Where did you mount your compass?

[James V]

There has been some debate on where or where not to put a compass. Where is the best place on a Mac?

[Beam's Reach]

Mine is on the starboard bulkhead, but I don't know if that's the best spot. That's just where it was when I bought the boat. I've often thought that the pedestal would be a better spot for the compass and the depth/wind/log since I can't see them very well on the bulkheads when other people are sitting in front of them.

[Chip Hindes]

Mine is on the portside bulkhead where it was mounted by the dealer, and that is the wrong place. I found that switching on the running lights changes the indicated heading by nearly 10 degrees. I never noticed this before I substantially upgraded the electrical panel, but I also never checked it. Some of the the wiring is a little closer to the compass than stock, but I can't believe it's enough closer to have created an effect where none existed before.

For the same reason, I'm pretty sure I don't want it anywhere near the pedestal. My pedestal is loaded up with electronics and lighting, and though I also haven't checked for magnetic "leakage" I'm guessing the autopilot motor which is no more than a foot away from the top of the pedestal is almost sure to throw off the compass.

My plan is to move it to the starboard bulkhead. The only wiring near there is the light in the head. That's off most of the time, but if I have to I'll move it further away or maybe switch to an LED light with much lower current consumption. What's preventing the move right now is comptemplating the big freaking hole it's going to leave in the portside bulkhead.

[Terry]

I have a nice hand held bearing compass but I mounted the holder for it on the starboard bulkhead where no other electronics can influence it. (works like a regular mounted one) Even if I hold it in my hand on the pedestal it is pulled off by 10 degrees or so, something there seems to influence it. The only drawback is that on a broad reach the mainsheet gets caught on it and pulls it out of the holder. Luckily it floats cause I had to fish for it once, now it is clipped via lanyard to the stantion so that it doesn't go overboard again on a broad reach.

[Jim Bunnell]

Like Terry, I use a hand held as a back-up (main compass is part of auto-pilot). I mounted its holder on top of the hatch; nothing electrical around at all, easy to see, out of the way and easy to grab if I need to take a bearing.

[Pouw Geuzebroek]

I found that switching on the running lights changes the indicated heading by nearly 10 degrees

Chip, I have it there too, but have not noticed the misplacement. When you did the upgrade did you bared in mind that the wires of the compass light should be coiled towards the electical panel? I have read somewhere they should be coiled to prevend interfearence with the compass.

[Robert]

I found that spot was great except once when powering ahead of a storm in very rough seas that forced me to drive without my glasses. I could barely read it between salt water slaps in the face. I would have liked the compass a little closer in those conditions.

[Chip Hindes]

I have read somewhere they should be coiled to prevend interfearence with the compass.

When I did the upgrade I didn't do anything to the compass light wires. I suppose I should check them anyway. If that were the problem, it would certainly be easier than moving the compass. I could easily disconnect the compass light from the rest of the lighting circuit and see if the problem is still there.

Twisting paired wires is a common method of reducing interference from magnetic fields, but the wires must be separated at teminations, switches, etcetera, and there's a lot of that going on in behind my DC panel.

[DLT]

Keep in mind that twising wires is a common method of reducing both received interference and generated interference.

I'd submit that the compass light is not impacted greatly by received interference. Rather, it is more likely a significant source of interference.

I'd bet that where those wires enter the compass housing itself, they are rather close together. They are almost certainly routed and otherwise arrainged internally to minimize interference. At any rate, all you can change is how they are routed outside the compass housing. I'd twist the hull out of them.

Also, strength of a field is directly proportional to current, but diminishes greatly with distance. I can't remember but it is either by a factor of the distance squared or cubed. In either case, where those wires terminate to the panel, they are almost certinly less troublesome that other higher current carrying wires to the panel.

So, what you really want to do is to twist all wires going anywhere near the compass, especially the higher current wires...

