Compass Adjustment and Deviation Card

 A recent cruise in unfamiliar waters has reminded me of the need to calibrate Windstar's various heading indicators.  The Raymarine EV-1 heading sensor was way out of whack, and I had never checked Windstar’s factory-installed Ritchie Explorer binnacle compass. 

(issues with the Raymarine EV-1 heading sensor firmware are discussed elsewhere.)

Last weekend I noted COG, and magnetic compass headings for the EV-1 and the ‘ship’s compass’ on each heading at 10 deg increments.  The data is not as accurate as it could be for a variety of reasons, and I will repeat the exercise, focusing on ensuring smooth avg COG data, in 10deg increments as the baseline.   

Nonetheless, below is a suspicion-confirming plot of the recorded deviation values.   The centre represents -40 deg deviation, the outer ring +40deg, the extremes of the EV-1 deviation values.   Clearly the EV-1 firmware had issues, which were then corrected with the firmware upgrade.  The average deviation for the EV-1 is now 1deg, with maximum values in single digits.     The same is not true of the long neglected Ritchie compass, which clearly needs some attention.

 

This next chart is clearer, with a centre at -10deg and an outer boundary at +25.  (This visually overstates the negative values)  Whatever the data or presentation  flaws, the Ritchie is due for some attention. 

 I have not yet made any global adjustment to the EV-1 (this is an option in the software) and will do so after repeating this process to improve the data quality.  As noted above the average error only +1 deg, so this will likely be fine tuning indeed.

The Final image shows the the EV1 only, with the axis scaled to a sensible +/- 10 deg.  .  The single-digit deviation noted is mostly within the margin of error of my hasty data collection.  I expect it will improve and smooth slightly with more attention paid to the data, and also expect a that a minor compensation adjustment will reduce deviation further.