Old system. In grade 11 you learnt about the previous maritime distress and safety system which applied to all vessels upon the high seas. According to the system:

• all passenger vessels and cargo vessels of 1600 gross tons and above had to maintain a continuous radio telegraphy (morse) watch on 500 kHz; and
• all passenger ships and cargo vessels of 500 gross tons and above had to maintain a continuous radio telephony watch on 2182 kHz and channel 16.

New system. With the advances in communications technology, this system has now been replaced by a new system which makes the 500 kHz morse system redundant.

• unlike the previous system, GMDSS is automated and provides ship to ship and ship to shore alerting; and
• applies to all passenger vessels and to cargo vessels of 300 grass tons and above on international voyages.