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Compass dip - questions for the southern Hemisphere people.
The first answer was the closest. Yes there is a difference and yes in most
compasses including the one's we find on our sailboats and powerboats are, in fact, different. Some compasses, such as the one on USNS Bob Hope, are built to be self adjusting when crossing the line. On a previous ship one of our main bridge compasses (magnetic not gyro) showed a marked tilt some degrees south of the equator. It was recalibrated in Darwin, Australia. Great seafood buffet place down there by the way. Smaller less expensive compasses do not have this ability for self adjustment and this includes those in the many hundreds of dollars category. No need since most boats don't make it across the equator one way or another. The easiest way to solve the issue is order up a compass from some company in Australia, NZ etc. and have it airmailed. Get the exact same compass you already have. When crossing the equatorial region at some point you will observe the tilt or dip. Switch compasses and re-swing. Not hard to do even way out there. In fact I think it was Ole Thom who first gave me an explanation on how to determine exact bearings out of sight of land. This phenomenae does not happen exactly at the equator. The reason it happens is the distance from the mass of iron in N. Canada that is the Magnetic Northern Pole increases while the mass of earth's iron making up the Magnetic Southern Pole decreases in distance. At some point one becomes the major attraction to ye olde compass instead of the other and it becomes off-balance. Here's the humorous part. When the compass on our ship acted up none of the highly trained and experienced deck officers realized what had happened. One of the other AB's remarked to me, "Southern Dip?" "For sure", sez I. Finally we were asked what we meant by that phrase. They didn't believe us and had to look it up in Bowditch. Score one for the home team! Three more days and we're outta here. OT is running 4 plus hours a day and tomorrow for T-Day we will work about 12. You all enjoy the turkey . .. I'm loving the paycheck! Here's one for you. The new Chief Mate on board has the unlikely name of Despot.She just finished being Captain of a smaller vessel and is now qualifying in the big ones. Yes, I did say 'she'. Imagine "Captain Despot" being your boss. Haggie, Katy, LP don't worry about ole Neale . . . .Your gender is more than holding it's own in the commercial mariner's world. The best part is it's no longer necessary out here for someone to say, "How do you find working for a woman?" The question never comes up. But it's kinda fun knowing I work for a 'Despot'. Few more days and I'll talk to you all in two months or so . . . . MST |
#2
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Compass dip - questions for the southern Hemisphere people.
Great and informative post. Thanks. It's nice to see some
people around here are more interested in providing in- formation instead of only trying to belittle and build up their own sagging egos (Oz). Your observations pretty much confirm my suspicions about compasses and nobody's mentioning dip in their world cruises. It also confirms what I know about deck officers like those who frequent this group - they know little about what we sailors know instinctively because we are so close to the water and the real world in comparison. Fair winds to ya. Enjoy your mission. S.Simon "Schoonertrash" wrote in message ... The first answer was the closest. Yes there is a difference and yes in most compasses including the one's we find on our sailboats and powerboats are, in fact, different. Some compasses, such as the one on USNS Bob Hope, are built to be self adjusting when crossing the line. On a previous ship one of our main bridge compasses (magnetic not gyro) showed a marked tilt some degrees south of the equator. It was recalibrated in Darwin, Australia. Great seafood buffet place down there by the way. Smaller less expensive compasses do not have this ability for self adjustment and this includes those in the many hundreds of dollars category. No need since most boats don't make it across the equator one way or another. The easiest way to solve the issue is order up a compass from some company in Australia, NZ etc. and have it airmailed. Get the exact same compass you already have. When crossing the equatorial region at some point you will observe the tilt or dip. Switch compasses and re-swing. Not hard to do even way out there. In fact I think it was Ole Thom who first gave me an explanation on how to determine exact bearings out of sight of land. This phenomenae does not happen exactly at the equator. The reason it happens is the distance from the mass of iron in N. Canada that is the Magnetic Northern Pole increases while the mass of earth's iron making up the Magnetic Southern Pole decreases in distance. At some point one becomes the major attraction to ye olde compass instead of the other and it becomes off-balance. Here's the humorous part. When the compass on our ship acted up none of the highly trained and experienced deck officers realized what had happened. One of the other AB's remarked to me, "Southern Dip?" "For sure", sez I. Finally we were asked what we meant by that phrase. They didn't believe us and had to look it up in Bowditch. Score one for the home team! Three more days and we're outta here. OT is running 4 plus hours a day and tomorrow for T-Day we will work about 12. You all enjoy the turkey . .. I'm loving the paycheck! Here's one for you. The new Chief Mate on board has the unlikely name of Despot.She just finished being Captain of a smaller vessel and is now qualifying in the big ones. Yes, I did say 'she'. Imagine "Captain Despot" being your boss. Haggie, Katy, LP don't worry about ole Neale . . . .Your gender is more than holding it's own in the commercial mariner's world. The best part is it's no longer necessary out here for someone to say, "How do you find working for a woman?" The question never comes up. But it's kinda fun knowing I work for a 'Despot'. Few more days and I'll talk to you all in two months or so . . . . MST |
#3
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Compass dip - questions for the southern Hemisphere people.
