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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > GPS question
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Topic Review (Newest First)
05-30-2004 03:10 AM
NickLindsley
GPS question

Most GPSs have the option to show true heading or Magnetic (this is done automatically as they know where they are). Which way have you set your default?

05-10-2004 04:40 AM
MHRitter
GPS question

You might try downloading the manual and then doing the search for words or combinations of words to disable the compass. The compass decreases battery life by almost 50%. I often us my GPS 12 get the boat headed in the right direction and once that happens I use the old compass to steer and turn off the GPS.

Next Milwuakee GPS Seminar is Jne12th see it at usps.org/lc/door/gps.html
04-22-2004 09:05 AM
wallm
GPS question

For anyone who became interested in this discussion.... I finally got in touch with a knowledgeable person at Garmin. It took several calls and a lot of time on hold. Basically he told me that the electronic compass feature on the Garmin 76S and a couple of other Garmin units are pretty much for walkers but not for sail or aviation use. In other words, one can use the unit to obtain heading over the ground when moving (just like any other GPS) but the compass is not great for obtaining direction steered. In order for the electronic (fluxgate) compass on the Garmin 76S to work well the unit has to be held flat and not be around any metal or magnetic fields, both of which are pretty common in a cockpit. He suggested disarming the electronic compass (which I cannot figure out how to do) or at least changing the factory default setting so that the unit utilizes the GPS to obtain heading at low speeds and not the compass (easy to do and the instructions in the manual are straightforward).
04-19-2004 02:12 PM
Silmaril
GPS question

I would imagine that you may be seeing the effect of a lot of techology in one handheld unit. I think that the electronic compass in the Garmin is more suited to overland "Orienteering" than precise marine navigation.

The price of a good fluxgate comapass for one of the modern integrated navigation/information systems is more than the entire 76S! I have a nice Autohelm/Raytheon hand bearing digital compass that is very accurate but was about $150 or so. Add on all the features of the 76S and, well, they had to scrimp somewhere!

Even my two trusty 7" Danforth Constellations, zeroed to within a degree of each other, move whenever ANY ferrous metal or electronic device comes near them.

Just remember that if you turn off your 76S compass, the resulted calculated heading will be over the ground, which means with a beam current, you may be off 10 - 20deg from your magnetic heading. And if you are not moving, you won''t get any heading reading at all.
04-19-2004 06:03 AM
39512
GPS question

With the boat at the dock, take a magnetic compass reading. Then turn on the GPS and place it near the binnacle. I would guess that the magnetic compass card will deflect.

Turn on the GPS. Stand near something ferrous. See if the heading changes.
04-15-2004 01:39 PM
mdougan
GPS question

Well, obviously, they do it for people who want to use the compass while the the unit is vertical, but they know that it''s not going to be as accurate as your boat''s compass, and at least they say that plainly in their documentation.

I think that the compass itself is just a feature added to make it look better on paper. They even recommend turning it off to help conserve battery life.

Next time you see such a variance, just lay the unit down and you should see it assume a more correct reading.
04-15-2004 11:56 AM
hamiam
GPS question

Call Garmin tech support and ask one of their tech geeks.
04-15-2004 09:08 AM
wallm
GPS question

The night my GPS heading way way off I had the unit upright and it was near a radio. I think both conditions could have thrown it off. However, I like to have the GPS upright so I can see it when I am at the wheel and since I charter different boats who knows about differet magnetic forces in various cockpits. As I mentioned previously, the GPS comes from the factory set so that at speeds <10 mph it uses the electronic compass for heading and at speeds >10 mph it uses the GPS fix from satellites. However, one can change this default so that the unit uses the GPS and not the electronic compass all the way down to 0 mph. I just do not understand GPS units well enough to figure out why they even build in the option, if one would lose accuracy using the GPS as the determinant of heading at slow speeds like 1 or 2 mph, etc.
04-15-2004 03:57 AM
Yodagwb
GPS question

Doesn''t the GPS compass use the change in location to determine the course, therefore any slippage or cross current would factor into your electronic course. Could you of had that kind of deviation from compass course?
04-14-2004 03:10 PM
hamiam
GPS question

not sure if the gps compass is a fluxgate compass like that on an autopilot but I found that I had to move my fluxgate compass away from my boom box as it caused the magnitude of error of which you speak. The speakers in the boom box have magnets which throw off the fluxgate. Same is true for electric motors and any metals, like a knife, that have been magnatized. Just a thought.
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