Zeroing-in compass

Yachter Yat · February 07, 2018, 04:27:22 PM

A year, or so, ago I had to replace my Ritchie compass. Long story short, I ran with it all season last year without bothering to check its accuracy. Call it laziness on my part, I suppose, but I never bothered to check to see how close to true that thing was reading. This spring I'm going to attempt to get it "in line" with my GPS. I don't know what others have done, but I'm thinking of simply picking a nice calm morning on the water to try and run and adjust to my GPS.

I thought I'd simply run while staring at the compass on "0" degrees for a bit, then check against the GPS reading. I'd then make an adjustment and turn 180 to check at that heading. I realize it'll take more than one adjustment to get it right. Understandably, I'll have to take my local variation into account as well. Additionally, I believe repeating the process at 90 and 270 degrees will be necessary.

That said, I was wondering, has anybody out there done it that way, or do you have any input or pointers that might be helpful? Thanks.

Yat

Markshoreline · February 07, 2018, 05:55:29 PM

Start by applying a magnetic shield around your starboard wiper motor.

ATGEP · February 07, 2018, 06:36:28 PM

Mag compasses are always a compromise. There will usually be severl headings that are closer than others. When you dial in one heading, others will change. Best bet is to check n,s,e,w. See how far off you are. make ajustments per mfg and re check. When you get to the good enough point, re-run all cardinal headings and record the deviation. That way if everything craps out you will know west is 270+/- whatever.

beancounter · February 08, 2018, 04:26:41 AM

Impossible to do moving on the water. Do it at home or go to a nearby small airport and line up with runway for an accurate reading where the boat is pointed. But these cheap compasses are only so good with all the interference nearby.

BruceL2_Fish · February 08, 2018, 05:43:24 AM

Mark, if you need to shield the Starboard wiper motor, wouldn't you do both?

Yachter Yat · February 08, 2018, 06:33:28 AM

Thanks for the responses, guys. Mark, I hear you about the wiper interference. My compass "might" be immune from this as I have it mounted on a homemade aluminum bracket, whereby it hangs slightly "out-from" and below the bottom of the dashboard; directly under the steering wheel. It's quite a distance from that motor.

ATGEP, I suspect you might be right about that "compromise".....(if I read you correctly) meaning, I probably won't get absolute accurate readings in all four quadrants. It'll be interesting to see how close I can get.

Bean, before mounting the compass, I might have done something like you suggested. What I did was, tape the compass to a small board, then I clamped another board to a table. That enabled me to slide the parallel boards together (with the compass on zero) and then turn 180. Amazingly, it was very close. Leads me to believe there may have been some corrections done at the factory. I'm not sure I quite understand why you don't think it's possible to correct on the water?? Quite often, the conditions in Ipswich Bay are as flat and calm as can be....especially early in the morning. (What might help is, my rig seems to hold a steady course without even touching the wheel). Also, I'm thinking there's got to be at least "some" deviation being created, when running, that wouldn't appear when the boat is stopped and sitting still. To me, it seems things like the tach or sounder could have an effect on the adjustments. For that reason, I thought corrections under real operating conditions might be the way to go. We shall see, I guess.

Thanks again, Yat

straiteagle · February 08, 2018, 07:33:41 AM

You may already have this, but here is the information on installing and compensating a compass from the Ritchie internet site: https://ritchienavigation.com/media/336120/compensation-instructions.pdf

Markshoreline · February 08, 2018, 08:30:53 AM

Bruce, good idea to do both but the driver's side is closer to the compass than the other...

Yachter Yat · February 08, 2018, 08:41:54 AM

straigheagle; Yes I do have that, but thank you for posting it here. Good info for those who might be interested.

Yat

StreamFixer · February 08, 2018, 09:34:51 AM

Yat

Wiper motor has a magnet in it. Your compass will likely give you one reading regardless of direction pointed if that magnet is not shielded and the compass is within a couple of feet of the motor. Don't be concerned about deviation as you are adjusting to GPS bearing. That adjustment process will automatically correct for deviation.

My compass reads 30 degrees left. For some reason I cannot adjust that out. However, the card swings so much from wave action (up to 60 degree arc) precision really does not matter. It is sufficient to keep me going in the correct direction and I can do the 30 degree correction in my head...

As ATGEP implies, heading generally West will get you to a shore of some kind. That land mass is pretty hard to miss. Once you have found land you can figure out where you are (I hope) and navigate home accordingly.

We usually head just the opposite direction on the left coast :whistle:

StreamFixer

Yachter Yat · February 08, 2018, 10:12:26 AM

Fixer, thanks for that. You know, after Mark mentioned that wiper motor, curiosity got the best of me. I went out to measure the distant between the motor and the compass. Looks like approx. 15 1/2" between the two. I guess it's for that reason I was thinking it wouldn't be an issue. That said, now I'm really not sure.

