Maritime guides
Short, exact explanations of the identifiers, signals and terms behind every ship you can look up on Seadar. Each guide is checked against the primary source (IMO, ITU, UNECE, the U.S. Coast Guard) and shows live data from Seadar where it proves the point. Every guide ends in a lookup, so you can go straight from the idea to a real ship.
Identifying a ship
- What is an MMSI number?
The nine-digit number that identifies a ship’s radio, what its digits mean, and why it changes when a ship changes flag.
- What is an IMO number?
A ship’s permanent seven-digit identifier: which ships have one, how the check digit works, and how to check a number.
- IMO number vs MMSI: what is the difference?
The hull’s permanent number against the radio’s changeable one, side by side, with a live example of a ship that switched MMSI.
- What is a ship’s call sign?
The ship’s international radio name: how it is formed, what the prefix tells you, and why it changes with the flag.
AIS and ship tracking
- What is AIS (Automatic Identification System)?
The radio system ships use to broadcast identity and position: who must carry it, what it sends, how often, and its limits.
- How ship tracking works
From a transponder on the bridge to a dot on a map: receivers, satellites, gaps, and why ETAs are often wrong.
- AIS navigational status codes explained
All sixteen status codes, from “under way using engine” to “undefined”, who sets them, and a live count of ships by status.
Ships and their measurements
- Ship types explained: AIS type codes and what they mean
The two-digit AIS type code, what each range and the hazard digit mean, and why a container ship shows up as plain “cargo”.
- Gross tonnage vs deadweight: how ship size is measured
Why a cruise ship has four times the gross tonnage of a tanker that carries ten times the weight.
Flags, ports and sanctions
- What is a flag of convenience?
Why most of the world’s big ships fly the flag of a country their owners are not from, and what that means.
- What is a UN/LOCODE?
The five-character UN code for ports and places, how it is built, and how ships use it in their AIS destination.
- What is the shadow fleet (dark fleet)?
Ships operating to evade sanctions, safety rules or insurance: the IMO’s definition, the warning signs, and what the sanctions lists say.
Check an IMO number or MMSI
Type an IMO number (7 digits) or an MMSI (9 digits). Seadar shows what it is, whether it passes the checks, and finds the ship.
For information only. Not for navigation, and not a substitute for the official sources cited.