There are approximately 250 ITU duplex channels, 125 ITU
simplex channels, 660 ITU FSK channels, and 10 semi/automatic (DSC)
channels used for MF/HF maritime safety communications in the Pacific.
All voice transmissions use USB.
The legal requirement for
SOLAS ships to maintain a voice watch of
emergency frequencies has been replaced with requirement only for a DSC - or digital selective calling
- watch. This is tied in with the
GMDSS system which most countries are now adopting.
GMDSS links shipboard GPS receivers to radio transceivers, allowing one touch of an emergency button to transmit a vessels current GPS location to land and nearby vessels when in distress.
Some countries still maintain a voice watch on
non-DSC (voice only) frequencies for smaller vessels.
Morse Code is no longer used in marine radio. RADPHONE and SEAPHONE services ceased operation in Australia in 2002, replaced by the now much more affordable Inmarsat and Seamail systems.
This resource does not include information for FSK/data channels used for HF weather fax.
You can track some AIS equipped ships online via http://www.marinetraffic.com/ais/
Last Update 1/8/2014