[CA] [CA11] Align compass to GPS

[George Bailey]

For an Evolution autopilot, after performing Align Compass to GPS in flat water with no wind or current, heading, COG, and readings off a reliable compass are all within a degree. As I turn from the original direction where the Align function was performed, the Heading and COG begin to diverge, reaching as much as 8-10 degrees when turned 120 degrees off the original course. The heading is the wrong number as the COG matches the compass. Deviation is 16 and Compass Offset (which was set by the system) was 2 degrees.

What is happening and how do I correct it?

[Chuck - Raymarine - Moderator]

George,

The maximum deviation sensed by the EV-1 CCU is too large. It is generally recommended that the maximum sensed deviation not exceed 9 degrees. Accordingly, it is recommended that the area around the EV-1/EV-2 CCU be inspected for magnetic field producing objects. No such object should be located within 3' of the EV-1 CCU. Please click here to view a FAQ addressing this subject. Should any source responsible for producing this deviation not be able to be relocated, then an alternate suitable source for the EV-1 CCU should be identified and the EV-1 CCU should then be installed in that location. After doing so, the Restart Compass command (MENU->SET-UP->AUTOPILOT CALIBRATION->COMMISSIONING->RESTART COMPASS) should be executed.

[George Bailey]

Chuck

I found and removed a magnetic source. Everything is working much better. Thank you. Deviation is now 2 degrees.

However, I’m still seeing a 2 to 15 degree difference or more between Heading and COG, with no apparent pattern to the difference and it’s not explainable by current or leeway (i.e., sometimes it’s in the opposite direction of what current or leeway would explain).

What should I try now?

[Chuck - Raymarine - Moderator]

George,

Should you not have already done so, it is recommended that you update the software within the Evolution autopilot's components with the latest available Raymarine product software updates. Should the software within the Evolution autopilot's components have been updated any time during the history of ownership, then it is recommended that the actions specified within the FAQ found here undertaken. Should the action above and those of the referenced FAQ have been taken, should the maximum sensed deviation be less than 9 degrees, and should the large difference between heading and COG persist, then please respond with a diagram of the system (hand drawn will suffice) identifying each of the marine electronics devices within the system and how they have been interfaced to one another. Should no issue be found with the installation, then it would be recommended that the EV-1 CCU be sent to Raymarine’s Product Repair Center to be bench checked / serviced.

[George Bailey]

Chuck

Based on comments on the forum, I changed the Speed Input to SOG. That significantly improved the performance. Any downside to using that setting? Otherwise I intend to leave it there.

Thanks.

[Chuck - Raymarine - Moderator]

George,

Within a system featuring a properly functioning and calibrated speed through water (STW) sensor (configure the system to display Speed and SOG ... these should be very close in value in the absences of leeway forces), STW will typically permit the greatest level of autopilot performance ... particularly in seas or when experiencing leeway forces (current and wind). However, should STW sensor not be functioning properly and/or not be properly calibrated and should STW be selected as the speed source for the Evolution autopilot, then the autopilot's performance will typically be adversely affected.