Navigation Center
United States Coast Guard
U.S. Department of Homeland Security

AIS Frequently Asked Questions

  1. What is AIS?
  2. How do I register (obtain an MMSI), install, encode, and verify my AIS?
  3. What is the AIS rule and are there alternatives to the rule for small businesses?
  4. Do AIS Class B devices meet current USCG AIS carriage requirements? What are the differences between AIS Class A and Class B devices?
  5. How does AIS help to increase security (and what is NAIS)?
  6. When must AIS be in operation?
  7. Does the installation of the AIS require additional equipment in order for the AIS to operate properly?
  8. Will it be necessary to have electronic navigational charts for use with the AIS?
  9. Are fishing vessels subject to AIS carriage, and, are onboard Vessel Monitoring Systems (VMS) an acceptable substitute for AIS?
  10. Why have some AIS units stopped broadcasting valid position reports?
  11. Why am I unable to see an AIS vessels' name or other static information (dimensions, call sign, etc.)?
  12. Why do I sometimes see more than one vessel with the same MMSI or vessel name (i.e. NAUT)?
  13. Does LED lighting affect AIS?
  14. What are the differences between AIS Class A and B devices?
  15. Is the USCG considering expanding AIS carriage to other vessels or outside of VTS areas?
  16. How can I get a copy of an AIS presentation I saw or heard about? You can download recent presentations given by the Coast Guard Office of Navigation Systems?
  17. Where can I get AIS data?
  18. Can I use AIS to mark nets, pots, traps, moorings, offshore platforms, rigs, or as a race marks, etc.?
  19. What is AIS Channel Management?
  20. Can I use AIS in an emergency or for distress messaging?
  21. What are AIS Aton and AIS Aids to Navigation Reports?
  22. Can AIS be hacked or spoofed? What should I do if I encounter ghost AIS targets?
  23. Have an AIS question not answered here?

1. What is AIS? Per 33 CFR §164.46(a), AIS is a maritime navigation safety communications system standardized by the International Telecommunication Union (ITU) and adopted by the International Maritime Organization (IMO) that provides vessel information, including the vessel's identity, type, position, course, speed, navigational status and other safety-related information automatically to appropriately equipped shore stations, other ships, and aircraft; receives automatically such information from similarly fitted ships; monitors and tracks ships; and exchanges data with shore-based facilities. Note, many devices are marketed as AIS, but, only those (see Types of AIS) that are certified to meet stringent standards are. Read more on what it is, how it works, what it broadcasts, and, the messages it uses, etc.

2. How do I register, encode, install, verify my AIS or, obtain or update an MMSI? AIS devices are not registered, but must be operated with an official 9-digit Maritime Mobile Service Identity (MMSI) number assigned to the vessel and its owner. To learn about, obtain, transfer, or update one see our MMSI page. Encoding an AIS varies by class. Per FCC Regulations (47 CFR 80.231), U.S. sold AIS Class B devices are not user configurable. AIS Class A are, but their static data is password protected. Class B owners, and users who have forgotten their password, should contact their AIS installer, manufacturer, or retailer for instructions on how to reprogram it.

Note, each USCG type-approved AIS has an internal built-in integrity tester that mitigates the need to send TEST text messages to verify its operations. That said, the U.S. Coast Guard operates a Vessel Information Verification Service which can be used to not only verify that your AIS has broadcasted, but, will also highlight any potential static data or encoding discrepancies (contrary to our USCG AIS Encoding Guidance). VIVS is a NAVCEN service that cross-references broadcasted  AIS static data--MMSI, vessel name , call sign, official number, dimensions, draft, and, ship type--received (within the last 30 days) by NAIS with data available from other authoritive sources (i,e, IMO, FCC Universal Licensing service, National Vessel Documentation Center) and highlights any discrepancies.

Note, per 33 CFR §164.46(a)&(d)) vessels equipped with AIS must ensure it is:broadcasting accurately, installed taking into consideration the guidelines developed by the International Maritime Organization (IMO Safety of Navigation Circular.227, Guidelines For The Installation Of A Shipborne Automatic Identification System) or the  National Marine Electronics Association (NMEA 0400-4.00), and, maintained in effective operating condition (per 33 CFR §164.46(d)). Failure to do so could subject one to civil penalties (46 U.S.C. 70119). Thus users are encouraged to routinely innspect their AIS using our USCG Inspection Checklist.

