Windgen and Magnetic Compass Interference

[Sailmonkey]

Well, I got the following response from Ritchie Compasses
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I asked our engineering department and was told:
As long as the cable has a tight twist, there should be no problem, a loose twist, or a very course twist (1turn/foot) could cause some heading errors. If there is a minimal field leak it won’t be a problem because the cable is running up the mast. That will align that magnetic field with the vertical component of the earth’s magnetic field (which influences the tip of the compass card) instead of the horizontal component (which influences direction).
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Makes sense to me about the alignment of the magnetic influence......besides, what does it matter if the tip of the card is a little off??? I'll be tipped over anyway

[Christian Van H]

It's obvious that you MUST mount the wind gen down low, and the compass up the mast near the lower shrouds. THAT should take care of any interference! Twisting the wires should work. Use a cordless drill to twist em' quick and easy. If this fails, make yourself a compass correction card like this:

5 knots: 2 deg West
10 knots: 4 deg West
15 knots: 6 deg West
and so on...

[Sailmonkey]

Originally Posted by Christian Van H

It's obvious that you MUST mount the wind gen down low, and the compass up the mast near the lower shrouds. THAT should take care of any interference! Twisting the wires should work. Use a cordless drill to twist em' quick and easy. If this fails, make yourself a compass correction card like this:

5 knots: 2 deg West
10 knots: 4 deg West
15 knots: 6 deg West
and so on...

I've done a few miles of homebrew twisted pair wire with the drill method........but I was wondering about your correction card?? Where's the colum for apparent wind

[daddle]

Originally Posted by Sailmonkey

I asked our engineering department and was told:
... there should be no problem...

There ya go. Is this the engineering department at the compass manufacturer? I assume not. The compass manufacturer's engineering department says to keep conductors, twisted or not, three feet away, or something like that. Pretty clear instruction, and a well known fact.

The compass is very sensitive. From what I assume the wires will be very close to the compass, inches. Twisting certainly attenuates the field, but how much? By 1/2000? Doubt it. That's the difference between 3 inches and 3 feet says some poster above. And that ''not aligned' bit. A vertical wire is exactly what you would use to most confuse a compass.

Consider the dark stormy (windy!) night on a heading you didn't test....etc...

I wouldn't even bother testing it. It's hopeless. But what do I know?

[Sailmonkey]

Of course after I typed this I had an Epiphany. Daddle is the same one who is giving away all his paper charts since he beleives they're dangerous...........I have taken my grain of salt.

Originally Posted by daddle

There ya go. Is this the engineering department at the compass manufacturer? I assume not. The compass manufacturer's engineering department says to keep conductors, twisted or not, three feet away, or something like that. Pretty clear instruction, and a well known fact.

Try again......In the post I identified the source of the information as Ritchie compasses.

Originally Posted by daddle

The compass is very sensitive. From what I assume the wires will be very close to the compass, inches. Twisting certainly attenuates the field, but how much? By 1/2000? Doubt it. That's the difference between 3 inches and 3 feet says some poster above. And that ''not aligned' bit. A vertical wire is exactly what you would use to most confuse a compass.

Consider the dark stormy (windy!) night on a heading you didn't test....etc...

I wouldn't even bother testing it. It's hopeless. But what do I know?

Unless you yourself have tried it....I don't know what you know. I will try it, and compare to several known headings since I don't know and the manufacturer of the compass has told me I have a chance.
Hell, you want to get to the root of the thing, the mizzen sits on top of the engine that spins a 100amp alternator. Try and tell me that thing doesn't produce as strong of a mag field as the twisted wires from a small wind generator.

[daddle]

Dang...I didn't see that was from Ritchie. Nice! That's surprising that they think it's okay. Give it a tested try. I still doubt it will work when the wind generator is really cranking, but maybe it will. Depends how close the wire is.

As for the alternator...distance is everything. Cube-law. Plus the entire alternator design is meant to contain the magnetic field and make juice out of it.

[stark]

There is a material called "mu-metal". It is meant for shielding magnetic fields. You might get 5 to 10 dB of attenuation. Wrap it around the wire, not the compass -of course. And try to give it a couple extra feet above and below your compass.

In regards to what the compass engineer said, twisted pair is effective at canceling out the fields at far distances. But whats a "far distance"? Take the length of a twist, say its 1 inch... well if you are less than 1 inch from the twist, then the wires will hardly look twisted from your viewpoint, and the field will not be canceled out. However if your if your a foot or two, you'll have good cancellation.

My non-expert opinion would be to get a sheet of mu-metal and make sure your compass is the equivalent distance of at least 10 twists in your wire -I'd feel safer with 50 though.

The earths magnetic field is about 0.5 gauss. The wires on the wind-gen (assuming 12 Volts and about 200 Watts) will generate that same magnetic field at 4 inches (assuming not-twisted). But if you can get something like 10 twists/inch, at 4 inches away, you'll probably be fine.


Paul

[svaletheia]

If Ritchie says go for it, then go for it, but yeah, at least 2 turns/foot and I'd try for 3, depending on the gauge of wire you are running. If your compass is mounted like mine, you've got probably 4-6" of separation from inside the mast, so you might just be ok!

Good to go directly to the source like that, you occasionally get surprisingly good news from people who have done it before. Hopefully they aren't trying to sell you an accelerated compass re-magnetization package ;-)

[Christian Van H]

You might consider a small shield of unobtanium between the source and the compass. I hear it's REALLY expensive though...

[Sailmonkey]

Originally Posted by Christian Van H

You might consider a small shield of unobtanium between the source and the compass. I hear it's REALLY expensive though...

I could just run the wires through the mast and fill the lower section with lead shot, that should take care the magnetism. Plus if I ever need to shield myself from a Gamma emmiter I'll be covered

[Sailmonkey]

Originally Posted by svaletheia

If Ritchie says go for it, then go for it, but yeah, at least 2 turns/foot and I'd try for 3, depending on the gauge of wire you are running. If your compass is mounted like mine, you've got probably 4-6" of separation from inside the mast, so you might just be ok!

Good to go directly to the source like that, you occasionally get surprisingly good news from people who have done it before. Hopefully they aren't trying to sell you an accelerated compass re-magnetization package ;-)

Yep, same compass diving board. I may try it with the old el-cheapo compass first before I put the really good one on there.