Mounting a chart plotter and maintaining the recommended compass separation

[Wm. Gill]

I missed this in my original measurement, and planning. I am making a custom mounting platform for a GPS and control head for an autopilot. I have a Garmin UHD 64 and just noticed that Garmin recommends 25.6" spacing between the unit, and my compass. I don't know about other boats, but I can not imagine any way to install the GPS (chart plotter) at the helm and still meeting this spacing "requirement."
Does anyone have any thoughts or suggestions? I mean if the chart plotter is too far away, it's pretty much useless to these old eyes. In all honesty, I don't see the compass as much use without knowing where I am so that I know which direction where I want to go is.

 

[dmax]

Don't know about the UDH 64 but I have a Garmin 741XL mounted about 10 inches away from the compass - the compass works fine. Most sailboats have a similar set-up.

 

[jssailem]

It is hard to disregard the value of a compass on a boat.

Garmin is saying the UHD64 unit is producing a magnetic field which will affect a compass located with in 26inches. Perhaps you can test the engineering. Rig the UHD64 unit to work and try several locations. Then you can see the effects it has. If the compass turns towards the Garmin, when on, you know it is having an affect.

I found the motor on my AP was affecting my compass. So I altered the AP motor location and alll the tools arre now playing nicely together.

 

[Head Sail]

My Raymarine recommends similar spacing but I wanted the plotter and control head at the helm also. 15" of separation works fine with mine. Keep as much separation as practical and you should be fine.

 

[TomY]

I missed this in my original measurement, and planning. I am making a custom mounting platform for a GPS and control head for an autopilot. I have a Garmin UHD 64 and just noticed that Garmin recommends 25.6" spacing between the unit, and my compass. I don't know about other boats, but I can not imagine any way to install the GPS (chart plotter) at the helm and still meeting this spacing "requirement."
Does anyone have any thoughts or suggestions? I mean if the chart plotter is too far away, it's pretty much useless to these old eyes. In all honesty, I don't see the compass as much use without knowing where I am so that I know which direction where I want to go is.

I just installed a 5" Sitex plotter on a 24' motorboat and I gave it visual priority. There's very little space on a 'dash' forward of the wheel and the compass is mounted there.

Only option was to move it across to the other side. I nixed that immediately. I'm helping the owner (all new to him) get on the water. I want the plotter forward of the wheel, clear vision forward of the bow, right below his vision, easy to reach, at the helm.

I think of the CP as his 'minder', and we're working on getting him used to it. He'll often have young kids onboard which can be very distracting for the navigator at the helm.


I did test the plotter on and off and didn't see any movement in the compass, but that's not a total test.

I mentioned the potential for problems with the compass but told him you can always shut the plotter down if you start navigating on the chart book which I put on the boat. More importantly I've stressed redundancy of devices onboard(he gets that, GenXer).

We'll see how it works out. I'm most concerned with; moored boats and boat traffic in the harbor (clear view forward); and submerged hazards outside (his moving boat on the screen). Things happen really fast on a mobo. Also, I've first taught him about his wake and the damage it can do far out of his vision.

 

[dlochner]

There are free apps that measure magnetic fields. Look for GEMECO Marine Accessories.

With the unit on and off the strength of the magnetic field can be measured at varying distances. This will give an idea of how much, if any interference is present.

There are 2 sources of magnetic interference, the fields generated by the operation of the unit. These shouldn't be a problem when the unit is off. The second are magnetic latches for SD cards and covering access ports. These are on all the time.

Garmin has a long and respected history in avionics. Small compass errors at 500 mph are much more significant than at 5 knots. The engineers might or might not of recommended 26" spacing. What ever the engineers recommended no doubt the attorneys increased the distance.

 

[Wm. Gill]

Don't know about the UDH 64 but I have a Garmin 741XL mounted about 10 inches away from the compass - the compass works fine. Most sailboats have a similar set-up.

Just for grins I looked up what Garmin had to say about compass-safe distance on the 741XL and it's 17.7" Oddly, something I read is that Garmin uses a permanent magnet to keep the SD slot cover closed, and that not the operation is what messes with the compass. I will try to see what happens when the unit gets near the compass. Where and how I planned to mount the UHD 64 is about 12 to 15 inches away at best.

 

[FastOlson]

That permanent magnet chip door closure was one of the single most dangerous ideas to come down the Stupidity Freeeway. On almost all sailboats these instruments will get installed a few inches above the compass on the inside the ss grab bar loop.
There are some models from some makers that use a friction catch for those little 'doors' and we have one on our Lowrance 9" plotter. No interference at all. (when doing the install I tested two other models with the magnet and both would move the needle on the compass.)

