Guide to International Requirements for Global Maritime Distress and Safety System (GMDSS) Communication Equipment
under the International Convention for Safety of Life at Sea (SOLAS Convention - 2024 Amendments)
v. 1.5 of this guide

Ship Type:
Ship Service:
Gross Tonnage:  
Date Built: Day: Month: Year:
Operational Areas:
Sea Areas:

Does the ship operate in Sea Area A1 - Within range of a VHF coast station with continuous DSC ** alerting?
Yes No

Does the ship operate in Sea Area A2 - Outside Sea Area A1, but within range of an MF coast station with continuous DSC ** alerting?
Yes No

Does the ship operate in Sea Area A3 - Outside Sea Areas A1 and A2, but within coverage of an IMO recognized mobile satellite service?
Yes No

Does the ship operate in Sea Area A4 - Outside Sea Areas A1, A2, and A3?
Yes No

© Radio Technical Commission for Maritime Services (RTCM), 1150 18th St NW Suite 910, Washington, DC 20036 USA
Mail: 2200 Wilson Blvd, Suite 102-109, Arlington VA 22201 USA Email:
* MODU means "Mobile Offshore Drilling Unit."
** DSC means "Digital Selective Calling" -- a technique using digital codes which enables a radio station to establish contact with, and transfer information to, another station or group of stations.

How to use this guide: Enter the description of the ship of interest in the form above. Click on "Display required GMDSS communication systems". The GMDSS communication systems required will appear in a new window. Click the "Calculate another ship" button on the list to return to this page to create a list for a different ship.
Type, Service, and Date Built: As defined by the SOLAS Convention.
Information on Sea Areas: GMDSS Sea Area page - U.S. Coast Guard Navigation Center
GMDSS page - Canadian Coast Guard
About this guide: The GMDSS communication equipment requirements in this guide come from SOLAS Chapter IV, and also non-GMDSS communication requirements in Chapters V and IX-2 of the International Convention for the Safety of Life at Sea (SOLAS), and include the SOLAS requirements up to and including the amendments adopted in 2022, which came into force 1 January 2024.
Comments and Questions:


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Version 1.0: Initial public release - SOLAS requirements
Version 1.1: High Speed Craft Code and MODU Code requirements added. Note on maintenance and duplication of equipment added.
Version 1.2: June 2007: Added Long Range Identification and Tracking (LRIT). Corrected towed/escorted MODU requirements. Removed references to Inmarsat E EPIRBs. Minor errors corrected.
Version 1.3: July 2010: Changed "radar transponder" terminology to "search and rescue locating device" and added references to AIS-SART were just SART appeared.
Version 1.4: January 2021: Changed INMARSAT references to “IMO recognized mobile satellite service”.
Version 1.5: January 2024: Revised to reflect 2024 SOLAS revisions.