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  #11  
Old 04-25-2009
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Good point.. I forgot that compass cards for the other hemisphere might also do this.
Quote:
Originally Posted by Omatako View Post
If your compass card has always been like this (i.e. you can't remember seeing it any other way) then the chances are the compass was manufactured for the other hemisphere.

The magnetic variation of the earth is such that as you proceed from far north to far south the compass card starts to lean. The compass manufacturer will glue a tiny weight onto the underside of the card to compensate for this and the compass will often display the lean tendency when going to the opposite hemisphere.

It sounds like you have a southern hemisphere compass in the northern hemisphere.

This is often evident in older compasses, I believe the later models don't do this.
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Old 04-25-2009
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Quote:
Originally Posted by sailingdog View Post
IIRC, not all compasses were filled with oil. You really should check to see what the manufacturer, if they're still in business, recommends.
I doubt they are (and if they are - I doubt they remember) - it's been 37+ years
Actually I am thinking of replacing it. The compass has 5 degree gradations and I'd like something a bit bigger and a bit more precise. May be at the end of the season though - I have my hands full with projects and the boat is nowhere near water yet.
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Old 04-25-2009
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Quote:
Originally Posted by Omatako View Post
If your compass card has always been like this (i.e. you can't remember seeing it any other way) then the chances are the compass was manufactured for the other hemisphere.

The magnetic variation of the earth is such that as you proceed from far north to far south the compass card starts to lean. The compass manufacturer will glue a tiny weight onto the underside of the card to compensate for this and the compass will often display the lean tendency when going to the opposite hemisphere.

It sounds like you have a southern hemisphere compass in the northern hemisphere.

This is often evident in older compasses, I believe the later models don't do this.
I guess as much. Think I'll just leave it as is since it still works. Thanks Andri.
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Old 04-26-2009
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Some compass makers offer very reasonable repair or replacement services, so first call the maker.

Compass fluid varies, it may be alcohol, oil, mineral spirits, etc. If you put in the wrong one, you'll muck things up. If you want to top it up, ask the maker what the correct fluid is (many sell it) or ask them for the MSDS on the fluid tha tthey sell--they are required to provide an MSDS for any "chemicals" shipped interstate. And change the o-ring or other reason that your compass leaked, as well.
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I filled mine with Gin, now it always points to the tonic.
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I would think that the gimball would have enough weight to counteract in magnetic forces in a compass.
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Old 04-27-2009
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Quote:
Originally Posted by MoonSailer View Post
I would think that the gimball would have enough weight to counteract in magnetic forces in a compass.
The "un-balanced card" is a known element in steering compasses. Here is a process of swinging a compass that about halfway down the page deals with hemispherical lean on the card. Here is a comment by Roy McBride:

"Every boat needs a compass if it intends doing coastal or offshore work,its not just a job of taking the new (or old) compass from its box and bolting it down,certain things must first be done,here are a few pointers (no pun intended)the first thing to check is if the unit you have is a northern or southern hemisphere compass? This is due to the pull of the worlds magnetic field being different at each side of the equator,this means the compass card will show a lean or 'pull' on a compass fitted in England but now having traveled to South Africa. Normally the card tilt is just a bother but in some cases the card can actually stick,then its a worry,assuming we understand that side of things we can move to the next issue."

And I could find many more - I'm just not interested enough. I'm also not clever enough to make up a story like that.

For the whole article on swinging your own compass see:

CKD Boats - Roy Mc Bride: Compass Swinging for yachts,you can do it yourself
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Old 04-29-2009
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You are right!!! I guess that dip is a stronger force than I thought. I knew that dip affected compasses but thought that the gimball weight was enough. It is good to learn..thanks.
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Old 04-29-2009
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I have run into ethylene glycol before.

Quote:
Originally Posted by hellosailor View Post
Some compass makers offer very reasonable repair or replacement services, so first call the maker.

Compass fluid varies, it may be alcohol, oil, mineral spirits, etc. If you put in the wrong one, you'll muck things up. If you want to top it up, ask the maker what the correct fluid is (many sell it) or ask them for the MSDS on the fluid tha tthey sell--they are required to provide an MSDS for any "chemicals" shipped interstate. And change the o-ring or other reason that your compass leaked, as well.
As material compatibilities go, it is either petroleum (mineral oil) or aqueous (alcohol/glycol/glycol ether). So, does the existing fluid mix with water? Simple.

If it is aqueous, best dump it all and use fresh EG or glycerine, mixed 50/50 with water.
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Old 04-29-2009
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Quote:
Originally Posted by Omatako View Post
The "un-balanced card" is a known element in steering compasses. Here is a process of swinging a compass that about halfway down the page deals with hemispherical lean on the card. Here is a comment by Roy McBride:

"Every boat needs a compass if it intends doing coastal or offshore work,its not just a job of taking the new (or old) compass from its box and bolting it down,certain things must first be done,here are a few pointers (no pun intended)the first thing to check is if the unit you have is a northern or southern hemisphere compass? This is due to the pull of the worlds magnetic field being different at each side of the equator,this means the compass card will show a lean or 'pull' on a compass fitted in England but now having traveled to South Africa. Normally the card tilt is just a bother but in some cases the card can actually stick,then its a worry,assuming we understand that side of things we can move to the next issue."

And I could find many more - I'm just not interested enough. I'm also not clever enough to make up a story like that.

For the whole article on swinging your own compass see:

CKD Boats - Roy Mc Bride: Compass Swinging for yachts,you can do it yourself
Does that mean you need two compasses if you sail in both hemispheres ?
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