Is a magnetic compass at helm too old-school?

[peaman]

Today, I purchased a chart plotter to be mounted at the helm. It's a fairly modest unit manufactured under a label widely recognized as one which leans toward sailing versus motor yachts or fishing vessels. I unwrapped the unit and held it about where I had intended to mount it and I was stunned to see my primary magnetic compass rotate about 35 degrees. With a bit of testing, the unit seems to influence the compass when it comes within about 12" or so. I could find no mention of recommended distance from magnetic compasses in the included installation manual, so I visited the web page for "technical support". In the search bar, I entered (for example...) "zeus 7 distance from magnetic compass". Returns included guidance on installation of a fluxgate compass, adjustment of compass readings by the product, etc, but nothing about interference with an actual non-electronic magnetic compass. I'm from a place where a magnetic compass is a primary instrument which should be reliable even when all other instruments and systems fail, so I am disappointed and more than just a little surprised.

I have two fluxgate compasses on board, both of which provide NMEA 0183 data and which are well removed from the helm, but I'm having a hard time imagining giving up the traditional compass at the helm in order to avoid mounting the new chart plotter at an aesthetically ridiculous altitude above the helm.

What to do?

 

[Christian Williams]

Alas, my Ritchie Globemaster is a decoration.

With more than five GPS units on board (as many of us have) I hardly look at it. It never agrees with GPS anyhow.

And If GPS satellites went off line for any reason--all commerce depends on them--it would mean global war. Then I'd get out the chart and plot a compass course to, well, any port on the winning side.

 

[Bolo]

At the helm of my E32-3 I have an old Garmin GPS 540 and squeezed into one of the old "pods" (where the speed through water use to be.) a control/display for a Raymarine auto-helm. When I first purchased the old GPS 540 (before having the Raymarine) I noticed during installing it that when I got close to the the Ritchie Globemaster the compass would deviate up to 20 degrees or more. Looking in the instruction manual it stated that the GPS 540 should not be within 3 FEET of a compass. Yeah, well that wasn't going to happen. So I started to figure out why the compass would deviate when the GPS was held close by, with the power off by the way. I found that there was a magnet that kept a small door (see the photo) just below the buttons closed. Behind that door was a slot to insert navigation chips even though there was already charts installed in the unit. So, taking a big breath knowing that I was going to void the warranty.....probably, I removed the magnet from the inside of the door and the deviation went away. I find it strange that some GPS units are recommended to be installed away from a compass since the information you need from them is needed at the helm. I still use the 540, the readout on the Raymarine unit AND the compass. I find the compass easier to read when I want to follow a certain bearing. I guess is like the difference between digital and analog clocks. Last time I was at my doctor's office they gave me a cognitive test since I'm 70. The nurse gave me a paper and told me to draw a clock with the time of 10:10. I asked, "Digital or analog?" She didn't laugh probably cause she's heard that joke a hundred times before from old farts like me.

Anyway, my old Ritchie Globemaster will be going into the shop this winter to be re-built because it has a big air bubble in it. It'll cost about $300 but I think it's worth it.

 

[peaman]

I found that there was a magnet that kept a small door (see the photo) just below the buttons closed. Behind that door was a slot to insert navigation chips even though there was already charts installed in the unit. So, taking a big breath knowing that I was going to void the warranty.....probably, I removed the magnet from the inside of the door and the deviation went away.

This is fascinating. And sad.

Checking now to see if I can correct the chart plotter's GPS time based on my sextant's noon sights...

 

[peaman]

I found that there was a magnet that kept a small door closed.

I can see how that might happen from a poor design decision at some point, but crazily enough, it appears to be acceptable to the manufacturers.

Attached photos show my new chart plotter adjacent to my Wilcox Crittenden box compass of June, 1935 (it was good enough then....). The first picture shows the compass with the chart plotter several feet removed, the second shows the two adjacent with the left side of the CP next to the compass, and the third, with the CP on the opposite side. While the second photo shows very little change from the first, the third photo shows more than 60 degrees deviation. The deviation is caused largely (or wholly?) by a magnet built into the small door below the button panel, where chart chips can be inserted.

