Adjusting Ritchie Compass to Chartplotter

RWS

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My chartplotter and compass are close, but i'd prefer they be CLOSER

Preferably DEAD ON !

I've been told I need to first confirm the DEVIATION has been set properly in my chartplotter for location & date

Then ...... I need to set the compass to the chartplotter

I have this compass adjustment book (attached) but am seeking an easier path

Any suggestions ?

RWS
 

Attachments

  • compass adjustment book.pdf
    1.9 MB · Views: 1
You cannot "set" "deviation" in a compass. You can adjust for deviation, but you will never zero it out due to hysteresis. Believe me, I've swung enough compasses to know. Think of deviation as "deviates". Little "deviates" who are trying to throw your compass off. Worse is they come and they go. Little things like your nav lights on, your refrigerator compressor running all have an effect. You will swing your compass to your most common running configuration, using the compensating magnets. You will basically be "splitting the difference" because if you zero out on one heading, you will have doubled your problems on the 90 degree to that heading. You split the difference on compasses with two compensating magnets, 1/4 them on high end units with 4. Then you place a deviation card on the compass that looks like this.

 
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While you can set your chartplotter/GPS to compensate for variation (the difference between magnetic north [your compass] and true north [your chart]), deviation is unique to your boat, and worse, like GeeBee says, changes w/ course. It's calculated by placing the vessel (or aircraft - they have the same issue) on a fixed compass rose and the vessel is physically 'swung' around the entire 360 deg. circle, taking readings at known points. Those points can be graphed, and used to correct a "desired course" to "course to steer." See GeeBee's attachment.
 
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