Too close?

[oscarvan]

Somewhere buried in another thread Mr Clarkson mentioned a magnet/whacky compass situation which was an "aha" moment for me.... The PO's choice for compass sensor and Algae-X

So is this too close?

 

[SKYCHENEY]

Try a hand held compass and move it around the area and see if/how much it's affected.

 

[oscarvan]

Try a hand held compass and move it around the area and see if/how much it's affected.

Simple yet elegant and scientifically sound..... why couldn't I think oft that.

And the answer is...... Nope. The magnet has a serious effect on the handheld compass up to about a foot away. Down by the hull it's nothing.

 

[Captain Ralph]

Is that the AP compass in the bottom of the pic?

 

[racclarkson@gmail.com]

Simple yet elegant and scientifically sound..... why couldn't I think oft that.And the answer is...... Nope. The magnet has a serious effect on the handheld compass up to about a foot away. Down by the hull it's nothing.

You might have to de-power the boat other than AP and plotter. Then you can energize circuits and look for a swing. Or maybe the compass is just too close to the iron. In that case, detaching it and moving it even a few inches will produce change.

 

[rsmith]

Is that the AP compass in the bottom of the pic?

Looks like the depth transducer to me.

 

[oscarvan]

Looks like the depth transducer to me.

That is an excellent comment..DUH on me..... So now I'm Google image searching Garmin depth transducers and autopilot compasses and it appears you are right. Which means I haven't found the compass yet...... It was the "BOW" marking that sent me down the wrong path..... So do I have something "forward looking" here to map the bottom? I know OF that but have never really delved in to it......

 

[doc g]

Have you run the boat to see if its a problem??? If the AP performs properly why mess with it ??.............

 

[oscarvan]

Have you run the boat to see if its a problem??? If the AP performs properly why mess with it ??.............

Oh no, there is a problem. On certain headings the compass is 30º off, and with the bow aimed in the right direction telling the autopilot to navigate to a point ahead will result in an immediate turn. Eventually it will figure the drift and start correcting for what it probably thinks is a hellacious cross wind/current but that's no way to operate.

Way I'm currently working it is to aim the boat in the right direction and hit "heading hold and ignore the number. Make small changes to stay on the line. COG is, of course, in the ball park.

It works and I get there just fine, heck when I was a kid all we had was a whiskey compass uphill both ways........

 

[Play'N Hooky Too]

It sounds like you may need to re-calibrate your AP. There is a procedure in the manual for do this.

Mine is currently the same way. Depending on the direction I'm traveling, the AP can be off by up to 15 degrees from my compass heading and/or the COG heading on on my plotter. I've just been compensating by monitoring my track on the chartplotter and tweaking the heading adjustment on the AP as necessary to keep me on course.

Recalibrating the AP has been one of those round-tuit things on my list for a while now.

 

[doc g]

Navigate to a waypoint instead of a compass heading. ........Pat

 

[Captain Ralph]

The later flux-gate compasses can be calibrated. A special program helps them make a real 360 degree swing. Check your owners manual.
I remember working on older APs like Benmar, a real compass with spokes in the card that an optical eye would read. No calibration on these beast.
Other mfg's used this style and some are still in service.

I have also chased later compass issues when mounted close to bilge, sump and black water pumps.
I remember an engine alternator driving one compass crazy at different speeds.

The best horror story; compass installed in the bottom of a state room closet. All was good till suddenly one weekend the AP went crazy; Found steel toed shoes in there also.

What model AP do you have?
Find the compass and survey the area well. Could be a tool box close by.

 

[SeaEric]

Did I miss the comment that says what brand the A/P is? If it's a Garmin, I own one and have some related experience.

 

[oscarvan]

Yep, late model Garmin.

 

[bigbill]

is the garmin networked with other stuff through a nmea 2000 backbone? mine had similar problems until i put a terminator plug on the backbone. check to see if you have a terminator

 

[SeaEric]

The compass for the Garmin AP that I have is about the size of a tennis ball. We had all sorts of trial and error before we found a good location which ended up being low in the port side hanging locker in the aft stateroom. We tried various locations as suggested by the Garmin install instructions. At one point we thought we had it, but while underway it would unexpectedly veer off - often when I was doing an engineroom check. it turned out that the 12v DC lighting had a major effect on the compass. Turning the DC engineroom lights on caused mayhem. The small hand held compass was a big help in the search. One more thing: When I purchased the AP Garmin said that the "Rudder Feedback Sensor" was optional. It's not. Without it we couldn't get the unit to work properly. With it added (plug and play) no problem. it also adds the rudder angle indicator to the Garmin display, which is nice to have.

 

[racclarkson@gmail.com]

Exactly. Go back to Post #5. It can be the most insignificant combination that causes the swing. And your description is exactly in line with my experience aboard Aslan.

 

[oscarvan]

Thanks all for the excellent suggestions. I will now find the tennis ball and follow the suggestion in post #5.

 

[Boatsb]

Which model garmin?

The "tennis ball" is older technology. The last 2 or 3 models don't use it.

 

[wallison]

When installing the Clear Cruise system I used a magnetometer iPhone app called iNstall from Gemeco. The app (recommended by Raymarine) is free, worked like a charm and will tell you how much RMI there is, and whether it’s a problem.