Of all the ways that such an interface can be designed to meet even the many environmental demands on such a thing, the use of a magnet on this type of device seems bizarre to me. At over $1300 for the unit, I will not be ripping the door off as you, Loren, so bravely did, but my opinion of this top-end vendor has been tarnished.

 

[Loren Beach]

Those little permanent magnet chip doors are dangerous. Our local marine electronics store people -- sales and technicians -- all despise them.
There are some chart plotters with friction catches on those doors, and after some depressing trial fits, we bought a Lowrance model with the friction catch. No problem with interference.
My surmise is that we are 1% of a market that is mainly fishing boats and power cruisers, and those boats have wide dash boards to mount stuff like this on. The warning is always buried fairly deep in the install manual, and refers to "compass safe distance".

 

[Filkee]

I still use mine. Not so much to steer a heading as to plot tacks.

 

[peaman]

I still use mine. Not so much to steer a heading as to plot tacks.

Before you tack, do you refer to a deviation table to make sure your tack to port is the correct angle from your tack to starboard? Just kidding, of course, but one problem with the magnets mentioned above is that the deviation is not some fixed amount. Instead, it varies, depending on your compass's heading. A few degrees off on a tack across the lake is likely to be no big deal, but when magnified to many tens of miles, it can make a significant difference. Or maybe I've just read too much of Bowditch.

 

[Frank Langer]

I like my Lowrance chart plotter alot, but still have my Ritchie compass as a backup, and won't do without it. Just like having paper charts on board as backup.
Frank

 

[Teranodon]

My 9" Gamin chartplotter, an older 78sc, and a VHF, are fairly close to the Ritchie compass, but I haven't noticed any really big discrepancy with the Raymarine electronic compass which is some 5 feet away. On the order of 10 degrees on some headings. So maybe Garmin has addressed this issue.

For me, the Ritchie has sentimental/aesthetic value only. I keep a hockey puck within reach. It's the little yellow item at 340degrees (oh no!). I use it frequently, leaning away from the pedestal.

 

[Filkee]

Before you tack, do you refer to a deviation table to make sure your tack to port is the correct angle from your tack to starboard? Just kidding, of course, but one problem with the magnets mentioned above is that the deviation is not some fixed amount. Instead, it varies, depending on your compass's heading. A few degrees off on a tack across the lake is likely to be no big deal, but when magnified to many tens of miles, it can make a significant difference. Or maybe I've just read too much of Bowditch.

“Plot” is probably too elegant a term for the way is use it.

 

[nquigley]

This is fascinating. And sad.

Checking now to see if I can correct the chart plotter's GPS time based on my sextant's noon sights...

I'm awaiting the results of your research with bated breath - Zeus is the plotter I've been planning to get too. And, I also want to mount it on a bracket above the compass.
If you can't find/remove a offending magnet in the Zeus unit, ... (warning - dumb magnetism question coming) ... can another magnet of similar size be affixed outside the case, in opposite polarity orientation, to neutralize the field generated by the original magnet, thereby eliminating/minimizing the compass deviation?

 

[Loren Beach]

can another magnet of similar size be affixed outside the case, in opposite polarity orientation, to neutralize the field generated by the original magnet, thereby eliminating/minimizing the compass deviation?

From what I know of watching a compass adjuster correcting out the error in ours and discussing what he was doing, the answer is 'no'. Adding more sources of error compounds the problem.

Easiest way picture the problem is to imagine a sphere of diminishing magnetic interference radiating out from the little (but quite powerful) permanent magnet in the chip closure plastic door on your plotter. The radius will be the "compass safe distance" specified by the manufacturer. Typical, from what reading I have done is around 19 inches - and some are much further.

