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Old 31-05-2010, 02:14   #1
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Fluxgate Compass Question

Our boat has got an oldish but generally satisfactory electronics suite -- Raymarine RL70RC+ and RL80CRC+ displays/charplotters, 4kW Pathfinder radar. It doesn't do AIS and the cockpit display is monochrome, but I think it will do fine for a couple years. If you upgrade your electronics every time a new generation comes out, you will be broke very quickly, I say.

When we bought the boat last year everything worked fine. But this year all of sudden the system can't figure out the boat's heading, and the radar started working intermittantly . Sometime the heading is shown correctly; sometimes it's off by 90 degrees or more.

The autopilot continues to work fine (and I don't understand how it can, but it does) but the radar won't do its MARPA thing.

I have searched and searched for the obvious thing -- some metal near the fluxgate compass, which is mounted under the saloon sofa. Nothing.

Next thing I'm going to try is the connections to the fluxgate compass -- look for a bad ground or bad wire connection.

Any other thing I should look for?

Do these things typically go bad, requiring replacement?

And if I do end up having to replace it, any tips on which unit to choose?

Thanks as always for your words of wisdom.

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Old 31-05-2010, 04:13   #2
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Boat: C&C 34
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I assume that all of the stuff is Raymarine or Raytheon stuff.

If so they probably use the original seatalk for communications between the units. The autopilot probably is OK since the fluxgate is attached to it directly. The autopilot then feeds the heading information to the rest of the instruments thru seatalk. It might be OK again if you just remove the seatalk cables and plug them in again (refresh the connection), you might have to power the bus also. Many installers do not do this and it catches up with you over time. An underpowered seatalk bus can cause all kinds of weird problems especially if the wire run is long.

The back of instrument manual will tell you how to power the seatalk bus, its not hard to do.

Good luck.

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Old 31-05-2010, 04:30   #3
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We had a similar problem two years ago - the autopilot showed a heading 120 degrees off from the mag compass, but still would steer the course even though off. I checked everything. Finally had a Raymarine installer check it out, he unmounted the fluxgate, but kept everything turned on, then turned the fluxgate as if the boat were turning. The compass heading on the autopilot appeared as if the boat were turning. He went both directions. Finally said fluxgate was okay. He bench tested the course computer ok. Lastly, he checked the gyro unit and said it was bad. I got a new autogyro and courses are correct. We have an older 7000 autopilot and Model 300 course computer. But the autogyros work with the older instruments/computers.
Bottom line, it might not be your fluxgate compass. Try testing all the instruments.
S/Y Vingilot
lying Marmaris/Turkey

Life isn't a journey to the grave with the intention of arriving safely in a well preserved body, but rather to skid in broadside, thoroughly used up, worn out, proclaiming, "Wow, what a ride!"
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Old 31-05-2010, 05:58   #4
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Thanks! That's interesting information. So Gegrove -- you have the separate gyro compensator and fluxgate? Not the Smart Heading Sensor?
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