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Old 09-04-2011, 12:31 PM   #21
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RE: compass

Quote:
KJ wrote:*
According to Bowditch:
*
*"After a ship (boat) is launched, over time, it will lose some of *its original magnetism.**...

*I had suspicion that some "degaussing" could occur over time.
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Old 09-04-2011, 12:34 PM   #22
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RE: compass

I've not used my compass very much but when I have I'm grateful It's stable. All the compasses Iv'e used before have been almost impossible to read/follow/use. Not so w the compass on my Willard and I do think it's the original. I don't know if it could be improved upon. Sometimes I wonder if the damping and reaction rates should be idealized to each boat as they all have different motion. I went half way across Dixon Entrance in a thick fog (six miles offshore) steering by the compass and found it was easy to do. It was frustrating w the GPS. The compass required constant attention but as long as my attention didn't wander (and my attention tends to do so) steering w the compass Willard provided is safe and easy to do. But most of the time I don't even even look at the GPS compass ....just the chart and "noodle" (I think cursor) as Marin calls it. And on rare occasions when the cursor or noodle goes over land on the chart I'm not worried as I can see that I'm not.
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Old 09-04-2011, 06:57 PM   #23
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RE: compass

That first year of navigation could be a tough one.
What ever happened to re swing the compass? An argument not to correct in the first year is hardly good seamanship. A post accident marine inquiry would be hard to defend with "My builder told me I didn't have to swing it for the first year" An unseaworthy vessel can be cause for insurance denial.
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Old 09-04-2011, 08:37 PM   #24
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RE: compass

I keep my compass calibrated, if for no other reason than to estimate the wind direction.
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Old 09-04-2011, 10:19 PM   #25
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compass

Quote:
Sailor of Fortune wrote:
That first year of navigation could be a tough one.
What ever happened to re swing the compass? An argument not to correct in the first year is hardly good seamanship. A post accident marine inquiry would be hard to defend with "My builder told me I didn't have to swing it for the first year" An unseaworthy vessel can be cause for insurance denial.
*I do have several other "compasses" aboard (flux-gate, GPS, binocular, and handheld) and radar and don't intend to leave the sight of land in the near future.


-- Edited by markpierce on Sunday 4th of September 2011 10:32:31 PM
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Old 09-05-2011, 06:18 AM   #26
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RE: compass

Quote:
markpierce wrote:
*I do have several other "compasses" aboard (flux-gate, GPS, binocular, and handheld)...
*Mark:* If you put the handheld compass in the area that your regular compass is installed, does it just read S-SW?* I think you said you binoculars also only read S-SW.* If they all read the same, you have some magnetic interference some where.
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Old 09-05-2011, 01:36 PM   #27
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RE: compass

Larry, I intend to test the portable magnetic compasses in different areas of the boat.* By the time the Coot gets out of the boatyard and I go on my two-week transatlantic cruise (Norwegian Sun), it will be well into October before the tests.
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Old 09-05-2011, 03:26 PM   #28
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RE: compass

Just make sure that Norwegian Sun has a good, working, magnetic compass on it before you ship out!
Bon voyage
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Old 09-05-2011, 04:11 PM   #29
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RE: compass

Thanks, Steve.* The Norwegian Sun has been refitted since my 2009 Alaskan voyage (the one where heavy fog cancelled entry into Tracy Arm) on her.* Trusting the revisions didn't mess up its compass.

Entry into Tracy and Endicott Arms on a clearer day in 2011.* Ended up in Endicott Arm since Tracy was overfilled with other cruise ships.* This was second time advertised destination was cancelled!

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Old 09-05-2011, 07:04 PM   #30
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compass

Quote:
Sailor of Fortune wrote:
That first year of navigation could be a tough one.
What ever happened to re swing the compass? An argument not to correct in the first year is hardly good seamanship.
*
While a boat is being built it will acquire "induced" magnetism from the construction itself, as well as the local magnetism of the area of the yard. This induced magnetism is not part of the boats "permanent" magnetism. A deviation table could be in error if established while the foreign induced magnetism is still influencing the boat. *It can take some time for the boat and the compass to become adjusted to the area in which the boat will be finally used.
The skipper or navigator should be checking the deviation every time the boat is used and record the deviation at different headings. *The locally induced magnetism, i.e., sitting in her own slip for a period of time, will become part of the boats permanent magnetism. Eventually the table should stabilize.
If you rely mainly on your compass for navigation, you should have a professional "swing ship", which should give your compass a pretty high degree of accuracy which then should be quite reliable. Back-up compasses should be used for rough estimates of position, never for precise navigation. ***

*

*

*
*****

*



*


-- Edited by KJ on Monday 5th of September 2011 08:00:06 PM
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Old 09-06-2011, 03:42 AM   #31
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RE: compass

Our method ( if off the AP) is to use a QUALITY hand held compass to obtain the course, and then use the "main compass" to steer with .