Note the even without that magnet there will be some interference from the circuitry itself, altho this seems to be negligible beyond a few inches in the real world. Note B: the engineers that designed the plotter or any other device meant for helm location have done EXTENSIVE testing in a lab and their duty was to find the absolute minimum distance that will protect the company from the unpleasant PR of wrongful death lawsuits.

And then there is the compass. As the card tilts in all directions, the potential interference will vary some. You might as we'll imagine another sphere of 'protected space' around the card on your compass. When you park you handheld VHF in the cupholder in front of the guard you will notice the card moving some.... that's caused by the speaker in the radio. Often the same for any steel tool that you park there. And the drinking cup stamped out of mildly magnetic low-grade SS ? Probably.

If you love the plotter model too much to change it, just remember to remove it to the inside of the cabin when someday it dies (or the boat develops sudden electrical problems) and you are back to Plan B and plotting your course with chart, pencil, and dividers.

I have run into an employee at the local WM who was selling electronics (and he had a little badge proclaiming his training in that field) who said he did not know about magnetic interference and was glad to hear about this phenomena from me. Grossly Patronizing, yes, but ignorant too.
(We have a top notch bricks-n-morter marine electronics store close to my moorage and I am thankful for this bit of luck.)

 

[Jerry VB]

With a bit of testing, the unit seems to influence the compass when it comes within about 12" or so. I could find no mention of recommended distance from magnetic compasses in the included installation manual, so I visited the web page for "technical support". In the search bar, I entered (for example...) "zeus 7 distance from magnetic compass". Returns included guidance on installation of a fluxgate compass, adjustment of compass readings by the product, etc, but nothing about interference with an actual non-electronic magnetic compass. I'm from a place where a magnetic compass is a primary instrument which should be reliable even when all other instruments and systems fail, so I am disappointed and more than just a little surprised.

In the Zeus3 Installation Manual Section 8 Technical specification (p. 50) is the table entry:
| Compass Safe Distance | 50 cm |

:-(

On our boat, the fluxgate (electronic) compass is mounted in the settee by the mast (centered and low in the boat, just like the manual says).

On our first "sailing adventure", without thinking about it I loaded our food supplies into that bin because it was convenient. Our supplies included some "tin" cans. Oops! on our chart plotter, our boat was indicating it was crabbing through the water at about a 25 degree angle. :-O I moved the supplies and restored sanity.

 

[Christian Williams]

As I was leaving the dock for Hawaii I noticed that the whisky compass was 45 degrees wrong.

Yeah. Decision time. No actual compass for 6,000 miles? How smart would that be?

I pondered for five minutes, quite in a quandary . Of all the last-minute issues to pop up.

Meantime I was being shaded by my cockpit umbrella. Which I recalled, eventually, has a steel connection right next to the compass.

Whew.

Removed the umbrella, compass swung back to correct.

 

[toddster]

Under nominal conditions, my bulkhead compass and the fluxgate compass agree pretty well. As currently set up, I can see one while sitting on the port side and the other on the starboard side. I have to admit that I got a little paranoid while heading out the Columbia River Bar in misty conditions, and whenever I was out of sight of a buoy, kept my eyes pretty much glued on the compass.

Having a pretty small boat, I've discovered it's pretty difficult to keep the fluxgate compass free from interference. Sometimes, it's just something laying on the chart table (which is supposed to be far enough away...). Most recently, it was (I think) loading 150 feet of chain into the anchor locker. The area around the magnetic compass is safer from stored junk. Although come to think of it, the shelves I just added might intrude into The Zone.

There are iPhone apps that let you measure magnetic fields in places around your boat, using the phones sensors. "Gemeco iNstall" for one (by the parent company of Airmar transducers) "physics toolkit" for another. But also the hand-bearing compass works just as well to sniff out problems.
Yet another indication: There is a mile-long steel bridge that lands right next to my marina entrance. If I flip on the radar at the dock, any problem with the compass shows up as a distinct angle between the plotted image and the radar overlay. Of course, that just tells me that there's a problem, not where it's at.

 

[nquigley]

From what I know of watching a compass adjuster correcting out the error in ours and discussing what he was doing, the answer is 'no'. Adding more sources of error compounds the problem.

