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NavalAIS: How Ships See Each Other
Twenty flashcards on the Automatic Identification System, the Coast Guard's digital radio picture of every ship around you.
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20 cards
- What is AIS?
- A maritime navigation safety communications system standardized by the ITU and adopted by the IMO.
- What does AIS send out automatically?
- The vessel's identity, type, position, course, speed, navigational status and other safety data, to shore stations, ships and aircraft.
- How many reports per minute can AIS handle?
- Well over 4,500, with updates as often as every two seconds.
- On which radio band does AIS work?
- The VHF maritime band, acting like a shipboard transponder.
- Which technology keeps ship-to-ship AIS reliable at that rate?
- SOTDMA: Self-Organizing Time Division Multiple Access.
- What can you read by hovering over an AIS icon?
- Ship name, course and speed, classification, call sign, registration number and MMSI.
- How does AIS change a radio call to another ship?
- You can call it by name instead of "ship off my port bow."
- Which commercial self-propelled vessels need a Class A AIS?
- Those 65 feet or more in length engaged in commercial service.
- Which towing vessels need a Class A AIS?
- Those 26 feet or more in length with more than 600 horsepower, in commercial service.
- Which passenger vessels need a Class A AIS?
- Self-propelled vessels certificated to carry more than 150 passengers.
- Who may use a cheaper Class B AIS instead?
- Fishing industry vessels, among others, if no outside pilot directs them.
- When must AIS be running?
- At all times underway or at anchor and, if moored, at least 15 minutes before getting underway.
- If AIS is switched off for safety or security, what then?
- Turn it back on as soon as possible; log the time and reason and report them to the nearest Captain of the Port or Vessel Traffic Center.
- In what language are AIS safety text messages sent?
- English, and only for navigation safety information.
- Does AIS replace whistle signals, lights or the bridge radio?
- No; the vessel still follows the collision rules and radio rules.
- Where must the AIS pilot plug be?
- Easy to reach from the main conning position, within 3 feet of a 120-volt outlet.
- By when did vessels newly covered by the rule have to install AIS?
- No later than March 1, 2016.
- What number identifies a ship on AIS?
- An official 9-digit MMSI; U.S. ones start with 338, 366, 367, 368 or 369.
- Should AIS be the main way to send a distress alert?
- No; AIS messages and AIS man-overboard devices are not monitored as GMDSS alerts, so use DSC and other distress gear.
- Can AIS be spoofed?
- Yes; it is an open, unencrypted radio system, so trust but verify and never rely on it alone to avoid collisions.
Official sources
U.S. Coast Guard, via eCFR
33 CFR 164.46: Automatic Identification System
U.S. Coast Guard Navigation Center (NAVCEN)
Automatic Identification System (AIS) Overview
U.S. Coast Guard Navigation Center (NAVCEN)
AIS Frequently Asked Questions
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