AIS 650 - bearing to the target

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Vin,

Q: service #1. you need an electronic heading device for AIS to tell you the bearing.

I replied: well, the E/127 knows my heading already - it is on the top of the MFD. It reads it from GPS and shows it on the top of the chartplotter. Why do I need another device to have the all-Raymarine (GPS and AIS) system tell me what my heading is?

A: AIS target CPA and TCPA calculations derived exclusively from GPS data (lat/lon, COG, and SOG) from one's own ship and the AIS target. The range and bearing data items specified within the cursor position dialog are designed to report bearings relative to the vessel's position, using north as a reference rather than bearings relative to the vessel's head. As such, the range and bearing data items specified within the cursor position dialog are not dependent upon heading data.
Bearings listed within the Tracked Targets List are specified relative to the vessel's head, as such the requirement for heading exists for this feature. Contrary to your belief that the internal GPS sensor within your MFD is providing the system with heading data (note the Heading data item within your screen snapshot is dashed), it instead providing the system with GPS Course Over Ground (COG). Heading and GPS COG data items can differ significantly in value due to the effects of leeway induced by current and wind. Accordingly, COG may not serve as an accurate bearing referent for this safety feature. Please click here to view a FAQ addressing this subject. As AIS bearings are specified relative (0-180 port (P) / starboard (S)) to the vessel's head, a heading sensing device (Raymarine or third party must be interfaced to the system) to view bearing information within the Tracked Target List.
We generally recommend that an Evolution autopilot's EV-1 Sensor Core component be installed onboard vessels not equipped with heading sensors, as the EV-1 Sensor Core may be included as part of any future Raymarine Evolution autopilot installation ... should there be one ... thereby potentially reducing the cost of a future autopilot installation while providing the system with heading data in the interim.

A feature request will be logged to consider adding AIS target bearing data relative to the vessel's position, using north as a reference. Please click here more information concerning product and feature suggestions..