Compass and Wiring 1977 CD 28

[Pembquist]

Working on the Electrical of my new boat I was struck by the location of the battery selector switch. It is very close to the compass as you can see from the attached photos. Judging by an old caution plate telling you not to switch off the battery while the engine is running I am assuming that this is approximately where the battery disconnect was located when the boat was built. I tried looking at the compass while fiddling with the switch and cabin light loads on and I can't tell if it causes any deflection when on vs off. In your opinions should I move the switch over to port so the wires are further away from the compass or is it not worth the effort?

[Neil Gordon]

Take the boat out and swing the compass, i.e., steer a series of courses on a calm, flat day, and compare your compass course with the indicated GPS course. (Watch out for current!) In each case, try this with the switch on and off and with all battery combinations. (Yes, you might need to turn the motor off!) Write it all down and you'll have a handy deviation table.

[CD_Sailor]

... I was struck by the location of the battery selector switch. It is very close to the compass as you can see from the attached photos. Judging by an old caution plate telling you not to switch off the battery while the engine is running I am assuming that this is approximately where the battery disconnect was located when the boat was built ... should I move the switch over to port so the wires are further away from the compass or is it not worth the effort?

A few (possibly incorrect) observations on this one.

First, the battery switch quite likely was placed where it is by the builder. You don't say when this boat was built, but the 28 had several variations in the interior liner and various equipments along the way, and I suspect the switch location was done at the factory. Since these boats did not normally come with a compass fitted, it was installed later by either the boat dealer or another owner. That means that it's possible that due diligence was not applied.

More importantly, the current through the battery cables is DC. This normally means that it will have no (or at least very little) effect on the compass magnets. Only a reversing or alternating current can do this.

Try Neil's advice (which you should should do in any case), and set up the compass correctly. There are simple ways to do this, many involving a hand-bearing compass. Also if you have some sort of navigation electronics that report compass headings underway, compare that information to the magnetic compass and adjust as appropriate.

In sum, I don't think you will be moving those heavy wires. It's likely easier to fit a new magnetic compass if you feel the need.

[barfwinkle]

JMTCW, But my guess is that the battery switch did not come from the factory in that location. It certainly doesn't look like a factory job.

Do a bit of "exploring" around the distribution panel, perhaps pop it out, and see whats back there. I think you may find a fiberglass repair or some old battery cabling still in there.

BTW I know the early 28s (as well as other older models) didn't have all the fancier interior trim as later models, but the mounting of the switch just doesn't look "right".

JMTCW!

Fair Winds

[hilbert]

FWIW, this was the factory installation on my 76 CD28. The switch in your photo looks more modern.

[tartansailor]

Neil's right. Everyone should prepare a deviation table,
and you should get a perfect sine curve if done correctly.
This is for determining your course as well as resolving issues as above.
If you had a good Deviation table you would not have to worry about the location of that switch
Remember the ditty: TVMDC
True Virtue Makes Dull Company, Add Whiskey
Dick

[Sea Hunt Video]

Remember the ditty: TVMDC
True Virtue Makes Dull Company, Add Whiskey
Dick

Dick:

I learned it a little differently - True Virgins Make Dull Company. Add Whiskey.

[hilbert]

I tried looking at the compass while fiddling with the switch and cabin light loads on and I can't tell if it causes any deflection when on vs off. In your opinions should I move the switch over to port so the wires are further away from the compass or is it not worth the effort?

I would not expect the location of the battery selector switch to influence your compass. The cables usually runs up to the switch and then back down 180 degrees and any DC magnetic fields cancel each other out. My compass was similarly situated and I never noticed any deviation due to DC electrical currents.

The DC magnetic field follows the Right hand grip rule.

[tjr818]

... The cables usually runs up to the switch and then back down 180 degrees and any DC magnetic fields cancel each other out. My compass was similarly situated and I never noticed any deviation due to DC electrical currents.

The DC magnetic field follows the Right hand grip rule.
[/quote]


If I remember correctly, the wires to and from should be twisted together to totally cancel each other out.

[gates_cliff]

Remember the ditty: TVMDC
True Virtue Makes Dull Company, Add Whiskey
Dick

Dick:

I learned it a little differently - True Virgins Make Dull Company. Add Whiskey.

And the "Politically Correct" version:

TV Makes Dumb Children, Add Wisdom