? For those that have done calibrations on ritchie compasses with comp rods

[KC8QVO]

How accurate are/were you in dialing in the headings with the rods? What did you use for a reference? I have a small Ritchie X-10-M. I calibrated it before and it seemed like it was OK. I set it up on a different boat and didn't have a good way to verify calibration so I left it from before. I think northerly headings were fine but southerly headings were east of what they should have been. What has been your experience? What challenges have you run in to and how did you correct for them? What did you use as a reference? When traveling long distances do you calibrate for declination or factor it in to your readings?

 

[KC8QVO]

Moderators - please delete. Dupe post.

 

[Ned L]

You are talking about correcting for deviation (the error imparted to the compass by localized ferrous and/or magnetic objects, …. Like within 5 feet or so.) This is nothing to do with compass variation which has to do the changes and anomalies in the earth’s magnetic field, and magnetic north being different than true north.
The process of correcting for deviation is known as "boxing the compass" . If you have corrected the compass on one boat, that effort and correction will be meaningless and worthless if you move the compass to another boat. Things that affect a compass and create error are speakers nearby (biggest issue due to the magnets in them), steel objects nearby, radios, even things as harmless seeming as soup cans stored in a cupboard in the cabin just below the compass. ANYTHING magnetic, steel, or containing magnets near a compass will cause deviation.
Normally you correct the compass as closely as is reasonable and then create a deviation table so that you know how many degrees deviation you must correct for from your compass reading to get to the actual magnetic heading.
When boxing the compass you typically take a separate compass aboard the boat that can be temporarily located somewhere where it will not be affected by any steel, magnetic objects, or magnets, and use that compass to compare to and correct to and create a deviation table from. Correcting a compass is a whole topic that careers have been made of.

Declination is the same as variation, and you very much need to correct for that when navigating and traveling distances. Traditional paper navigation charts always contain two superimposed compass roses so that you can see the local variation.

 

[KC8QVO]

If you are trying to calibrate off of another compass isn't the other compass just as susceptible to magnetic interference as the one you are calibrating? I see the point about locating the reference compass away from other objects, but Im still wondering how you verify the accuracy of it. As far as declination and true vs magnetic north - am I understanding you correctly that you use magnetic north and factor in the declination from the chart? The chart I have shows from 2000 and reads 1deg 57' E, then add 7' W per year after. So that would be 0deg 19' today. I suppose that is close enough to magnetic N the direct magnetic readings would be good enough.

 

[Ned L]

You don't correct a magnetic compass to read to 'true north'. Yes, you correct it to read to magnetic north and then correct to true north for navigation using the variation correction off the chart. (Yea, ..... I'm not sure I would want to use a 'corrected' variation off a 14 year old chart.)
In order to verify the compass you are using for boxing you would plot a course between two known points on a chart (and on land) and then run that bearing and check your compass heading against the plotted heading (this should be done on a variety of headings to check that your reference compass is ok). ---- As I said, there is a lot to this topic.


Correcting a compass is a process that can take hours out on the water, running all sorts of different directions, and a lot of trial and error with the correcting magnets to find the best happy medium. Rarely can all the deviation be taken out.

 

[KC8QVO]

I found a report from the local airport from 7/24/14 that shows magnetic variation is 2deg East. That is a ways off of 0deg 19min from the chart numbers so I see what you mean. Yea there is a lot to a compass. The hard part is knowing how accurate it is and being able to trust it with so much that can affect it. I will rarely ever be holding a course for more than a couple miles at a time though. There isn't that much open water on most of our lake unless I get to the big bay. My goal is to get accurate enough that I can pin the boat through the right channel from a buoy. Thats where I got goofed up before - hit a lot of bays and not the right channel, was always off to the south (reading too far east).

 

[Ned L]

Compasses are simple devices, but a lot of things can screw them up. They are an important tool and when understood, respected and treated properly is something that you can basically trust your life with. The deviation table is a critical piece of the equation for using a compass with confidence.

 

[Outsider]

You can use heading when swinging a compass, and with enough speed to maintain a steady heading. Look https://www.ritchienavigation.com/re.../compensation/

 

[Thalasso]

I found a report from the local airport from 7/24/14 that shows magnetic variation is 2deg East. That is a ways off of 0deg 19min from the chart numbers so I see what you mean. Yea there is a lot to a compass. The hard part is knowing how accurate it is and being able to trust it with so much that can affect it. I will rarely ever be holding a course for more than a couple miles at a time though. There isn't that much open water on most of our lake unless I get to the big bay. My goal is to get accurate enough that I can pin the boat through the right channel from a buoy. Thats where I got goofed up before - hit a lot of bays and not the right channel, was always off to the south (reading too far east).

[h=2]Magnetic Declination - Compass - how to use one[/h] www.[B]compass[/B]dude.com/compass-declination.shtml