channel.
Channel 9 can also be used in some places as a secondary call and distress channel.
Transmission power ranges between 1 and 25 watts, giving a maximum range of up to about 60 nautical miles (111 km).
Marine VHF mostly uses "simplex" transmission, where communication can only take place in one direction at a time.