There was some earlier discussion about how the vertical component of the changes in the magnetic field can mess up "Silva" type land compasses when they're used in latitudes other than the one they're manufactured for. For this very reason, one company recently introduced the "Global" hand held compass, in which the needle, in addition to being pivoted, is gimbaled, so that it can balance throughout the world. (Interest to declare: my employer sells the "Global", but I'm not mentioning it here for that reason, but rather because of its relevance to the next question. Besides which, I don't think the "Global" is of much interest to buy for sea kayakers.) Anyway, the question was raised whether sailing compasses could or should be adjusted some how when used in different latitudes. I've never read of anyone doing this, and I believe it's because marine compasses are highly "gimbaled" anyway to allow for listing, and so would not be affected by the vertical changes. Comments? Philip Torrens "The opinions expressed here are not necessarily those of my employer, or indeed, of any sentient being." **************************************** Mountain Equipment Co-op 1655 West 3rd Avenue, Vancouver, BC, Canada V6J 1K1 Tel: 640-732-1989 Fax: 604-731-6483 email: pid_at_mec.ca Visit our website at: http://www.mec.ca ***************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
> Anyway, the question was raised whether sailing compasses could or > should > be adjusted some how when used in different latitudes. I've never read > of > anyone doing this, and I believe it's because marine compasses are > highly > "gimbaled" anyway to allow for listing, and so would not be affected > by the > vertical changes. Comments? > I was reading one of Lynn & Larry Pardee's (sail) cruising books recently. In it they mentioned having navigational problems when reaching the South Pacific (I think) from somewhere north. They would take their celestial sightings, plot their course and be consistantly (dangerously) off course by a few degrees. When they checked, all of their compasses were off so it wasn't a magnetic problem. Apparently this was their first time having crossed the equator (or whatever) and someone told them about the compass variance. They went to a professional compass adjuster and the problem was soon recticified. Apparently the adjustments are fairly complex and/or delicate. I don't remember all the specifics but I am sure of the context. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
From: "Sisler, Clyde" <Clyde.Sisler_at_wang.com> To: "'Paddlewise'" <paddlewise_at_lists.intelenet.net> Subject: RE: [Paddlewise] compasses in different latitudes Date: Mon, 8 Jun 1998 13:12:37 -0400 > Anyway, the question was raised whether sailing compasses could or > should > be adjusted some how when used in different latitudes. I've never read > of > anyone doing this, and I believe it's because marine compasses are > highly > "gimbaled" anyway to allow for listing, and so would not be affected > by the > vertical changes. Comments? > Also in "My Old Man and the Sea" -- a book about a father and son cruising around the horn in a 25' or so sailboat, they talk about having compass problems once they cross the equator, so the problem seems to happen to sailing compasses also. Even with a gimbal, the compass plate might get out of balance if the magnetic field is pulling down harder on one side than the other. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
It is not quite that easy. The magnetic field is curved and the actuall magnetic poles are not at the surface of the earth so you need a compass that is compensated for the part of the world you are going to be in. Compass makers rate their compasses for 'zones' and will be happy to tell you what their zones are and how much out of the zone you can go. A compass that is great at 50 deg North will be nearly useless at 50 South, This is just too far out to work well. If you must go from far North to far South in one trip, either carry comapsses for both hemispheres or go to a good fluxgate compass that does the compensation in the computer. BTW When you get real close to the pole (magnetic) the compass just spins, then you use a sun compass. :-) michael pid_at_mec.ca wrote: > > There was some earlier discussion about how the vertical component of the > changes in the magnetic field can mess up "Silva" type land compasses when snip > anyone doing this, and I believe it's because marine compasses are highly > "gimbaled" anyway to allow for listing, and so would not be affected by the > vertical changes. Comments? *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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