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Old 04-06-2018, 00:17   #61
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Re: true vs magnetic bearing

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Old 04-06-2018, 00:38   #62
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Re: true vs magnetic bearing

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With gps, I just set up to follow the gps correct course, and note what the magnetic compass indicates. Now I have a number to shoot for when steering by compass.
Ditto........
I sailed across the Pacific and up and down the South Pacific this way......
I know, I know, what happens when the electronics fail? I wander around until I hit something or starve is my plan.
I'm going to die of old age more than likely.
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Old 04-06-2018, 01:03   #63
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Re: true vs magnetic bearing

Hi together,
to answer xxhat`s question in a usable way, just rember something
we in Germany call course tower:

CC Compass course
+ DEV Deviation
= MC Magnetic course
+ DEK Declination
TC True course

If you have your compass course and want plot it in the map, just
add Deviation and Declination with the correct signand you have your
True course for the chart.

If you have TC out of the chart, just subtract DEK and DEV with the correct sign from TC and you know the Direktion to steer on the compass

Hope it helps.

John
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Old 04-06-2018, 02:36   #64
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Re: true vs magnetic bearing

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I don't know about this. I used to have issues with my handbearing hockey puck and the metal in my glasses.
Or sit next to the tiller pilot with a mobile phone in your pocket. An interesting experience in a busy shipping area I would rather not repeat.

Pete
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Old 04-06-2018, 08:28   #65
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Re: true vs magnetic bearing

Sometimes nearby rocks are just out to get you ... I was sailing down Revillagigedo Channel last year when my autopilot suddenly took a sharp turn to starboard ... what wasn't visible on the chartplotter, but was clearly printed on the paper chart in big pink letters Extreme magnetic disturbance, magnetic compass should not be relied upon.
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Old 04-06-2018, 08:55   #66
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Re: true vs magnetic bearing

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Originally Posted by Kelkara View Post
Sometimes nearby rocks are just out to get you ... I was sailing down Revillagigedo Channel last year when my autopilot suddenly took a sharp turn to starboard ... what wasn't visible on the chartplotter, but was clearly printed on the paper chart in big pink letters Extreme magnetic disturbance, magnetic compass should not be relied upon.
I wonder is the Navy doesn't have a degaussing station there?
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Old 04-06-2018, 09:45   #67
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Re: true vs magnetic bearing

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Sometimes nearby rocks are just out to get you ... I was sailing down Revillagigedo Channel last year when my autopilot suddenly took a sharp turn to starboard ... what wasn't visible on the chartplotter, but was clearly printed on the paper chart in big pink letters Extreme magnetic disturbance, magnetic compass should not be relied upon.
Our city is built upon an old iron ore mine. Magnetic variation of 50 degrees is not uncommon. My marina (Confederation Basin) in downtown Kingston (Lake Ontario, Canada) has an old steam engine as a heritage landmark/tourist attraction just a few metres from the shore. I am certain this huge piece of iron is a giant magnet, making my autohelm useless.

And yes, the waters near hear are filthy with old shipwrecks.
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Old 04-06-2018, 11:08   #68
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Re: true vs magnetic bearing

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Well put. Be nice to Antarcticans, too, as _your_ pole is pretty useless without theirs...
Conclusion: Be nice to all Poles!
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Old 04-06-2018, 13:43   #69
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Re: true vs magnetic bearing

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I wonder is the Navy doesn't have a degaussing station there?
I think you mean deperming station; degaussing stations only measure the magnetic signature of the ships - they don't create a magnetic influence.
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Old 08-06-2018, 09:54   #70
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Lightbulb Re: true vs magnetic bearing

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Originally Posted by xxhat View Post
I would appreciate it if someone explains how they use true or magnetic bearing for navigation.


I believe to use magnetic bearing I need to find the deviation of my compass ?


Thanks,


jim
TRUE bearing is where the boat is actually pointing.
MAGNETIC bearing is where the compass should say the boat is pointing, this varies across the globe, see paper chart for local magnetic variation.
DEVIATION is specific to your compass and will vary according compass heading.. It will depend on its location relative to other magnetic objects, eg, iron, steel and/or magnets. It needs to be added or subtracted from the magnetic variation.

As others have indicated, to find the DEVIATION on a particular compass you would need to do a compass swing, plenty of genuine info online....

Personally, in U.K. waters, I never bothered about the deviation as it was relatively little on my steering compass and over coastal passages, was less than the accuracy I could steer to with a tiller!

Bon Voyage!

Bony Tony.

P.s. I use paper charts and pencil, they donít suffer power cuts!
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Old 08-06-2018, 17:10   #71
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Re: true vs magnetic bearing

Canada owns the North Magnetic Pole not the north geographic pole. When using the North Magnetic Pole as a navigational reference is finally terminated because modern technology has rendered it obsolete (hopefully in the very near future) Canada will only own another piece of artic wasteland. Just kidding, the North Magnetic Pole has served us admirably for centuries. My thanks to Canada for letting us use it. Let's hope Canada erects a monument to it when it's no longer needed.
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Old 08-06-2018, 17:23   #72
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Re: true vs magnetic bearing

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Originally Posted by Cadence View Post
I wonder is the Navy doesn't have a degaussing station there?
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Originally Posted by Lodesman View Post
I think you mean deperming station; degaussing stations only measure the magnetic signature of the ships - they don't create a magnetic influence.
Neither are entirely correct and both refer only to ships etc. AFAIK, there is no way to alter natural magnetic anomalies in / on the earths surface (above or below water).
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Old 09-06-2018, 06:13   #73
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Re: true vs magnetic bearing

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Neither are entirely correct and both refer only to ships etc. AFAIK, there is no way to alter natural magnetic anomalies in / on the earths surface (above or below water).
Deperming isn't done to alter natural magnetic anomalies; it's done to remove induced magnetism from warships, so they will (hopefully) not set off magnetic-influence mines. It involves surrounding the ship with huge electric coils, and turning the ship into a giant electro-magnet. As you can imagine, a destroyer-sized magnet will have a significant local effect on magnetic compasses.
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Old 09-06-2018, 07:04   #74
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Re: true vs magnetic bearing

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Originally Posted by Lodesman View Post
Deperming isn't done to alter natural magnetic anomalies; it's done to remove induced magnetism from warships, so they will (hopefully) not set off magnetic-influence mines. It involves surrounding the ship with huge electric coils, and turning the ship into a giant electro-magnet. As you can imagine, a destroyer-sized magnet will have a significant local effect on magnetic compasses.
And doing it, is a right pain in the A$$ !!.

So many things don't like being in a big electro-magnet for a few days. - The amount of crap you have to take off when you do this.....

Mark.
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Old 09-06-2018, 08:29   #75
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Re: true vs magnetic bearing

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Correct, and it is important, particularly for cruisers traveling long distances. I no longer recall detail, but it is possible, perhaps even probable, that a compass with inclination set for, say, Perth, Australia, will not work properly, or at all (?) off of Vancouver, British Columbia. The compass makers (or?) have established something like seven zones in the world for inclination settings. It all makes me want to take a nav refresher class, and sail again sans electronic instruments. Doing so would be foolish, but it is a darn good idea to be able to do so.
Your post reminds me of an event that my feeble memory conjured up concerning a sailing vessel called Moonraker, I believe. This occurred several years ago, I think!
She had just crossed the equator and during a dark watch, the navigator, (who was a very experienced fellow as I recall), neglected to adjust his compass card for the difference in declination as they moved from the Northern to Souhern hemisphere and ran the vessel up onto a reef. No one was drowned but the boat was a total loss, as I remember.
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