Ask two vessel owners what GMDSS equipment they need and you often get two different answers — because the honest answer is “it depends on your sea area.” The Global Maritime Distress and Safety System divides the world into four sea areas, A1 through A4, and each one dictates the distress equipment a vessel must carry. Get the sea area right and you fit exactly what you need; get it wrong and you either overspend or fail survey. This guide explains all four, what equipment each requires, and how Singapore-based operators should think about it.
Why sea areas exist
GMDSS is built on a simple idea: a vessel must always be able to raise the alarm using at least two independent means, and the equipment that can reach a rescue coordination centre changes with distance from shore. Close in, VHF works. Further out, you need MF, HF, or satellite. The sea areas map those ranges so equipment rules can follow them.
The four GMDSS sea areas
| Sea area | Definition | Primary distress means |
|---|---|---|
| A1 | Within VHF coverage of a coast station with DSC — roughly 20-30 nm from shore | VHF DSC (Ch 70) |
| A2 | Within MF DSC coverage of a coast station — roughly out to 100-150 nm | MF DSC (2187.5 kHz) |
| A3 | Within geostationary satellite coverage — approximately 70°N to 70°S | Recognised satellite service or HF DSC |
| A4 | The polar regions beyond A3 — above ~70°N and below ~70°S | HF DSC |
Equipment required by sea area
Each area is cumulative — an A3 vessel carries A1 and A2 capability too. The typical fit:
- Sea Area A1 — VHF radio with DSC, NAVTEX receiver, an EPIRB (406 MHz), and a SART or AIS-SART. The lightest fit, suitable for coastal and harbour operation.
- Sea Area A2 — everything in A1 plus an MF radio installation with DSC, and MF/HF DSC watchkeeping. Suited to vessels working the near-continental shelf.
- Sea Area A3 — everything in A2 plus either a recognised satellite terminal (for example an Inmarsat or Iridium GMDSS terminal) or an HF radio installation with DSC. This is the common fit for ocean-going Singapore-flagged tonnage.
- Sea Area A4 — everything above plus HF DSC as the primary means, because geostationary satellites do not reach the poles. Relevant only to vessels trading to high latitudes.
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Where most Singapore vessels sit
The great majority of Singapore-based commercial activity falls into A1 or A2: harbour craft, bunker vessels, coastal supply boats, ferries, and near-shore OSVs. Deep-sea tankers, bulkers, and container ships on international routes are fitted for A3. A4 is rare and applies only to vessels that trade into polar waters. Matching your fit to your genuine operating area — rather than over-fitting to A3 by default — is where owners save real money.
Iridium and Inmarsat both satisfy A3 now
For years, satellite GMDSS meant Inmarsat. Iridium is now also a recognised GMDSS provider, and because its constellation covers the poles it can support even high-latitude operation. For an A3 vessel, the choice between an Inmarsat and an Iridium GMDSS terminal comes down to coverage needs, airtime, and how it sits alongside your primary broadband — a decision we help operators work through case by case.
Common survey issues
- Fitted for the wrong area — an A2 vessel operating on A1 equipment, or vice versa.
- Second means of alerting missing — GMDSS requires two independent means; a single satellite terminal is not enough on its own.
- Battery reserve source — insufficient reserve power for the required hours of operation.
- DSC not programmed — wrong or missing MMSI in the radios.
Get your GMDSS fit right for your sea area
Tell us your vessel type and where it actually operates, and we will specify the correct GMDSS fit for your sea area — VHF, MF/HF, or satellite — with install, MMSI programming, and MPA survey preparation. Sales at Envisiondata Pte Ltd — sales@envisiondatasg.com — or WhatsApp Steve directly on +65 9088 4899.
How we can help
Compliance mistakes usually surface at the worst time: during a survey, a port state inspection or a charterer audit. We help owners get the equipment, licences and paperwork right before that happens.
- Free equipment and licence check for your vessel
- Supply of GMDSS, VHF, EPIRB, SART and AIS equipment
- Installation, programming and survey preparation
- Help with IMDA and MPA application steps
What happens when you contact us
- Short call or meeting — we listen to how your vessels operate.
- Vessel and route review — we check equipment, space, power, contracts and licensing.
- Clear recommendation — a written proposal and SGD quote, with options.
- Install and support — commissioning, testing and ongoing support.
Related: GMDSS sea areas explained
Book a free compliance check
There is no obligation. If your current set-up is already the right one, we will tell you.
About the author
Steve leads Envisiondata Pte Ltd in Singapore. He has more than 20 years in cables, telecom infrastructure and satellite communications across ASEAN. He designs and supports connectivity for tugs, OSVs, harbour craft and commercial fleets across the region.
Written by Steve
Steve has over 20 years of experience in cables, telecom infrastructure and satellite communications across ASEAN. He founded Envision Data to help Singapore and SE Asia vessel operators choose and run the right maritime connectivity, from Starlink and OneWeb to Iridium, Inmarsat and GMDSS.
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[…] China Sea. If you are unsure which band your trading pattern actually puts you in, our breakdown of GMDSS sea areas A1 to A4 and the equipment each requires is the right starting point. Second, spending more on the radio while economising on the antenna […]