How to Find a Ship’s MMSI Number and Track It Live
In this article 8 sections
An MMSI number is the nine digits that tell a radio, a satellite, or a tracking site exactly which vessel it is listening to. Everything else about a ship can be ambiguous names get recycled, sister ships get confused for each other, a fleet of forty near-identical bulk carriers can share three words between thebut the MMSI does not collide, not within the same stretch of time, not by accident.
Most people searching this term want one of two things. Either they own a boat and a VHF radio that keeps asking for an MMSI it does not have, or they have somebody else’s ship and want to find it on a map without guessing at the spelling of its name. This guide covers both, though the second half is shorter, because MarineRadar does not issue MMSI numbers. It reads them.
What an MMSI Number Actually Is
MMSI stands for Maritime Mobile Service Identity: a nine-digit number assigned to a vessel’s radio equipment under international telecommunications rules. AIS transponders and DSC-equipped VHF radios broadcast it automatically. It turns up on every tracking site and in every digital radio call without anyone typing it in by hand.
- A Digital Selective Calling radio uses it to ring one specific vessel directly, skipping every other radio on the same channel.
- An AIS receiver uses it to tell one ship’s data stream apart from the next one’s, even with forty vessels broadcasting from the same stretch of water at once.
- A tracking site uses it as the row key behind the scenes, the way a license plate reader keys off a plate rather than a car’s paint colour.
The number is not decorative.
MMSI vs. IMO Number vs. Call Sign
Ships commonly carry three separate identifiers, and mixing them up is the most common mistake in this whole subject.
| Identifier | Length | Assigned by | Changes when |
|---|---|---|---|
| MMSI | 9 digits | National telecom/maritime authority, via the radio licence | Reflagging, resale, or a new radio licence |
| IMO number | 7 digits | Set at build, via class society and registry | Never fixed for the hull’s working life |
| Call sign | Letters and digits, format varies by flag | National telecom authority | Reflagging |
The IMO number is the one identifier that survives everything a ship goes through: a sale, a repaint, a new name, a new flag. That permanence matters for tracking a specific hull rather than whatever name happens to be painted on the bow this year, a distinction our guide to what a cargo ship actually is runs through in more detail.
Reading the First Three Digits
The first three digits of an MMSI are the Maritime Identification Digits (MID), assigned by country. They show who flagged a vessel before you look at anything else.
- 366-369: United States
- 232-235: United Kingdom
- 563: Singapore
- 477: Hong Kong
- 636: Liberia, the largest open ship registry by tonnage
So many of the largest container ships carry an MMSI starting with 636, even though they have never called at a Liberian port.
The MID says nothing about ownership or trade. A Greek-owned, Philippine-crewed bulk carrier can fly a Liberian or Panamanian flag and carry the matching prefix, because flag registration is a legal and financial choice, separate from where a ship actually works.
It also means two unrelated ships can have near-identical MMSIs without any connection. A Liberian bulker and a Liberian container ship built decades apart both start with 636 simply because they share a registry, like two cars from the same state sharing a plate prefix.
The six digits after the MID are what separate one hull from the next, assigned in sequence as each vessel’s radio licence is issued.
How to Find a Ship's MMSI Number
If a ship is already open on a tracking site, its MMSI is in the vessel details, next to the IMO number and call sign. The harder case is starting with only a name, a photo, or a port call mentioned elsewhere.
Starting from a name
- Search the name on a live AIS map first. Most names are distinctive enough that the top result is correct, and the MMSI is on that ship’s page.
- If two vessels share a name (common with older tankers and bulk carriers that have been renamed and resold), cross-check the flag, vessel type, and roughly where it should be. The wrong one usually falls away.
Starting from a photo
- The MMSI is not painted on the hull. The IMO number is, because SOLAS regulation XI-1/3 requires it. A dockside photo will give you a seven-digit number, not a nine-digit one.
- Port agents and class society records also index by IMO number.
- So search the IMO number first, and the MMSI will turn up afterward.
If You Need an MMSI Number for Your Own Boat
Many people searching this term want an MMSI for their own boat, usually because a new VHF radio keeps asking for one. MarineRadar has no part in issuing them.
United States
- Recreational boaters can get one free through BoatUS or Sea Tow, if the vessel stays in domestic waters and never transmits internationally.
- If you cross a border by boat, or carry an EPIRB, the number must come from the FCC directly, with a modest application fee.
United Kingdom
- Ofcom issues them through the Ship Radio Licence.
Most other countries
- A national telecoms or maritime authority hands out blocks of MIDs, and a registry or retailer issues individual numbers against them.
None of this paperwork touches a tracking site. A tracking site only reads what a radio already has.
How to Track a Ship by Its MMSI Number
Once you have the number someone else’s, from a listing, a document, or a radio log turning it into a position takes under a minute.
Step 1: Get the MMSI number
Pull it from a ship listing, a bill of lading, a radio log, or the vessel’s own page if you found it by name first. Write down all nine digits; dropping or transposing one is the single most common reason this search comes back wrong.
Step 2: Open MarineRadar’s live map
MarineRadar pulls AIS from both coastal receivers and satellites, so a ship stays visible whether it is hugging a shoreline or three days from the nearest coast.
Step 3: Paste the MMSI straight into the search bar
No separate MMSI field exists, and none is needed. The same search bar that takes a ship name also takes an MMSI or an IMO number, and a nine-digit MMSI resolves to exactly one vessel every time, which a name search cannot promise.