[Jack O'Brien]

My used X came with a small Richie compass mounted top center on the pedestal and the fluxgate compass for the SportPilot mounted low, inside the pedestal right next to all the wires and cables running through the pipe in the floor. I moved the fluxgate to the aft head wall as low and toward center as possible. No wires or metal there.

The Richie compass is on a shelf in my garage as it is only suitable for mounting on a horizontal surface and I have too much electrical stuff on a "dashboard" on the pedestal. I mounted a big, new compass on the starboard bulkhead. No wires behind it.

The boat came with a Garmin GPS mounted on the port bulkhead. I would like, someday, to have it, or a new color GPS, on a swing mount on the pedestal. Then I'll use the hole it leaves as a "glovebox".

[Chip Hindes]

So, what you really want to do is to twist all wires going anywhere near the compass, especially the higher current wires...

The circuit causing the problem with my compass is the lighting circuit. I know this because I can reach inside while watching the compass, flip the running light switch on and off, and watch the change.

Besides the lighting circuits, the only "high" current wires I'm running through the panel at this time are the bilge and water pumps. I have three bilge pumps wired through a single on-off switch, normally off, no float switch. The water pump is a demand type and it's only on for a few seconds when the faucet is opened. In any case, they're off 99.9 percent of the time when underway and in the vanishingly rare event I'd need to do so, I can shut them off to take a compass reading.

Power to the radio, pedestal, stereo and DC to AC inverter are on separate, fused circuits which are not routed through the power panel.

I will check the wires to make sure everything that can be twisted is twisted, before ripping out the compass.

I don't mean to hijack this thread with my own particular problems, but I must add that the fluxgate compass for my autopilot was also affected by a stereo speaker mounted about 15" away. It was the only reasonable place to put the fluxgate, I figured it was going to be too close when I mounted it, but the speaker was already there and I figured what the heck, maybe I'll luck out.

Not. On swinging the compass, I had over 50 degrees correction. Moved the speaker about four feet away (better location acoustically, anyway) and the compass swung a two degree correction. And a large hole to cover.

[DLT]

Chip,

I have no doubt that you are right in that your compass lighting circuit is the culprit. Twisting those wires, if they are not already will surely give you some improvement.

If they are already twisted, or that doesn't help enough, try wrapping them in some foil. Obviously, you don't want the foil to contact both the positive and negative contacts, but you should be fine having it contact the negative, thereby grounding the foil. That should kill a lot of the interference from the lighting wires...

Also, it goes without saying that you don't want to sheild the compass itself...

[RandyMoon]

Mine came on the port bulkhead. I would have preferred it closer to the pedestal because it is hard to see the actual angle of heel.

Solution, my GPS is mounted on the pedestal and I can switch it from "map" mode to "compass" mode. Plus I have a stick-on Inclinometer
on the pedestal.

[Chip Hindes]

If they are already twisted, or that doesn't help enough, try wrapping them in some foil. Obviously, you don't want the foil to contact both the positive and negative contacts, but you should be fine having it contact the negative, thereby grounding the foil. That should kill a lot of the interference from the lighting wires...

I'm not an expert in this matter by any means but I'm almost certain that the magnetic field and ferrous materials that throw a compass off is fundamentally different from electromagnetic interference - EMI. Aluminum foil, lead, mu metal and the like, can shield from EMI, but have no effect on a magnetic field. Can somebody confirm, or better yet, explain it better than I? Words of few syllables, please.

Solution, my GPS is mounted on the pedestal and I can switch it from "map" mode to "compass" mode.

Not quite your total solution. I have the GPS compass, and a backup in the fluxgate compass for the autopilot, but the "manual" compass doesn't require power or satellite reception. Of course, if the others fail, you can probably figure out some way to read the manual.

[baldbaby2000]

Mine is on the pedestal. It seems to work fine but I have yet to do an accurate comparison with my GPS.

As I recall from my fields classes many years ago the magnetic dipole (no such thing as a magnetic monopole) field strength drops off as the cube of the distance. Electromagnetic fields such as transmitted by your marine radio antenna drop off as the square of the distance.

BB