The Global Maritime Distress Safety System (GMDSS) is an
internationally agreed-upon set of safety procedures, types of
equipment, and communication protocols used to increase safety
and make it easier to rescue distressed ships, boats and
GMDSS consists of several systems, some of which are new, but
many of which have been in operation for many years. The
system is intended to perform the following functions:
alerting (including position determination of the unit in
distress), search and rescue coordination, locating (homing),
maritime safety information broadcasts, general
communications, and bridge-to-bridge communications. Specific
radio carriage requirements depend upon the ship's area of
operation, rather than its tonnage. The system also provides
redundant means of distress alerting, and emergency sources of
GMDSS, Global Maritime Distress and Safety Systems, replaced
the marine carriage requirements imposed by the Communications
Act of 1934. Instead of telegraph and simple high frequency
radio communications where you hoped someone was listening, a
highly integrated system of ships and shore based systems with
automatic monitoring systems virtually guarantee your call for
help will be heard. There are many variations in the new
carriage requirements that can seem very confusing at times.
Primary to any GMDSS installation is first identify which
ocean area a vessel will be operating. These are typically
listed as A1, A2, A3 and A4 with A1 being always within VHF
range of shore based stations, 20 to 30 miles, and area A4
being those places where satellite communications are
impossible such as the polar regions. It should be noted that
the requirements are cumulative in nature. An A4 vessel is
also equipped, by definition, with equipment for A1, A2 and A3
Carriage Requirements for GMDSS A1:
A2 (in addition to A1 equipment):
- One VHF radio capable of DSC (Digital Selective
Calling) on channel 70 and voice communications on channel 16,
13 and 6.
- One SART (Search And Rescue Transponder) if under 500
gross tons otherwise two.
- Two approved lifeboat portable VHF radios if under 500
gross tons otherwise two.
- One Navtex receiver or an Inmarsat EGC receiver if
operating in an area where Navtex is not offered.
- One 406 MHz or a 1.6 GHZ satellite EPIRB, (Emergency
Position Indicating Radio Beacon). Note: a VHF DSC
EPIRB may replace the 406 MHz and 1.6 MHz EPIRB if operating
exclusively in area A1.
A3 (in addition to A1 and A2 equipment):
- One MF (Medium Frequency) radio installation capable
of transmitting and receiving on the frequencies 2187.5 kHz
using DSC and 2182 kHz using radiotelephony.
- One DSC watch keeping receiver operating on 2187.5
- One 406 MHz EPIRB. A HF radio installation operating on
working frequencies in the (marine) bands between 1,605 kHz
and 27,500 kHz. (This requirement is normally fulfilled by the
addition of this capability in the MF equipment referred to in
- One Inmarsat C ship earth station.
- One MF radio installation and 2187.5 kHz DSC watch
- One 406 MHz EPIRB.
A4 (in addition to A1, A2 and A3 equipment):
- One MF/HF radio installation capable of transmitting
and receiving on all distress and safety frequencies in the
(marine) bands between 1,605 kHz and 27,500 kHz: using DSC,
radiotelephony and NBDP (Narrow Band Direct Printing
- One MF/HF DSC watch keeping receiver capable of
maintaining DSC watch on 2187.5 kHz, 8,414.5 kHz and on at
least one of the distress and safety DSC frequencies 4207.5
kHz, 6312 kHz, 12577 kHz or 16804.5 kHz at any time. It is
possible to select any of these DSC distress and safety
- One 406 MHz EPIRB.
In addition to the carriage requirements, regulation 15 of the
SOLAS GMDSS regulations defines 3 methods to ensure
availability of GMDSS equipment at sea.
- One MF/HF radio installation as described
- One MF/HF DSC watch keeping receiver as described
- One 406 MHz EPIRB. Note: Satellite based systems do
not operate in the A4 Polar Regions.
Recreational vessels do not need to comply with GMDSS radio
carriage requirements, but will increasingly use the Digital
Selective Calling (DSC) VHF radios and offshore vessels may
elect to equip themselves further. Vessels under 300 Gross
tonnage (GT) are not subject to GMDSS requirements and vessels
from 300 to 500 GT have less restrictive carriage requirements
than vessels 500 GT and over.
- At sea electronic maintenance, requiring the carriage
of a qualified radio/electronic officer (holding a GMDSS First
or Second Class Radio-Electronics Certificate) with adequate
spare parts and service manuals.
- Duplication of certain equipment, or;
- Shore based maintenance contracts. Almost exclusively
vessel operators opt for duplication of equipment or shore
based maintenance contracts.