Step 4: Confirm it is the vessel you expected
Check the name, flag, and vessel type against whatever document sent you looking in the first place. A transposed digit in the MMSI usually returns a different real ship rather than an error. This step catches that kind of typo; the search box on its own never will.
Step 5: Follow it from there
Once the ship’s page is open, position, speed, course, destination and track history are all sitting there, and a zone alert will tell you when it crosses into a port or region you care about without you checking back every hour.
Why an MMSI Search Beats a Name Search
Ship names get reused constantly, and large fleets make it worse rather than better. MSC alone runs a few hundred vessels through a relatively small pool of recurring names; its own ship tracking guide spends an entire section just separating cargo vessels from cruise ships that share the same three letters. CMA CGM has the same problem in miniature, covered from a different angle in the CMA CGM ship tracking guide: name a ship after a place or a historical figure, and sooner or later a different owner names a different hull the same thing. A name is a label, picked by a marketing department and occasionally reused. An MMSI is a key, and two active ships carrying the same one at once means a decommissioning went unrecorded or a registry made an administrative error, both rare enough that a tracking site or a coast guard treats an MMSI match as close to certain.
What a Changed MMSI Looks Like, and Why It Happens
An MMSI is tied to a radio licence, not welded to the hull the way an IMO number effectively is. Sell a ship into a new flag state and the new owner typically applies for a new radio licence under that flag, which usually means a new MID prefix and, often, an entirely new MMSI. The IMO number does not move. The MMSI does.
Serious vessel research treats the IMO number as the anchor for that reason, and the MMSI only as the current, working identifier, not a permanent one. That distinction matters most once a hull has changed hands a few times, which happens constantly in the secondhand tanker and bulker markets.
Old MMSIs do not always disappear cleanly, either. A number freed up after a ship is scrapped can sit unused for years before a registry reissues it to an unrelated vessel, so a historical AIS record searched by MMSI alone can occasionally surface the wrong ship’s track spliced onto the right one’s. Cross-checking the IMO number against the dates in question is the only reliable way to catch this, and it is worth doing before trusting any MMSI-only history that stretches back more than a decade.
MMSI Numbers That Are Not Ships at All
Not every nine-digit MMSI belongs to a vessel, and typing one of these into a ship search explains a surprisingly common complaint that the tracker is broken.
- Two leading zeros: a coast station, not a ship.
- One leading zero: a group call meant for an entire fleet rather than one hull.
- Leading 111: search-and-rescue aircraft.
- Leading 98 or 99: a tender or a fixed aid to navigation, not anything moving under its own power.
None of these throw an error. They return whatever that code is registered to, which is often a lighthouse buoy or a rescue helicopter. The confusion that follows is almost always someone assuming every nine-digit number has to be a ship.
Who Actually Uses This
Marine surveyors and insurers use MMSI lookups to confirm a vessel’s identity against a policy document before a claim goes anywhere. Researchers tracking fleet movements over months lean on the IMO-to-MMSI relationship precisely because the MMSI drifts and the IMO does not, and radio operators test Digital Selective Calling against a known MMSI before trusting it in an actual emergency the one use case here where getting the number wrong has consequences beyond a wasted search. Then there is the more casual case: someone watches an unfamiliar grey hull pass offshore, reads its MMSI off a handheld AIS receiver, and wants to know what it actually is. Warships complicate that particular search, as the navy ship tracking guide covers in detail. Plenty of naval vessels broadcast AIS only intermittently, by choice, and no MMSI lookup works around a transponder that has simply been switched off.
Conclusion
An MMSI number stops being a mystery once you know what the nine digits are doing: three for a flag, six for the vessel, broadcast automatically by a radio that was never asked to keep it quiet. Finding somebody else’s takes a search bar. Getting your own takes a form with a national regulator, not a tracking app.
MarineRadar is free to start on Android and iPhone. Paste in an MMSI you already have, or a ship name if that is all you have got, and the ship’s page does the rest.
FAQs
What is an MMSI number?
A nine-digit radio identity, broadcast automatically by AIS.
How can I get an MMSI number?
Recreational boaters in the US get one free through BoatUS or Sea Tow, provided the vessel never leaves domestic waters and never needs to transmit internationally. Cross a border by boat, or fit an EPIRB, and the application has to go through the FCC directly instead, with a small fee attached. Everyone outside the US applies through their own national telecoms or maritime authority, since in most countries the MMSI is issued alongside the vessel’s radio licence rather than handed out on its own.
How much does it cost to get an MMSI number?
Free for most US recreational boats through BoatUS or Sea Tow. Expect a modest licensing fee elsewhere, since in most countries the MMSI comes bundled with a ship radio licence.
How do I find my vessel's MMSI number?
Check the registration confirmation from whoever issued it, the card that came with a DSC-equipped VHF radio, or the radio’s own settings menu, where the programmed MMSI is usually stored.
Does an MMSI number change if a ship is sold?
Often, yes. A new owner under a new flag typically applies for a new radio licence, which usually means a new MID and a new MMSI, even though the ship’s IMO number stays exactly the same for the rest of its working life.
Can I track any ship using just its MMSI number?
Yes. Paste the full nine digits into MarineRadar’s search bar the same way you would search a ship name, and it resolves straight to that vessel’s live position, assuming it is currently transmitting AIS.
Can I use VHF without MMSI?
For voice calls, yes. The one-button distress call will not work without an MMSI programmed in.
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