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Sailmonkey · 13-04-2010, 15:47

I'll shortly be installing a wind gen on the mizzen. That being said, the magnetic compass is also mounted on the mizzen in front of the helm. What I'm thinking about doing to avoid a magnetic field from the dc current is forming the 8awg wires into a twisted pair for the run in the mast in the vicinity of the compass (say 3' above and below).
Is this a logical thing to do? Has anyone else done such a thing with success? any other suggestions?

Sailmonkey · 13-04-2010, 19:20

16 lookers and not even a comment yet?

daddle · 13-04-2010, 19:32

'Cause you can't know withoout trying it. First guess is you are asking for compass trouble. Second is it will be very hard to test (high wind, all headings).

I pondered for a while what twisting does to the field at any one small place nearby, but couldn't imagine just what happens. In general, over a large area, it cancels out.

It's too bad if it doesn't work because that leaves only drying laundry as a practical use for that mizzen mast....

senormechanico · 13-04-2010, 19:48

If it actually has an effect, move the compass.
Otherwise fuggedaboudit.
And I'm not even from New York.

seandepagnier · 13-04-2010, 20:44

if you twist the power wires going to the wind generator, they will essentially cancel the field. It is unlikely it have a negative influence since you care about heading from the compass... if you were taking other measurements you might have issues.

Sailmonkey · 14-04-2010, 06:59

I'll assume that no-one else has tried something like this then. Moving the compass is not as practical as one might think, the bulkhead one isn't visible from the helm, and I have no binnacle.

Well, I'll just do it and worry about the unintended consequences as they make themselves known.

svaletheia · 14-04-2010, 07:10

Best thing to do is to locate another compass elsewhere ahead of time, calibrate it against the initial mount, and probably a GPS to be sure. Then when you try the installation, you can check deviation against a known quantity.

However, as one with a degree in electrical engineering, I can say with near certainty you are asking for trouble. Even twisted wires give off local fields and twisted wire that large (greater area of local field between twists) carrying that much current will DEFINITELY hose your compass, and I'm not talking about small deviations either - you run the risk of potentially demagnetizing or at the least desensitizing your compass needle. I would NOT do this personally, but its your boat... The thing is that the problem will most likely initially be either very subtle (e.g. gentle over time skewing of the compass needle) or situational (in which case you may or may not notice the transition until you notice the effects - e.g. going the wrong way) and will likely get worse over time rather than showing up all at once. The uncertainty alone is enough to make me concerned about something that important.

And why are you putting a windgen that high up anyway? That kind of additional wind load and weight on the extreme top of your mast - even a mizzen - doesn't seem like a terribly bright idea to me.

Sailmonkey · 14-04-2010, 07:17

Quote:

Originally Posted by svaletheia

And why are you putting a windgen that high up anyway? That kind of additional wind load and weight on the extreme top of your mast - even a mizzen - doesn't seem like a terribly bright idea to me.

Not on top, just above the lower shrouds. I do this as I have limited realestate for panels, and no way to pole mount since the mizzen boom hangs over the transom.

svaletheia · 14-04-2010, 07:27

Ahhhh, ok. I get it now. I have an idea for that, actually, since our boats are similar in that regard, but I'll take that offline. I assume you are choosing a smaller unit in order to fit there? I have a radar dome in about that location but its only 18" in diameter and I can't see putting something much larger in "swing radius" in that location without coming too close to the mainsail topping lift.

Either way, if you can make it work then that's good, but I would definitely make an attempt to relocate the compass - demagnetization is expensive to fix and leads to untrustworthy instruments. Another option for you, and I'm not sure how good this idea is but its an option, is to run the twisted pairs down one of the shrouds and/or run a dedicated guide wire for that purpose. That would keep them > 3 feet from the compass, at the risk of increased weather exposure. Its not an idea I recommend but if you insist on keeping the compass at the base of the mast and mounting a windgen on the same mast, its much better than some alternative consequences.

Sailmonkey · 14-04-2010, 07:51

Quote:

Originally Posted by svaletheia

Another option for you, and I'm not sure how good this idea is but its an option, is to run the twisted pairs down one of the shrouds and/or run a dedicated guide wire for that purpose. That would keep them > 3 feet from the compass, at the risk of increased weather exposure. Its not an idea I recommend but if you insist on keeping the compass at the base of the mast and mounting a windgen on the same mast, its much better than some alternative consequences.

I had thought about that too, but I can't stand the thought of running wires outside like that. Seems to me to be unfinished and just sort of slapped together.

daddle · 14-04-2010, 08:29

Run the wires next to the compass. It will be a wonderful thing to be able to look at the compass and see how much charging the wind generator is doing.

seandepagnier · 14-04-2010, 08:35

it really depends on how far the compass is from the wires (duh) but keep in mind that doubling the distance drops the effects by a factor of 8. The trouble with the wind generator is the current is always changing. Maybe you can stick the magnetometer on a pole 1-3ft from the mast.

Now it would be possible to completely compensate this in software if the magnetometer calibration has access to the wind generator current.

Why do you need the compass anyway? If its for an autopilot, then it might still work pretty well, and might even point higher (on one of the tacks) when wind increases which is actually a good thing!

Sailmonkey · 14-04-2010, 09:21

Quote:

Originally Posted by daddle

Run the wires next to the compass. It will be a wonderful thing to be able to look at the compass and see how much charging the wind generator is doing.

Seems a little expensive when a good inline ammeter is less than 0.1 boat units.......

Sailmonkey · 14-04-2010, 09:24

Quote:

Originally Posted by geckosenator

it really depends on how far the compass is from the wires (duh) but keep in mind that doubling the distance drops the effects by a factor of 8. The trouble with the wind generator is the current is always changing. Maybe you can stick the magnetometer on a pole 1-3ft from the mast.

just a plain old magnetic compass that would be really hard to see on a pole

Quote:

Originally Posted by geckosenator

Why do you need the compass anyway? If its for an autopilot, then it might still work pretty well, and might even point higher (on one of the tacks) when wind increases which is actually a good thing!

Ummmmm......I like to have a compass to steer by when navigating by sight. the autopilot can do it's own thing.....