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Old 02-04-2010, 06:49   #1
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Compass Correction

I started off with my boat's original 40 year old flush mounted compass. I stepped on it, coming down from the forward deck and broke the globe. It was yellow, old and brittle and scratched up, so no surprise, and no bother.

I replaced it with a decent Silva from the local chandlery. I observed that it really seems to be about 30 degrees off. Before I could start messing with the correction screws, one of my inexperienced buddies came down from the deck, stepping on it and broke the mounting ears.

I have purchased yet another compass, and just placing it in position for a test-fit it too, appears to be about the same 30 degrees off.

The only thing I can come up with is that I recently made a winch handle for my halyard winch out of 12" of 1/8" thick flat, steel stock. It is stowed in the winch handle pocket about 1' from the compass.

Is that amount of steel enough to drag the compass off that far, or do I have other problems?

What is the better fix- Calibrate the compass against a GPS or relocate the winch handle stowage? (I hate drilling new holes)
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Old 02-04-2010, 06:52   #2
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The winch handle could be the problem. A foot away is not far in magnetic terms. Hate to ask the obvious, but have you tried moving the handle to see what happens to the compass?
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Old 02-04-2010, 07:11   #3
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That test is today. It only dawned on me while I was here, at work.
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Old 02-04-2010, 07:14   #4
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Quote:
Originally Posted by BubbleHeadMd View Post
... What is the better fix- Calibrate the compass against a GPS or relocate the winch handle stowage? (I hate drilling new holes)
Replace the steel winch handle with an aluminum or plastic verswion, then swing the compass.
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Old 02-04-2010, 07:22   #5
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Move the winch handle? Considering the track record of damage, how about moving the compass? To a sheltered place?
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Old 02-04-2010, 07:31   #6
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Heh..yeah I know. Hey, the other one survived 40 years.

Gord: I have OLD winches that use flat metal bodies that slip into a slot on the top of the winch, not the common star-shape. I just realized that what I should have done was get aluminum stock instead of steel.
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Old 02-04-2010, 08:49   #7
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Rig-Rite has Aluminum (“Marinium”) winch handles for the old Wilcox-Crittenden sheet winches (Flat, Slide-in Winch Handle is 1 7/32" wide x 3/8" thick with spring locking mechanism, handle extends 2 1/2" into winch from underside stops).
They may also have the Merriman bottom action winch handles (Bronze, I think).
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Old 02-04-2010, 08:56   #8
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Hey thanks Gord!
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Old 02-04-2010, 12:55   #9
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Hey Bubblehead;
Check that the wiring to the compass light is a twisted pair. Another thing; have you installed a new stereo? Magnets.
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Old 02-04-2010, 14:37   #10
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You really should get it within about 15 degrees before starting the adjustments.

Quote:
Originally Posted by BubbleHeadMd View Post
That test is today. It only dawned on me while I was here, at work.
I'm sure there are instructions, but...
* try it with all your gadgets on and off
* make sure it is truly pointed straight ahead
* make a guard, if you like the location. not difficult, if you can make a winch handle. Use aluminum or brass ()
* adjust the compass at slack tide and with light wind
* if you are using gps, either get the declination from the chart or set the gps to magnetic

Amazing that Columbus ever got here.
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Old 02-04-2010, 16:40   #11
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With all the handheld and cockpit mounted GPS units, why have a compass mounted on the boat? The only thing it indicates is which way the bow is pointed.

Set the GPS to indicated a true bearing to match your charts and you don't need to dink around with devaition or veriation or what the heck direction the boat is really going(COG).
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