Schoonertrash wrote:
The first answer was the closest. Yes there is a difference and yes in most compasses including the one's we find on our sailboats and powerboats are, in fact, different. Some compasses, such as the one on USNS Bob Hope, are built to be self adjusting when crossing the line. Sounds like a good but probably expensive feature to have. .... The easiest way to solve the issue is order up a compass from some company in Australia, NZ etc. and have it airmailed. Get the exact same compass you already have. Actually, you don't need to order from Australia (not intending to hurt the Aussie economy, sorry). All good compass makers will have the same model compass made in several dip ranges. The dip angle changes by latitude, not just when you cross the equator. When crossing the equatorial region at some point you will observe the tilt or dip. Switch compasses and re-swing. ..... The reason it happens is the distance from the mass of iron in N. Canada that is the Magnetic Northern Pole increases while the mass of earth's iron making up the Magnetic Southern Pole decreases in distance. At some point one becomes the major attraction to ye olde compass instead of the other and it becomes off-balance. Total malarkey. Compasses are polar, north poles & south poles of magnets both attract metal but only opposite poles of other magnets. Try it yourself with a kids toy bar magnet. The reason for the dip angle is that the Earth is round (well, it's an oblate sphere) and the lines of magentic force between the North and South Poles are more apple-shaped. So, the Earth's magnetic field pulls either the north or south pole of the compass card down more as it approaches the poles. Here's the humorous part. When the compass on our ship acted up none of the highly trained and experienced deck officers realized what had happened. One of the other AB's remarked to me, "Southern Dip?" "For sure", sez I. Finally we were asked what we meant by that phrase. They didn't believe us and had to look it up in Bowditch. Score one for the home team! I guess if you don't think about a compass very often, you forget stuff like that. I can't believe a qualified sea officer would have never learned about compass dip. For that matter I am surprised you can't explain it more clearly & accurately yourself, ST! Fresh Breezes- Doug King |
#4
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Compass dip - questions for the southern Hemisphere people.
Well . . it was clear to me?????
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#5
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Compass dip - questions for the southern Hemisphere people.
Subject: Compass dip - questions for the southern Hemisphere people.
From: "Schoonertrash" Date: 11/28/2003 18:52 Pacific Standard Time Message-id: Well . . it was clear to me????? I'd be curious as to what they had to do in Australia to fix the "dip" problem, plus, curious how they "balance" small yacht compasses to make them good, world wide. |
#6
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Compass dip - questions for the southern Hemisphere people.
As Doug mentioned the cost of doing that is prohibitive. Much easier to get
two compasses. When you see the need, and it will be very apparent. Switch to the other one. Then you only have to swing the compass for correction which is not all that difficult. Remember you now have things like GPS to help you out. Or use a star sight for N. and S. Figure amplitude on the sun's rising and setting to find E. and W. Sounds much more intimidating that it really is. MST One day left. |
#7
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Compass dip - questions for the southern Hemisphere people.
Schoonertrash wrote:
Well . . it was clear to me????? Massive iron deposis in Canada have nothing at all to do with compass dip. It's only that the earths surface is not parallel to the lines of the Earths magnetic force. Closer to the poles, the magnetism of the Earth pulls either the north or south pole of the compass down more. Close to the equator, the force is almost parallel. You may be thinking about variation, which is definitely affected by local magnetic anomalies like massive iron deposits. BTW in a couple of "around the world" sailing books, the skipper/author talks about either correcting for compass dip or switching compasses. One of them is 'My Old Man & The Sea' which is a good read all in itself; but they planned to take three compasses with them (on a 25' boat no less) and in the last minute rush, forgot. So they disassembled their compass and remounted the magnets to correct for dip. Interesting book, I gave my father a copy..... Fresh Breezes- Doug King |
#8
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Compass dip - questions for the southern Hemisphere people.
DSK wrote: Massive iron deposis in Canada have nothing at all to do with compass dip. It's only that the earths surface is not parallel to the lines of the Earths magnetic force. 100% correct. Closer to the poles, the magnetism of the Earth pulls either the north or south pole of the compass down more. Close to the equator, the force is almost parallel. Not really, the region of zero dip wanders about 12 degrees north and south of the equator. Check out Chart 30 for this info? You may be thinking about variation, which is definitely affected by local magnetic anomalies like massive iron deposits. Dip is also affect by anolmalies. Cheers MC |
#9
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Compass dip - questions for the southern Hemisphere people.
"Simple Simon" wrote in message ...
Since the north magnetic pole is not resting upon the surface of the Earth compasses made for Northern Hemisphere use are usually weighted on the card on the southern side to keep the card more level as the north side of the card seeks out the north pole buried well inside the Earth. Ever see a chart of the magnatic field of the earth? Seems to me the weight used to hold the card level-upright is effected by gravity not magnetics. Are the compasses you Australian and New Zealand ******s use weighted any differently? What if you were going to sail to Canada or something. Would your southern compass work in the Northern hemisphere? Also does you compass really seek the North magnetic pole or is it made backwards to seek the south magnetic pole. What I want to know is: Do seashells grow clockwise in the s. hemisphere? How about barley twist canes? And in the S. Hemisphere will you Neil swirl your ceder bucket the other way?. Joe MSV RedCloud .......With a Counter Clock wise flushing head. Enquiring minds want to know . . . S.Simon |
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