I find it surprising you've got that 30 degree discrepancy. Seems almost impossible that could happen. Additionally, even more baffling that you can't adjust it out.

The other thing is the amount of "swing" your getting. I've never experienced that level of movement. Are you running a Ritchie? Mine is a gimbal mounted model; roughly 5" dia. with about a 4" face.

Yat

ATGEP · February 08, 2018, 10:25:07 AM

I flew more than my fair share of inflight swings on the p-3. We would adjust n/s the best we could on the ground and then fly gps headings and record the deviation using a card like this. For the wiper, you need to check it on and off as it may produce a bigger field when on. As long as you know what to steer, you are golden.

Yachter Yat · February 08, 2018, 12:22:51 PM

Atgep, thanks. Great idea and good to know. If push comes to shove, and I can't get that compass close, I'll definitely consider making one of those. Luckily, I never (or almost never) use my wiper. As long as I've owned this boat, I can only remember having to turn it on a few times. We try to avoid bad weather as much as possible, but........you never know.

Yat

metalwrkr · February 09, 2018, 09:21:38 AM

It is amazing to sit in your boat on your trailer and view your rock steady compass. Turn your wiper on and watch the card spin. If you have a lot of electronics on board, it is a good idea to turn each item on then off to see if it effects the compass. If you can't move an offending piece of equipment to reduce interference, you may have to post a cheat sheet as posted earlier. Remember, when proving out your compass and developing cheat sheets, you want to be on the water and not on your steel trailer. Also, check your local "Notices to Mariners" on your chart to make sure that there are no "Local Magnetic Anomalies" in the area you are using. RK

BurnsieBabe · February 10, 2018, 03:32:17 AM

At Arima we stoped putting a compass in the boat due to the wiper motor's interference. Back when we used the "anemic" wiper motors, there was no issue with the compass but lots of complaints about the weak wiper action. We did not realize, for about the a half year, that the newer stronger motors were making the compass almost useless, and quite possibly dangerous to rely on. I spent time studying the effect at different distances and with a single wiper vs one on each side. We were unable to come up with a generic mounting plan for all models, nor could we do it by model, due to the second wiper option.
Good luck to anyone planning to mount a compass.

Belinda

Yachter Yat · February 10, 2018, 06:11:29 AM

Hi Belinda; Thanks for the info. I have one off those "anemic" wipers. (ha) I actually like it..........for two reasons: First, it's small, so (to me, at least) it doesn't obstruct the windshield view quite as much as the newer pantographic models appear to do. Secondly, I could probably count the number of times I've used it on one hand.......and still have fingers left over. (haha)

That aside, after reading your post, I went out and tried turning mine on to see if I could detect any movement on the compass when it was running. Guess what?............It doesn't work!

Oh well.......At least I don't have to worry about that thing affecting my compass anymore.

Suppose I'll take a look when it warms-up.

I was thinking, the weather conditions encountered in the Northwest might be such that those wipers must be an absolute necessity. However, the way we pick our days here in New England, I can probably do without it. That said, if I ever bought a new Arima (such as described below :whistle:), I'd probably skip the wiper and just get one of those "clip-on" models that can be quickly mounted to the top of the windshield frame; in case of emergency.

Thanks again and don't forget........have fun!

Yat

BruceL2_Fish · February 10, 2018, 08:46:06 AM

I wonder is shielding like Mark suggests would make a difference?

Yachter Yat · February 10, 2018, 09:51:49 AM

Good question, Bruce. Additionally, I'd like to know what to use for shielding. Some kind of metal?

Yat

StreamFixer · February 10, 2018, 02:39:06 PM

There is a shielding 'foil' (actually thin sheet metal) that will help considerably. Won't cure it all, but really helps. With the newer motors, the magnets affect the compass whether it is on or not,,, just more so when wipers are running.

StreamFixer

Old No7 · February 11, 2018, 05:04:03 PM

Need an accurate compass heading?

I get ZERO interference from this wiper -- and the motor never burns out!

Old No7

StreamFixer · February 11, 2018, 05:25:38 PM

If you are not having problems, you probably aren't doing it "right"

StreamFixer

Markshoreline · February 11, 2018, 06:57:12 PM

Bruce, you have the advantage of a tall skip top. You could find an overhead mount compass such as this one https://www.amazon.com/Ritchie-Bracket-Mount-Sport-Compass/dp/B008YX4USI#customerReviews

You'd be able to get it about three feet from the wiper motors.

Yachter Yat · February 12, 2018, 06:04:10 AM

No. 7; That's the way I'd go next time. Simply clip-it-on, during those very rare occasions, when needed. As I said, though....probably wouldn't do in the Northwest. This may or may not be related to the subject (insofar as interference in concerned), but I'd also skip the horn. Now I just have to get Arima to build one of my "dream boats".

Yat

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Zeroing-in compass