Easiest way picture the problem is to imagine a sphere of diminishing magnetic interference radiating out from the little (but quite powerful) permanent magnet in the chip closure plastic door on your plotter. The radius will be the "compass safe distance" specified by the manufacturer. Typical, from what reading I have done is around 19 inches - and some are much further.

Note the even without that magnet there will be some interference from the circuitry itself, altho this seems to be negligible beyond a few inches in the real world. Note B: the engineers that designed the plotter or any other device meant for helm location have done EXTENSIVE testing in a lab and their duty was to find the absolute minimum distance that will protect the company from the unpleasant PR of wrongful death lawsuits.

And then there is the compass. As the card tilts in all directions, the potential interference will vary some. You might as we'll imagine another sphere of 'protected space' around the card on your compass. When you park you handheld VHF in the cupholder in front of the guard you will notice the card moving some.... that's caused by the speaker in the radio. Often the same for any steel tool that you park there. And the drinking cup stamped out of mildly magnetic low-grade SS ? Probably.

If you love the plotter model too much to change it, just remember to remove it to the inside of the cabin when someday it dies (or the boat develops sudden electrical problems) and you are back to Plan B and plotting your course with chart, pencil, and dividers.

I have run into an employee at the local WM who was selling electronics (and he had a little badge proclaiming his training in that field) who said he did not know about magnetic interference and was glad to hear about this phenomena from me. Grossly Patronizing, yes, but ignorant too.
(We have a top notch bricks-n-morter marine electronics store close to my moorage and I am thankful for this bit of luck.)

Thanks, Loren - great comment.
I guess, the big picture is ... one would use/need the compass mainly when well off shore, and you want to follow a certain compass bearing for a loooong time - days, sometimes (the plotter would be used for AIS and radar inputs out there and not much else?).
But, when close to shore - usually by day, I'd guess - one would be glued to the electronic plotter, zooming in and out to get the needed detail for safe pilotage, and not relying on the compass hardly at all.
So, a hybrid setup might be to unplug the plotter from its pride-of-place location on the top of the ss frame that brackets the compass binnacle, and plug it into an alternative point on the boat's network (at the chart table?) when making an offshore passage, but to have it mounted on the ss frame the rest of the time, and ignore the compass card below it.

 

[Sailingfun]

I have an electronic compass unit as separate unit. One time I calibrated, it's enough reliable. If I lost 12v... Welll... There are a couple magnetic compass around...

 

[Christian Williams]

Let me add to or clarify my "obsolete" remarks.

Offshore, if the crew is steering (as when racing) I think nothing beats a big red-lighted compass, especially on a gray day or night with no cloud or star to aim for.

But few cruising crews steer nowadays, given the availability of various types of autopilots. Steering does give the night watch something to do, but I think most family cruisers would rather cut the watch to one and let folks sleep.

I have a small kayak compass below to keep an eye on the heading dictated by the vane or the GPS wheel pilot.

 

[Loren Beach]

I guess, the big picture is ... one would use/need the compass mainly when well off shore, and you want to follow a certain compass bearing for a loooong time - days, sometimes (the plotter would be used for AIS and radar inputs out there and not much else?).
But, when close to shore - usually by day, I'd guess - one would be glued to the electronic plotter, zooming in and out to get the needed detail for safe pilotage, and not relying on the compass hardly at all.

Reasonable conclusion.

Last time I really used our compass, though, was very near shore. I spend an hour or so in significant head seas crossing the Columbia River bar. (I should have waited another hour before heading out, for the ebb current to end, which is well after the slack).
With the boat moving "up 5, down 4, left 5, and left 4, and rinse and repeat" The damped compass was much steadier to watch than the indicator on the screen on our plotter.
I blame latency -- it takes fractions of seconds for the fast motions of the boat to be reflected in satellite reception time -- those satellites are a long ways away and then there is processor time to factor in also.
No complaints about either system, just a note that they each have their strong points.