3. What is the AIS rule and are there alternatives to the rule for small businesses? The U.S. Coast Guard has developed rules applicable to both U.S. and foreign-flag vessels that require owners and operators of most commercial vessels operating on U.S. navigable waters to be outfitted with an Automatic Identification System (AIS). These rules are part of our domestic and international effort to increase the security and safety of maritime transportation. Initial AIS rules became effective on July 1st, 2003 (68 FR 60559) and were subsequently amended on January 30th, 2015 (80 FR 5281), so as to require that all vessels denoted 33 CFR § 164.46(d) be outfitted with a USCG type-approved [see Coast Guard Maritime Information Exchange (CGMIX) EQList Search, Select: Approval Series Name—Shipborne AIS] and properly installed operational AIS no later than March 1st, 2016. There are no alternatives to this rule, however, many small business may meet the carriage requirement by purchasing a lower cost AIS Class B device in lieu of a Class A. See our Small Entity Compliance Guide to AIS and our AIS FAQ#4 below for further information.

4. Do AIS Class B devices meet current USCG AIS carriage requirements? What are the differences between AIS Class A devices and Class B devices? Yes, a select segment of mandatory AIS users (see 33 CFR § 164.46(b)(2)) can use a Coast Guard type-approved AIS Class B device in lieu of a Class A device—AIS Class A vs B comparison. Note, U.S. AIS carriage requirements can only be met by USCG type-approved equipment which displays a USCG 165.155/156 Approval Number.  A listing of all USCG type-approved equipment can be found at the Coast Guard Maritime Information Exchange (CGMIX) [EQList Search, Select: Approval Series Name--Shipborne AIS]. Voluntary AIS users may avail themselves of either a AIS Class A or B device, but, such a device must be FCC certified for its use in the United States. For a listing of FCC certified AIS equipment use the FCC OET Equipment Authorization Search Form [Select: Equipment Class--AIS).

5. How does AIS help to increase security (and what is NAIS)? Although AIS is primarily and foremost a navigation tool for collision avoidance, the Coast Guard believes that the AIS will improve security also. AIS and our Nationwide AIS Project (NAIS) increases the Coast Guard’s awareness of vessels in the maritime domain, especially vessels approaching U.S. ports. The AIS corroborates and provides identification and position of vessels not always possible through voice radio communication or radar alone.

6. When must AIS be in operation? Per 33 CFR 164.46(d), vessels required to have AIS must operate it in U.S. navigable waters (as defined in 33 CFR 2.36) at all times that the vessel is navigating (underway or at anchor) and at least 15 minutes prior to unmooring. Should continual operation of AIS compromise the safety or security of the vessel or where a security incident is imminent, the AIS may be switched off. This action and the reason for taking it must be reported to the nearest U.S. Captain of the Port or Vessel Traffic Center and recorded in the ship's logbook. The AIS should return to continuous operation as soon as the source of danger has been mitigated. Note, vessels equipped with AIS--either by mandatory carriage or voluntarily--must abide by the requirements set forth in 33 CFR 164.46 which state an AIS must be: properly installed, use an officially assigned MMSI, that its data be accessible from the primary operating position of the vessel, and, always be in effective operating condition; which entails the continuous operation of AIS and the accurate input (see USCG AIS Encoding Guide) and upkeep of all AIS data parameters. Although Coast Guard AIS authority (46 USC 70114) does not extend beyond U.S. navigable waters or to all voluntary users, mariners are reminded that Navigation Rule 7 requires that every vessel use all available means to determine risk of collision. AIS is one of the most effective means currently available, particularly when coupled with radar and sight, to not only determine the risk of, but, also mitigate collisions. Thus the Coast Guard exhorts all AIS users to maintain their AIS in effective operation, at all times.

7. Does the installation of the AIS require additional equipment in order for the AIS to operate properly? No, however, Chapter V, Regulation 19 of the Safety of Life at Sea Convention (SOLAS), as stated in 33 CFR § 164.46(d)(2), does require certain vessels on international voyage to interface it to other existing onboard equipment (i.e. transmitting heading device, gyro, rate of turn indicator); domestic vessels, are not currently required to do so, however it is highly recommended.

