Compass and GPS Headings

sasto

Captain
Joined
Jun 1, 2010
Messages
3,918
This may apply to some but may also be interesting to others. I'm blaming getting lost on my compass..

Magnetic north, the point at the top of the Earth that determines compass headings, is shifting its position at a rate of about 40 miles per year. In geologic terms, it's racing from the Arctic Ocean near Canada toward Russia.

As a result, everyone who uses a compass, even as a backup to modern GPS navigation systems, needs to be aware of the shift, make adjustments or obtain updated charts to ensure they get where they intend to go, authorities say. That includes pilots, boaters and even hikers.

"You could end up a few miles off or a couple hundred miles off, depending how far you're going," said Matthew Brock, a technician with Lauderdale Speedometer and Compass, a Fort Lauderdale company that repairs compasses.

Although the magnetic shift has little impact on the average person and presents no danger to the Earth overall, it is costing the aviation and marine industries millions of dollars to upgrade navigational systems and charts.

Because GPS navigation draws on satellites, it has no reliance on magnetic north. On the other hand, satellites and GPS systems can malfunction. For that reason, Tom Cartier recommends all pilots and boaters keep a compass handy as backup.

"The magnetic compass is what gets you home in your boat or plane when everything else quits," said Cartier, a senior deck instructor at Maritime Professional Training in Fort Lauderdale. "It's a very, very valuable piece of equipment."

Cartier said large ships and planes have sophisticated electronic navigation systems, but the vast majority of small boats and planes have magnetic compasses and rely on them heavily.

"They don't have the money to spend for a sophisticated system," he said.

He added that boaters should always bring updated maps, showing the latest corrections for the magnetic north shift, even if they have GPS
 

Mohawkmtrs

Chief Petty Officer
Joined
Jan 13, 2010
Messages
563
Re: Compass and GPS Headings

If your GPS is set up to reference "True North", don't forget to "correct" the compass with regard to Variation and Deviation.
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Re: Compass and GPS Headings

So, what's new about that? If you have ever taken a CG Aux course--even a beginners course-- you know that it shifts yearly. That's why new charts are published every year. The only constants that you can rely on are death and taxes--and I aint so sure about death. It is quite possible that (in the future) they will keep you alive longer just to squeeze you for more taxes
 

JoLin

Vice Admiral
Joined
Aug 18, 2007
Messages
5,146
Re: Compass and GPS Headings

The chart's legend tells you the year it was published, the variation from true north in the year it was published, and the yearly change in variation from that year forward.

Honestly, unless you're travelling awfully long distances, that annual change takes a long, long time to make any practical difference in a point-to-point heading. What with the yawing and bouncing of boat, which causes the compass rose to gyrate as well, I defy any of you to steer a completely accurate magnetic course over any significant distance anyway.

Oh- and how many have calculated the deviation of their particular compass in their particular boat, over several headings, and keep a 'correction table' taped near the compass. LOL.

My .02
 

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
8,234
Re: Compass and GPS Headings

Old news! When I used a Loran I would call the USCG annually to get an update on the new coordinates to input into the setup. Now, if you use a GPS, just be sure to renew your waypoints every year and you'll be fine.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,581
Re: Compass and GPS Headings

The amount of error cause by the magnetic shift is miniscule unless you are travelling thousands of miles. Even with that, the affect of tidal action introduces even more error.

The change in magnetic north obviously doesn't affect navigating by GPS at all. If you use your compass to make your heading described by the GPS, you may have more of an arc to your travel(again miniscule) instead of a straight line, but it won't affect getting to your destination.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,581
Re: Compass and GPS Headings

If your GPS is set up to reference "True North", don't forget to "correct" the compass with regard to Variation and Deviation.
Why would anyone set up their GPS to point to True North?
 

NYBo

Admiral
Joined
Oct 23, 2008
Messages
7,107
Re: Compass and GPS Headings

The farther you are from the magnetic pole, the smaller the effect. Simple geometry.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
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May 19, 2001
Messages
26,064
Re: Compass and GPS Headings

The farther you are from the magnetic pole, the smaller the effect. Simple geometry.

Isn't that exactly the opposite since the closer to the equator the larger the deviation?? I understand the latitude's would be easier to determine due to the spacing however, wouldn't North be further off for a L O N G voyage? Oh carp now I am confused :facepalm:
 

Fireman431

Rear Admiral
Joined
Sep 17, 2007
Messages
4,292
Re: Compass and GPS Headings

Maybe that's why so many of the boats never leave their marina...:rolleyes:
 
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