Keep shopping, and complain to the instrument builders. Let them know that burying the safe compass distance warning on page 400 in small print in a pdf manual will not totally protect them from a jury of 12 average cynical persons............ And the stores/web sites that sell this stuff with zero warnings will likely get their turn in court as well.

 

[Ken Cross]

There are more than 2 parts to this. Distance from the compass is also dependant on which direction. My Garmin plotter is above the compass and really close. It doesn't seem to interfere. Power off is one thing, power on is another. for power, be sure to twist the power and ground wires around each other. This will help neutralize the effects of the DC current. Now power it up without mounting it and move it around the compass while watching the compass heading. If the movement isn't there, you should be good. Keep it in that position and power it down while watching the compass. No movement is good. Your compass should be less sensitive to a magnetic field from above or below.

 

[Wm. Gill]

There are more than 2 parts to this. Distance from the compass is also dependant on which direction. My Garmin plotter is above the compass and really close. It doesn't seem to interfere. Power off is one thing, power on is another. for power, be sure to twist the power and ground wires around each other. This will help neutralize the effects of the DC current. Now power it up without mounting it and move it around the compass while watching the compass heading. If the movement isn't there, you should be good. Keep it in that position and power it down while watching the compass. No movement is good. Your compass should be less sensitive to a magnetic field from above or below.

I am counting an that. The proposed spot for my plotter is almost directly above the front quarter of the compass, about 13" away, and any lines of magnetic force almost directly perpendicular to natural magnetic forces.

 

[Ken Cross]

Ours is about 6 inches away. I'm headed that way now so I'll take a picture.

 

[Ken Cross]

Here is a photo of ours. As you can see they are very close and the compass works just fine.

 

[FastOlson]

Note: having the plotter powered up or not has NO effect on the magnetic field from the powerful little perm. magnet on that chip door. Read the manufacturer's compass-safe distance minimum distance info again.
They employ engineers to design and test their devices and advise you to be safe, in spite of the glib salesperson at a chandler whose interest in your safety comes waaaaay after their efforts to get your VISA card to operate smoothly and safely guide your payment into their account.

 

[Wm. Gill]

I finally got to test the Garmin chart plotter's effect on the compass. I carefully studied all 4 points of the compass. Then I put the Garmin where it is to be mounted, and watched for any variance on the compass. There was none. I repeated this, positioning the Garmin at various points around the compass, but at the same relative angle and distance as if mounted. These alternate positions are unusable as mounting points, but it let me simulate the influence as if the boat had rotated 360 degrees. No detectable compass movement at any point. Then, as a final test, I put the Garmin on the same plane as the compass and got detectable movement at every point around the compass at the same distance between the 2. I am only about half the distance Garmin says is safe, but virtually over head of the compass. My theory is that the more the distance is perpendicular to the plane of the compass, the less the influence, and therefore the less the safe distance.
So I feel comfortable I don't have a problem. If real life contradicts me, I will be sure to let everyone know.

 

[capta]

I missed this in my original measurement, and planning. I am making a custom mounting platform for a GPS and control head for an autopilot. I have a Garmin UHD 64 and just noticed that Garmin recommends 25.6" spacing between the unit, and my compass. I don't know about other boats, but I can not imagine any way to install the GPS (chart plotter) at the helm and still meeting this spacing "requirement."
Does anyone have any thoughts or suggestions? I mean if the chart plotter is too far away, it's pretty much useless to these old eyes. In all honesty, I don't see the compass as much use without knowing where I am so that I know which direction where I want to go is.

Mount it anywhere you want to, then have it "swung" by a professional. Every one of us should have a fairly up to date deviation card aboard, anyway.

 

[Ken Cross]

Note: having the plotter powered up or not has NO effect on the magnetic field from the powerful little perm. magnet on that chip door. Read the manufacturer's compass-safe distance minimum distance info again.
They employ engineers to design and test their devices and advise you to be safe, in spite of the glib salesperson at a chandler whose interest in your safety comes waaaaay after their efforts to get your VISA card to operate smoothly and safely guide your payment into their account.

Actually, the power can have an even larger effect than the magnet depending on the location of the device. That's why I specified twisting the power and ground wires together. This is important. And yes I have dealt with this on a professional level throughout my career. Anyone can swing a compass, but to get the best results you must start with as good of a native system as you can get. The manufacturer's info is written in ideal lab conditions. We can't always get that ideal separation and still need to do the job.