8. Will it be necessary to have electronic navigational charts for use with the AIS? Eventually. Section 410 of the Coast Guard and Marine Transportation Act of 2004 (P.L.108-293, H.R. Rpt. 108-617) directs the Coast Guard to prescribe regulations that will require most commercial vessels "while operating on the navigable waters of the United States...be equipped with and operate an electronic charts"; and that AIS be integrated with the chart display. A rulemaking implementing this additional requirement is in development. Till these regulations are finalized, AIS is not required to be displayed on an ECS or other external display system; although it is highly recommended. The full benefits of AIS are only achieved when it is fully integrated and displayed on other shipboard navigation systems (e.g. Electronic Charts Data & Information System (ECDIS), Electronic Chart Systems (ECS), Radar, Automatic Radar Plotting Aid (ARPA), Tracking Devices, personal software, etc.).

9. Are fishing vessels subject to AIS carriage, and, are onboard Vessel Monitoring Systems (VMS) an acceptable substitute for AIS? Yes and no. Commercial self-propelled fishing vessels of 65 feet or more in length are subject to AIS carriage requirements; see 33 CFR 164.46(b). Per 33 CFR § 164.46(b)(2), fishing industry vessels (i.e. fishing processors, tenders, and vessels as defined in 46 U.S.C. 2101) may use lower-cost AIS Class B units in lieu of Class A devices. However, a NOAA Vessel Monitoring Systems (VMS) are not an acceptable substitute for AIS because they are not inter-operable or compatible. Each uses different communication systems, protocols, reporting rates, and, most importantly VMS does not, nor is it designed to, mitigate collisions or enhance users’ situational awareness. Read more...

10. Why have some AIS units stopped broadcasting valid position reports? On February 27th, 2008 the GPS constellation increased to 32 satellites (PRN 32) thus providing a 5% increase in satellite availability and DOP (dilution of precision) world-wide. It has come to our attention that some (non-USCG type approved) AIS units-particularly old equipment which is non-compliant with the GPS interface standard (IS-GPS-200)-cannot recognize this additional satellite and subsequently are unable to calculate a position and broadcast a valid AIS Position Report. Note, the reported malfunctioning units do continue to receive position reports and are able to send and receive AIS text messages. Owners of AIS equipment denoted here, however, should be aware that their internal GPS systems may not act as a proper-timing or position-back-up under certain circumstances, i.e. when in view of PRN32. AIS users must ensure their units have or are interfaced with a properly operating Electronic Position Fixing System at all times. GPS and/or AIS problems should be reported via the NAVCEN website or via phone to the USCG Navigation Information Service at 1-703-313-5900.

11. Why am I unable to see an AIS vessels' name or other static information (dimensions, call sign, etc.)? Shipboard AIS units autonomously broadcast two different AIS messages: a 'position report' which includes the vessels dynamic data (e.g. latitude, longitude, position accuracy, time, course, speed, navigation status); and, a 'static and voyage related report' which includes data particular to the vessel (e.g. name, dimensions, type) and regarding its voyage (e.g. static draft, destination, and ETA). Position reports are broadcasted very frequently (between 2-10 seconds-depending on the vessels speed-or every 3 minutes if at anchor), while static and voyage related reports are sent every six minutes; thus it is common and likely that an AIS user will receive numerous position reports from a vessel prior to receipt of the vessel's name and type, etc. Note, the U.S. Coast Guard operates a Vessel Information Verification Service which can be used to not only verify that an AIS has broadcasted, but, will also provide certain AIS static data (i.e. MMSI, name, call-sign, IMO number, vessel type, draft, dimensions, and positioning source) and highlight any potential data or encoding discrepancies (contrary to our USCG AIS Encoding Guidance) the vessel may have.

