SailGrib WR can receive AIS data (Automatic Identification System) through the boat NMEA feed or via Internet (if your device is connected to the Internet and the area is covered by AISHub). The app will read the received sentences, display AIS targets on the map and calculate for each of them the Closest Point of Approach (CPA) and warn in case of danger.
The target received and processed by SailGrib WR are the following:
- Class A: Mandatory since 2002 onboard most vessels over 300 tons and since 2014 for fishing vessels over 16 meters. They transmit at 12.5 W. If the propagation is good, you might see targets at over 30 nm.
- Class B installed on pleasure craft. They transmit at 2W for a visibility around 10 nm.
- Aid to Navigation (AtoN): primarily used to transmit the position of navigation marks such as the BXA buoy at ​​the tip of the Gironde in France. The transponder can be physically installed on the device or on land. In such a case, it will have virtual tag.
- AIS SART (Search And Rescue Transmitter): introduced in 2010, the AIS SART individual emergency beacons transmit a signal in case of man overboard. They are now sometimes mandatory for offshore races. We strongly recommend them.
Every AIS target is identified by its MMSI number (Maritime Mobile Service Identity).
AIS Class A and B emit two types of messages:
- “static” data such as vessel name, vessel type, size, destination…
- positions data with among others the coordinates of the ship, its speed and heading.
Static messages are sent every 6 minutes. So you might have targets only identified for a while by their MMSI numbers. SailGrib retains the name attached to each MMSI. The enables the app to quickly identify by name known ships as soon as we receive a position message.
Position messages are transmitted:
- every 2 to 10 seconds depending on its speed for a class A vessel, and every 3 minutes if anchored,
- every 30 seconds for a class B ship whose speed is greater than 2 knots, every 3 minutes otherwise.
As soon as a position message is received, SailGrib calculates the CPA of the target. The CPA can be displayed on the map. If the CPA and the Time at CPA (TCPA) are less than a set limit an alarm can be thrown.
Watch a video of AIS targets in the Solent