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Old 30-04-2013, 05:14   #16
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Re: Handbook of Magnetic Compass (H.O. 226)

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Originally Posted by carstenb View Post
I'm old-fashioned too. Every year at the start of the season, I check the deviation of my compass at all points of the compass (and log it!).

Why?

Because you never know.......................
Except, that having done so; you DO know.
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Old 30-04-2013, 05:17   #17
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Re: Handbook of Magnetic Compass (H.O. 226)

To clarify, I must say the above is based on the presumption of current paper charts onboard. Friends don't let friends sail without paper.
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Old 30-04-2013, 05:19   #18
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Re: Handbook of Magnetic Compass (H.O. 226)

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Except, that having done so; you DO know.
In context, succinct and wise. How do you do it?
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Old 30-04-2013, 06:17   #19
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Re: Handbook of Magnetic Compass (H.O. 226)

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I think Deperning has the same meaning as Degausing, a process used to de-magnetise a ship. Very commonly used during WW2 to protect ships from magnetic mines.
I'm old enough to remember that the first two ships I went to sea on were fitted with degausing coils around the main deck. These were cargo ships built during the 1960's.
By the 80's most of the copper coils had ended up being hacked off by the crew and sold as scrap.
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They just took it down, but out at the end of Copenhagen Harbour that were 4 yellow buoys that marked the Degaussing station. Ships would sail into the area between the buoys and ZAP! the station on shore would degauss them.

It was still in use about 5 years ago
Deperming and degausing are not the same. Degausing coils are built into the ship, and powered up to reduce the induced magnetism, so as to not activate magnetically-triggered mines. I imagine that only warships are so fitted these days.
Deperming is done (very infrequently) by wrapping a huge wire coil around the outside of the ship - when energized this removes the subpermanent magnetism.

The station in Copenhagen does not degause ships - it measures the magnetic signature of ships passing over it, to test the effectiveness of the degaussing equipment. When a ship "fails" such a test, it is a good indication that the ship needs to be 'depermed.'
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Old 30-04-2013, 06:24   #20
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Re: Handbook of Magnetic Compass (H.O. 226)

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Deperming and degausing are not the same. Degausing coils are built into the ship, and powered up to reduce the induced magnetism, so as to not activate magnetically-triggered mines. I imagine that only warships are so fitted these days.
Deperming is done (very infrequently) by wrapping a huge wire coil around the outside of the ship - when energized this removes the subpermanent magnetism.

The station in Copenhagen does not degause ships - it measures the magnetic signature of ships passing over it, to test the effectiveness of the degaussing equipment. When a ship "fails" such a test, it is a good indication that the ship needs to be 'depermed.'
Thank you for your comments. But while you state that deperming and degausing are not the same and you state how deperming is accomplished you do not state why deperming is done. Please elucidate.
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Old 30-04-2013, 06:56   #21
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Re: Handbook of Magnetic Compass (H.O. 226)

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Nyet. A GPS is not required. I suspect you know that many ports have range markers, et al which accurately define a true course. Mark your heading in reference and note deviation. 16 points indeed is doable and warranted.

EDIT: didja know typing "point" without the "O" makes me thirsty? Thank God my compulsion to proofread before I hit SEND.
You're righta GPS is not required. But for a lot of people using the GPS is much simpler etc. If you're really into all that (I learned how when I took my Yachtmaster ), you can get your sextant out and go to town.

After that 16 PINTS is indeed both warranted and doable
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Old 30-04-2013, 09:29   #22
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Re: Handbook of Magnetic Compass (H.O. 226)

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I forgot to ask, until now: who, when commissioning or taking possession of a used vessel for recreation (non-commercial), thinks to swing the compass?
I did on our steel cutter, as the Ritchie Globemaster is too nice not to consult on a regular basis!

