I don't know about now, because I've been retired for over ten years, but back
in the 1980s, the international Safety of Life at Sea (SOLAS) treaty began
requiring commercial vessels to have radiotelephone capability in the 2-3 MHz
band. This was to accommodate all the sea going vessels that weren't large
enough to be required to have a radiotelegraph station.

For emergency calls, the transmitter (usually a transmitter-receiver unit) had
to be able to send a two-tone -- fast hi-lo -- transmission on 2182 at the push
of a button. The receiver had to be on watch (constantly monitor) on 2182 to
receive a two-tone transmission.

At least one working channel was required, too, pretty much like in the old
days before the advent of marine VHF.

Bill, K5BY
T2GB0040061