Ever wondered what happens behind the scenes when a ship transmits its data?
It turns out, an AIS transceiver doesn't just broadcast one giant data packet. To save bandwidth and optimize transmission, the data is split into three core categories sent at different intervals:
Dynamic Data (The "Real-Time" Info)
This data changes constantly and is broadcasted every few seconds (depending on the vessel's speed and status).
MMSI Number: Like a 9-digit long international maritime phone number, assigned by the flag state and may change with flag or ownership
Navigation Status: At anchor, underway using engine, moored, etc.
Position: Precise Latitude & Longitude.
Speed Over Ground (SOG) & Course Over Ground (COG)
True Heading & Rate of Turn (ROT)
Static Data (The "Identity" Info) & Voyage-Related Data (The "Destination" Info)
Static data and voyage-related data is typically broadcasted every 6 minutes. The static data rarely changes and includes the following information:
IMO Number: A permanent unique identifier linked to the ship's hull (can be empty)
Call Sign: The vessel's radio call sign.
Vessel Name: (e.g., "Ever Given").
Ship Type & Dimensions: Ship Type, dimensions for length and beam
The voyage-related data is manually configured by the crew for each journey and includes:
Draft: How deep the ship sits in the water (crucial for shallow waters).
Destination: Where the ship is heading.
ETA (Estimated Time of Arrival): UTC time of expected arrival.
š” Interesting becauseā¦
Rather clever scheduling: by sending fast-changing dynamic data frequently and static data less often - AIS prevents VHF radio frequencies from getting completely overloaded. Itās a masterclass in efficient maritime communication protocols which was originally implemented for collision prevention.