Using a decent HF Ham Radio you can tune to just about any HF frequency and listen in, so there is more than just other Hams to hear. You are not permitted to transmit on the frequencies using an Amateur Radio transceiver and (in the UK at least) if you do have a suitable transceiver you must be licensed to use Maritime SSB.
The primary use for SSB radio at sea is for Safety and although satellite communications cover the whole world they are still quite expensive to use, SSB radio once installed is free to use and can be used for both voice and data communisations (yes you can even send and receive email with the right set up) If you have a receiver cable of tuning in to the Maritime Frequencies, you might hear ships on the Calling/Distress Frequencies. Note that ranges are approximate and are for guidance only, the actual milage will vary depending on conditions. If you do hear a mayday try not to screw up taking down the details 🙂
Maritime Distress and Calling Frequencies
|Band||Voice Frequency (KHz)||DSC Frequency (KHz)||Daytime Range (NM)||Nighttime Range (NM)|
|VHF||156800 (Ch 16)||156525 (Ch 70)||30||30|
Weather – requires software to decode. Either on a PC or iPad/Android tablet.
|Mode||Frequency (kHz)||Tune To (kHz)||Notes|