As I've removed an antique sounder CRT unit, I will have to swing it again soon, if only so I have reason to utter the always amusing phrase "compensator balls".
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Old 30-04-2013, 10:09   #23
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Re: Handbook of Magnetic Compass (H.O. 226)

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As I've removed an antique sounder CRT unit, I will have to swing it again soon, if only so I have reason to utter the always amusing phrase "compensator balls".

Over here they are affectionately known as "Kelvins balls", after Lord Kelvin who I believe came up with the concept.
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Old 30-04-2013, 10:29   #24
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Re: Handbook of Magnetic Compass (H.O. 226)

There used to be a 'degausing' range in San Diego Harbor and I suspect in a number of WWII ports around the world. With the advent of more sophisticated electronic gear and gyros, the practice of degausing has not been too rigorously followed of late from what sailors out of San Diego (OOD's) tell me.
On the other hand, a good friend of mine from San Diego who purchased a new (to him) Hans Christian 43 that used to be berthed in Morro Bay, CA brought her down and had the former owner crew for him on the trip becuase he was told they would have to hand steer the whole way. The autopilot which had been installed was not working for some unknown reason.
After owning her for a couple of months and getting used to the quirks of sailing a new boat, he asked me to have a look at the autopilot. We took her out one afternoon, turned on the autopilot and she just sailed in circles so back at he dock, I began checking out the autopilot installation. It was fine but the old owner had also bought new VHF and installed it right next to the autopilot fluxgate compass head. I removed the autopilot compass and re-installed it amidships low in the boat and away from any electrical interference. Took the boat out and the autopilot worked like a dream! Sorry for the thread drift but good idea to check for electrical interference on all your compass installations. Most install diagrams mention this... hope this helps someone, Phil
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Old 30-04-2013, 10:35   #25
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Re: Handbook of Magnetic Compass (H.O. 226)

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I did on our steel cutter, as the Ritchie Globemaster is too nice not to consult on a regular basis!

As I've removed an antique sounder CRT unit, I will have to swing it again soon, if only so I have reason to utter the always amusing phrase "compensator balls".
I logged on just to say...

...OMG, who do I have to kill to have a Ritchie! That is a work of art befitting any well found vessel. Your steel cutter sounds like just the right candidate.
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Old 30-04-2013, 10:43   #26
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Re: Handbook of Magnetic Compass (H.O. 226)

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You're righta GPS is not required. But for a lot of people using the GPS is much simpler etc. If you're really into all that (I learned how when I took my Yachtmaster ), you can get your sextant out and go to town.

After that 16 PINTS is indeed both warranted and doable
Do you take turning errors and speed changes into consideration? Kinda a dumass question but what the hey.
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Old 30-04-2013, 10:47   #27
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Re: Handbook of Magnetic Compass (H.O. 226)

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Hans Christian 43 that used to be berthed in Morro Bay, CA brought her down and had the former owner crew
Let me guess, a tall, thin blonde haired fellow with a red beard. I forget his name, it's been awhile.
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Old 30-04-2013, 11:15   #28
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Re: Handbook of Magnetic Compass (H.O. 226)

Not sure, Richard5, it was about 10-12 years ago and I didn't meet the old owner. The new one was from Salt Lake City, UT and was short, dark hair and clean shaven. The former owner had owned her up there for a number of years and I believe he lived aboard with his wife of partner. Phil
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Old 30-04-2013, 11:38   #29
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Re: Handbook of Magnetic Compass (H.O. 226)

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Over here they are affectionately known as "Kelvins balls", after Lord Kelvin who I believe came up with the concept.
I would have thought there was absolute zero chance of that being true...
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Old 30-04-2013, 12:15   #30
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Re: Handbook of Magnetic Compass (H.O. 226)

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Do you take turning errors and speed changes into consideration? Kinda a dumass question but what the hey.
I have to admit I'm not a complete nerd. I do keep a deviation chart though, you simply never know when you will be totally dependent on your compass (when all the electronics go down the toilet)
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