Class A AIS Technical Specifications: Key Parameters and Installation Standards
As a critical navigational equipment for large ships, the performance and installation quality of Class A AIS directly affect navigational safety and regulatory compliance. This article focuses on the core technical parameters, installation specifications, and inspection requirements of Class A AIS, helping maritime professionals grasp the key points of equipment selection and use.
Technical Parameters of Class A AIS
According to the technical requirements of IMO Res.MSC.74(69) and China MSA's 2025 AIS Operational Inspection Guidelines, Class A AIS must meet the following key parameters:
Transmission Power: 12.5W (main power) / 1W or 2W (auxiliary power), ensuring stable signal transmission within the coverage area;
Communication Protocol: Adopts SOTDMA technology, which divides 4500 time slots per minute to avoid signal interference and realize efficient data exchange;
Data Update Rate: The update interval automatically adjusts according to the ship's navigation status: 2 seconds for ships sailing at over 23 knots (especially when changing course), 6 seconds for ships between 14-23 knots, 10 seconds for ships between 0-14 knots, and 3 minutes for anchored ships;
Message Types: Mainly transmits messages 1, 2, 3 (dynamic information), message 5 (static and voyage information), and supports short message messages 6, 8, 12, 14, etc.;
Positioning Requirement: For Class A AIS installed on domestic navigation ships after November 1, 2022, Beidou navigation technology must be adopted to ensure positioning accuracy and independence <superscript>1;
Power Supply: Dual power supply (main power 220VAC/24VDC + emergency power 24VDC) with automatic switching function (switching time < 1 second) to ensure continuous operation in case of main power failure.
Standard Installation Requirements for Class A AIS
Improper installation of Class A AIS will lead to signal attenuation, positioning deviation, and other problems, affecting its normal operation. The following installation standards must be strictly followed:
Antenna Installation: The AIS VHF antenna should be installed at a high position on the ship to avoid obstruction by metal structures. It should be at least 2 meters away from the ship's VHF radio antenna in the vertical direction; if installed on the same horizontal plane, the horizontal distance should be at least 10 meters. The antenna should be free of excessive rust and peeling, and the cable connection and bulkhead penetration should have good weathertight performance.
Equipment Placement: The AIS display unit should be installed in the bridge where navigators can easily observe and operate it, avoiding direct sunlight and moisture. The host unit should be placed in a well-ventilated area to ensure heat dissipation.
Cable Layout: The antenna cable should be sealed and fixed to avoid damage. The cable length should be minimized to reduce signal loss, and the bending radius should not be less than the specified value.
Information Configuration: The static data (ship name, call sign, MMSI, ship type) configured in AIS must be consistent with the ship's inspection certificate and MMSI certificate. It is strictly prohibited to modify the MMSI code without authorization.
Key Inspection Items for Class A AIS
To ensure the normal operation of Class A AIS, regular inspections are essential. The key inspection items include <superscript>1<superscript>4:
Check whether the equipment certificate is complete and consistent with the actual configuration;
Use the built-in self-test function (BIIT) to verify that the equipment can work normally within 2 minutes after startup;
Verify that the dynamic data of AIS is consistent with other navigational equipment (such as radar, GPS);
Simulate fault conditions (such as GNSS position loss) to check whether the alarm function is normal;
For AIS that has been installed on board for 10 years, a third-party inspection report must be provided during the first periodic inspection; for those installed for more than 15 years, a third-party inspection report must be provided for each periodic inspection.