12. Why do I sometimes see more than one vessel with the same MMSI or vessel name (i.e. NAUT)? AIS users are required to operate their unit with a valid MMSI, unfortunately, some users neglect to do so (for example, use: 111111111, 123456789, 00000001, their U.S. documentation number, etc). A valid MMSI will start with a digit from 2 to 7, a U.S. assigned MMSI will start with either 338, 366, 367, 368, or 369. AIS users whom encounter a vessel using MMSI: 1193046 or named: NAUT should notify the user that their AIS unit is broadcasting improper data; see Nauticast AIS-MMSI Technical Bulletin for further information. All AIS users should check the accuracy of their AIS data prior to each voyage, and, particularly units that have been shutdown for any period of time. NOTE: If you are receiving (in range of) AIS reports from vessels using the same MMSI, they will appear as one vessel (jumping from position-to-position or line-to-line) on a graphical screen (e.g. ECS, ECDIS, radar) or on the AIS Minimal Keyboard Device (MKD). Note, the U.S. Coast Guard operates a Vessel Information Verification Service which can be used to not only verify that an AIS has broadcasted, but, will also provide certain AIS static data (i.e. MMSI, name, call-sign, IMO number, vessel type, draft, dimensions, and positioning source) and highlight any potential data or encoding discrepancies (contrary to our USCG AIS Encoding Guidance) the vessel may have.

13. Does LED lighting affect AIS? Yes, LED lighting may interfere with your AIS and other VHF radios. See our USCG Safety Alert 13-18 for further information and how to test whether they do.

14. What are the differences between AIS Class A and B devices? See a comparison of AIS Class A and Class B devices here.

15. Is the USCG considering expanding AIS carriage to other vessels or outside of VTS areas? Notwithstanding that the Coast Guard strongly encourages the use of AIS, we have no plans to expand AIS carriage beyond our current regulation, 33 CFR 164 (68 FR 60599 as amended by 80 FR 5281 as published, 80 FR 17326 as corrected, 80 FR 20250 effective date), which required AIS carriage and it’s use on most commercial self-propelled vessels operating on U.S. navigable waters as mandated by the AIS requirements of Regulation V/19.2.4 of the Safety of Life at Sea Convention and Sec. 102 of the Maritime Transportation Security Act of 2002 (46 U.S.C. 70114). Comments submitted, supporting documents, and the regulatory analysis to this and our proposed rulemaking (73 FR 76295) can be found at www.regulations.gov [Search: USCG-2005-21869]. See printer-friendly PDF formats of these 2015 requirements, our 2008 proposed rule, an amalgamation of both, our 2003 requirements (68 FR 60599), and, a chart-comparison of all three.

16. How can I get a copy of an AIS presentation I saw or heard about?

Presentations given by the Coast Guard Office of Navigation Systems:

17. Where can I get AIS data? Local, state and federal government agencies can request real-time or historical U.S. Coast Guard Nationwide AIS (NAIS) data on our NAIS Data Request page. Some NAIS historical data is also publically available at MarineCadastre.gov. Although, the U.S. Coast Guard does not make our NAIS data readily available to the general public or to commercial purveyors, we do operate a Vessel Information Verification Service which can be used to obtain certain AIS static data (i.e. MMSI, name, call-sign, IMO number, vessel type, draft, dimensions, and positioning source), and highlights any potential data or encoding discrepancies (contrary to our USCG AIS Encoding Guidance), of vessels in the NAIS database.

18. Can I use AIS to mark nets, pots, traps, moorings, offshore platforms, rigs, or as a race marks, etc.? There are no outright prohibitions to use AIS (i.e. AIS AtoN) as a marker (see Types of AIS, RTCM 12110.0 for AIS Mobile Aids for Navigation Stations, and IALA Recommendation 1016 – Mobile Marine Aids to Navigation). However, it is not permissible to do so with equipment intended for use on vessels, (i.e. AIS Class A or B devices), for lifesaving (i.e. AIS SART, MOB AIS, EPIRB AIS), or with devices that are not FCC certified and licensed. See 47 CFR §§ 2.803, 2.805, 2.301, and 80.13 regarding licensing, station identity, and the prohibition to sell, market, or use radio devices that are not FCC authorized (search, Equipment Class: AIS). Also, see FCC Enforcement Advisory Public Notice DA-18-1211.

19. What is AIS Channel Management? One of the lesser known and potent features of AIS is its ability to operate on multiple channels of the VHF-FM marine band. This frequency agility ensures AIS can be used even when the default channels are otherwise unavailable or compromised. In such conditions, competent authorities, such as the Coast Guard, can use an AIS base station to tele-command shipborne AIS devices to other more appropriate channels when within a defined region(s) of 200 to 2000 square nautical miles. This can be done automatically (and without user intervention) by receipt of the AIS channel management message (AIS message 22) or manually entered via the AIS Minimal Keyboard Display (MKD) or similar input device. Once commanded or inputted the channels management information will stay in memory for 5 weeks or until a vessel exceed 500 nautical miles from the defined region. AIS channel management commands can only be automatically overridden via another channel management message for the same defined region or manually overridden or erased by the user via the unit’s channel (regional frequencies) management function—read more. Note, reinitializing or resetting your AIS or transmission channels will not necessarily reprogram your unit back to default channels.

