At regular intervals on 518 kHz NAVTEX messages are transmitted by various coast stations.
NAVTEX stands for (NAVigational TEXt messages). This radiotelex service transmits navigation and meteo warnings and Search and Rescue messages.
Of course you can use a dedicated NAVTEX receiver but if you have a general receiver that can be tuned to 518 kHz in SSB, than you can receive and decode NAVTEX messages.
My FT450 is capable of receiving this frequency. I used a simple magnetic loop antenna
made of 11 turns of wiring around 4 nails inside the attic roof. This antenna using a 150 pF variable capacitor is capable of receiving 470-520 kHz (includes the 600 m ham band).
NAVTEX uses the AMTOR FEC mode. This code is supported by MultiPSK.
The NAVTEX coast stations not too far from my QTH could be received and decoded (Oostende, Dutch coastguard). In the UK, Grimeton there is also a NAVTEX transmitter.
The coaststations transmit in a tight schedule, every 10 minutes another station takes over the transmission.
Also, find below the comments of Jan, PA3ABK with tips for additonal software capable of decoding NAVTEX information/signals.