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)
v. 1.5.1 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.
Version 1.5.1: April 2024: Added ship categories. Minor corrections.