20. Can I use AIS in an emergency or for distress messaging? Although not prohibited (see 33 CFR § 164.46(d)(3)), be aware that AIS safety related text messages nor AIS locating devices (i.e. AIS MOB devices)are not currently monitored or acted upon as Global Maritime Distress Safety Systems (GMDSS) alert messages by the Coast Guard Rescue 21 or other maritime search and rescue authorities or systems. Therefore, AIS should not be relied upon as the primary means for broadcasting distress or urgent communications, nor used in lieu of GMDSS devices such as Digital Selective Calling (DSC) radios which are designed to process distress messaging. Nonetheless, AIS remains an effective means to augment GMDSS and provides the added benefit of being seen by other AIS users and USCG assets within AIS radio range, in addition to being heard via AIS text messaging. For further guidance, see USCG Safety Alert 5-10. Also, see the International Maritime Organization’s (COMSAR) Circular 46, Use Of AIS Safety-Related Messaging In Distress Situations.

Consumers interested in Man Overboard (MOB) or Personal Locating Beacon (PLB) devices should pay particular attention to their mode of operation, i.e. sole DSC distress alerting, sole AIS transmitters, dual AIS-DSC, or as private network devices. Owners of any AIS locating or DSC alerting devices should ensure they are well maintained, at the ready, and, stored or fitted in such a manner that mitigates their accidental activation. Inadvertent activations should be reported immediately to the pertinent Coast Guard District or Regional Command Center.

21. What are AIS Aton and AIS Aids to Navigation Reports? AIS Aids to Navigation (Aton) Stations are shore or mobile AIS stations, identified by a 99yyyxxxx MMSI, which report (AIS message 21) the location and status of an aid to navigation (ATON). Which can be done from the ATON it resides on or from elsewhere, i.e. ashore from another nearby ATON. They can also produce virtual, electronic ATON, which do not exist physically, but which can be portrayed on navigational displays (i.e. radar, ECDIS, INS) that our AIS-capable (i.e. IEC 62288 complaint). These stations can also broadcast other pertinent marine safety information, e.g., environmental data, tidal information, navigation or hazardous warnings via Application Specific Messages (message 6/8).

The U.S. Coast Guard and some other approved entities (i.e., U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, Marine Exchange of Alaska, etc.) have been transmitting AIS ATON Reports and marine safety information via AIS since 2014 (see our Special Notice 01-2014). The exact content, location, and times of these transmissions are announced in the Coast Guard Local Notices to Mariners (LNM) and denoted in Coast Guard Light List.

Note, AIS ATON stations operated in the U.S., other than by the U.S. Coast Guard, require Federal Communications Commission (FCC) or National Telecommunication Information Agency (NTIA) radio type-certification and proper licensing, which they will not grant without prior consultation with the U.S. Coast Guard. Requests for approvals to use AIS as or on a Private ATON may be directed to  cgnav@uscg.mil, and must include either a CG Form 2554 or 4143 following these instructions. For a listing of FCC type-certified AIS ATON devices, search Equipment Class--AIS at FCC OET Equipment Authorization Search Form.

For further information on AIS ATON and their uses, please refer to the various IALA Guidelines and Recommendations (i.e., G1062, Establishment of AIS as an AtoN).

22. Can AIS be hacked or spoofed? What should I do if I encounter ghost AIS targets? AIS devices do not inherently have virus or malware protection, so cyber security best practices against hacking should be adhered to if you connect your AIS to a network or update it using removable electronic devices (e.g. USB drives). AIS by design, is an open, non-proprietary, unencrypted, unprotected radio system, intended to operate on non-secure VHF-FM channels. So technically it can be spoofed—so trust, but, verify. Should you encounter ghost or fake AIS targets, please report them to us using our AIS Problem Report.

AIS users are reminded of Navigation Rule 7 which, amongst other things, states that every vessel should use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. AIS while an invaluable situational tool, it should never be solely relied upon for collision avoidance or navigational decision-making.

23. Have an AIS question not answered here? Please contact us.