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Thread: Compass ajustment

  1. #1
    Join Date
    Nov 2001
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    Odessa, Ontario, Canada
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    Default Compass ajustment

    Hello,

    Does anyone know of any good resources on compass adjustment? Whether it be books or online.

  2. #2
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    May 2012
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    Default Re: Compass ajustment

    https://www.amazon.com/Ships-Compass.../dp/0710065221

    The Ships Compass is the adjusters bible. A weighty tome, may not be what you're after if you just need your compass to be true.

  3. #3
    Join Date
    Apr 1999
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    Hyannis, MA, USA
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    Default Re: Compass ajustment

    Depends on how bad things are. Do you want to avoid the expense of a pro.

    Can you move the compass? If you can, do some bearings on shore objects that line up to get an idea of where the compass is closest to true. Then proceed with adjustment and/or a deviation card.

  4. #4
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    Nov 2001
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    Odessa, Ontario, Canada
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    Default Re: Compass ajustment

    Thank you for the suggestion. I will get a copy of The Ships Compass, it looks like what I am looking for.

  5. #5
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    Default Re: Compass ajustment

    Glad to help, but be warned, it is full of basic and advanced magnetic theory, mathematics and fomulae, around 250 pages of it. It is meant for more than just tuning up one's own compass, but for the would be adjuster it is the go-to text. Good luck.

  6. #6
    Join Date
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    Odessa, Ontario, Canada
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    Default Re: Compass ajustment

    Thank you, that is very much what I am looking for.

  7. #7
    Join Date
    Jun 2006
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    Blacksburg, VA
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    Default Re: Compass ajustment

    Although I've never seen Ships Compass, I expect that it is directed largely at compensation for compasses on steel ships. If you have a wooden boat with no large hunks of iron or un-twisted DC wires near the compass you have much less to worry about. There are fairly extensive instructions on compass installation, adjustment, and use in Chapman Piloting and Seamanship​.
    I will beg you for advice, your reply will be concise, and I will listen very nicely and then go out and do exactly what I want! (Apologies to Lerner and Lowe.)

  8. #8
    Join Date
    Dec 2010
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    Ohio USA
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    Default Re: Compass ajustment

    FYI no matter how much you try to compensate for the magnetic deviation of your boat it will not work for all headings.

    You will still need to create a deviation table for your boat and use it to calculate from True to Compass and Compass back to true.

    T True (Chart Course)
    V Variation (based on the location you are- the difference between True North and Magnetic North)
    Makes Magnetic Heading of the boat used to look up you deviation
    Dull Deviation of you boat at your heading
    Children Compass (Your boats compass heading)
    Add Water Add West when going from top to bottom.

    Here is a simple image showing
    1. Variation is based on location (Chicago is different than New York)
    2. Deviation is based on your boats heading.
    The black dot on the boat represents the total magnetic field of your boat.
    Sometime the magnetic field on your boat will pull the compass to the right of magnetic north and sometimes to the left of magnetic north.

    TVMDC.jpg

  9. #9
    Join Date
    Nov 2004
    Location
    Port Townsend WA
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    14,445

    Default Re: Compass ajustment

    Quote Originally Posted by alkorn View Post
    Although I've never seen Ships Compass, I expect that it is directed largely at compensation for compasses on steel ships. If you have a wooden boat with no large hunks of iron or un-twisted DC wires near the compass you have much less to worry about. There are fairly extensive instructions on compass installation, adjustment, and use in Chapman Piloting and Seamanship​.
    A commercial ships compass often has a pair of adjustable iron spheres on either side. These were invented by Lord Kelven who came up with the idea back in the 1880s that is known as "Lord Kelven's Balls". Today, a compass compensater will "swing" a Yacht's compass by comparison to known sighting lines or the location of Venus or the sun at noon if visible at a given time and mount appropriate compensating magnets near the compass. But he or she will also takes the boat's wiring in mind and may add deviation or variation information as to what amount of addition or subtraction of degrees for a given course in a heading that may be needed to effect an accurate course to steer. In some local areas certain changes in magnetic attraction can vary and so it is wise to investigate the possibility of such if you are not sure of what may be lurking under your binnicle or such as a new engine or, as in times past, a magnetic case of beer! I refer to beer in steel cans as I was once on a race that had just such a situation occur that nearly put us on the rocks at night on one of the Channel Islands off the California coast!
    Jay
    Last edited by Jay Greer; 04-06-2020 at 04:08 PM.

  10. #10
    Join Date
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    Default Re: Compass ajustment

    In '66 I crewed for a wealthy publisher. He'd had a larger engine installed, a bigger Onan genset, and machinery for AC, freezer, 'fridge, and tons of other stuff. All got too close to the compass let into the bridge deck so the compass was really deviant. Among his many collectables, the publisher had a nice gimbaled dumb compass with a three vanes to use as a pelorus. I used the center vane to cast a shadow, rotated the unit so the shadow fell where the almanac said it should, and worked on a deviation table to start the adjustment process. Got it as close as possible but the installation required three deviation tables: sailing engine off; engine on; and both engine and radar on.

  11. #11
    Join Date
    Dec 2010
    Location
    Ohio USA
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    Default Re: Compass ajustment

    Quote Originally Posted by Ian McColgin View Post
    In '66 I crewed for a wealthy publisher. He'd had a larger engine installed, a bigger Onan genset, and machinery for AC, freezer, 'fridge, and tons of other stuff. All got too close to the compass let into the bridge deck so the compass was really deviant. Among his many collectables, the publisher had a nice gimbaled dumb compass with a three vanes to use as a pelorus. I used the center vane to cast a shadow, rotated the unit so the shadow fell where the almanac said it should, and worked on a deviation table to start the adjustment process. Got it as close as possible but the installation required three deviation tables: sailing engine off; engine on; and both engine and radar on.
    I never though of that, thanks for making a very good point.
    "The only rules that really matter are these: what a man can do and what a man canít do." Captain Jack Sparrow

  12. #12
    Join Date
    Mar 2018
    Location
    Southwest Iowa, USA
    Posts
    24

    Default Re: Compass ajustment

    Don't forget the Flinders bar on the big steel ships, which compensates for inherent vertical magnetism. Unless you're on my first ship, where it was inexplicably missing.

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