NASA SX 35 DSC - Manual (Page 55)

SX 35 DSC 53
Channel Assignments
The Channel Assignment tables on the following pages list the channel num-
ber, frequency and usage for Marine VHF communication as published by
the Radiocommunications Agency.
Depending upon your selection, certain channels may be either simplex
(single frequency) or duplex (two frequency) as indicated in the tables.
On simplex channels, your transceiver transmits and receives on the same
frequency. On duplex channels, your transceiver transmits on one
frequency and receives on another frequency. You may communicate
with shore stations on both simplex and duplex channels, but because of
the frequency offset, you cannot communicate with other vessels on a
duplex channel.
Channel 16 is the International Distress, Safety and Calling channel.
All vessels equipped with VHF transceivers are required to monitor
channel 16.