It is frequently easier to check the hand bearing unit than the main as it can be read on a mark much closer.
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Old 11-10-2011, 05:52 AM   #32
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RE: compass

Quote:
markpierce wrote:
*...both my boat's regular magnetic compass as well as the binocular compasses read only between S and SW regardless of the boat's direction.* (The engine is behind and to the left of the compass.)* The boat's builder said not to bother compensating the compass before a year has passed.

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Mark:* Did you*get your compass to read correctly?** What was the problem?
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Old 11-10-2011, 06:36 AM   #33
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RE: compass

Welding and hammering on a steel hull during construction aligns the magnetic domains in the steel with the local lines of magnetic flux. If you wait long enough normal stresses and strains will realign them to the area you normally operate. That is why the builders said to wait a year. That and the fact that they would have had to pay the compass adjuster.

If you are in a hurry, do it like the V-1 buzz bomb crews did and line the boat up on a known heading and beat the hull with rubber hammers for a while.

There is no reason not to swing the compass now. It shouldn't be done at the dock and it really should be done by a compass adjuster. As the boat ages and gets knocked around a bit the compass error will increase again and it will need to be swung again if accuracy matters, as it should and certainly will when you lose power to all those nice displays in the fog while cruising the Bay. At the very least make a correction card try to keep it up to date.
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Old 11-10-2011, 10:48 AM   #34
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RE: compass

Since we have a great compass discussion I thought I should mention auto pilot compasses. I go out on so many different boats each year and I often see that the auto pilot compass does not agree with the main compass, and that often does not agree with the GPS. The GPS is of course actually a history but it will be the most accurate. Often when on a sea trial for a survey the surveyor will report metal or magnetic items have been stowed near the auto pilot compass and often they will suggest to re-calibrate the auto pilot compass every few years. You can check your owners manual to see what settings to use while doing a simple circle.
It is not that often that I see a compass deviation card on board now except for older boats and long distance trawlers.
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Old 11-10-2011, 10:55 AM   #35
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RE: compass

If you have an Auto pilot it is a great way to save on the fuel bill.

Shortest distance between two points is a straight line.

Ever watch your wake after hand steering for a while. It's hard to keep her straight what with wind and current.

If turned on the auto is working like a son of a gun making minute corrections.

I love it.

SD
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Old 11-10-2011, 10:58 AM   #36
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RE: compass

I thought "swinging the compass" was to compensate for all the magnetic things on the boat. All boats have their magnetic things (disturbances) in different places and there'fore the compass needs the compensating magnets to be adjusted so as to cancel out the disturbances such as the engine, stove and all other magnetic things in the boat. The older compass's had the compensating magnets outside the compass usually in the form of 2 balls about 1.5 to 2" in diameter on each side of the compass. So I do'nt see how one could take a compass to a shop and get it compensated. Perhaps I'm not understanding this correctly.
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Old 11-10-2011, 11:11 AM   #37
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RE: compass

Swinging the Compass

1) Locate two transit objects (objects in line) and determine their true bearing on the chart
(2) Secure the boat at anchor so that these transits are exactly aligned. Swing the boat's head until it is pointing due north.
(3) Read off the transit bearing on the compass and apply the variation.
(4) The difference between this result and the true transit bearing is the deviation on this heading. If the true bearing is greater, the deviation is named east; if it is the lesser, the deviation is named west.
(5) Repeat the procedure taking transit bearings on each of the cardinal points.
(6) From the results, make up a deviation card
Further errors are caused by boat heel, and the difficulty of reading when on a moving platform. An electronic compass can be set up to remove the effect of deviation, but it is still a magnetic compass.
Hand bearing compasses usually show very small deviation effects which can be ignored if you use them away from a magnetic area.
Deviation can also be East or West, but the same logic applies:
Sounds simple but try it once.
SD
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Old 11-10-2011, 12:13 PM   #38
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RE: compass

Quote:
nomadwilly wrote:
I So I do'nt see how one could take a compass to a shop and get it compensated. Perhaps I'm not understanding this correctly.
* * * ** The shop person comes to your boat....you take the boat out in calm water and initiate a circular turn (either direction) while he/she adjusts the ship's compass. This is done several times until the person doing the adjusting is satisfied with the process. They then give you a correction card to store by your compass for navigating.
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Old 11-10-2011, 12:31 PM   #39
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compass

Quote:
SeaHorse II wrote:
The shop person comes to your boat....
*I would truly love that but I can't find a compass guy that will travel to where my boat is.

As a matter of fact there isn't anybody in South Central Alaska that even works on compasses.

I have tried google and all the phonebooks. One guy in Kodiak but he doesn't leave the Island

So Gotta figure it out myself.

SD


-- Edited by skipperdude on Thursday 10th of November 2011 01:42:20 PM
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Old 11-10-2011, 12:41 PM   #40
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RE: compass

Quote:
skipperdude wrote:
*I would truly love that but I can't find a compass guy that will travel to where my boat is.
* * * * Sorry SD...point taken.
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