Compass problem

[higgs]

My compass has always been pretty accurate, but on a passage this past week on a SE heading it was suddenly 40 degrees off. Of course I checked for external things that might have been set in the cockpit that would effect it, but there was nothing. Has anyone ever had a compass go out of adjustment?

 

[Stu Jackson]

Where were you? Any local anomalies?

 

[Ross]

parallel wires rather than twisted pairs can pull a compass when they are carrying a dc current. Swing the compass and check the other headings.

 

[Don12364]

40° is HUGE

Fortunately so large as impossible to pass unnoticed and would need a sizeable magnet or hefty current nearby to give this amount of deviation.
IMHO unlikely to be the compass, more likely to be the boat.
Most fluid filled compasses have two magnets suspended below the card and if one fell off the compass would not swing at all. No way could you alter their magetism from outside the compass either.

I saw this once with a compass which had been installed 18" from the alternator - and again when Hunters installed my Hi-Fi cockpit loudspeakers in the steering console!
Anyone added, removed or changed a loudspeaker within 3 feet on your boat?

Presumably we are talking your main steering binnacle and not some electronicy flux gate gimmick compass below decks.

For Info - My autopilot compass is on a locker wall and gets upset if I put a spiral bound book in the locker.

When you find the cause please let us know.

 

[kloudie1]

Did ya see that flight of Avengers that was seen in another post??
Ok.. was it compared to the GPS?? (local current)
Dixie Beer used to come in steel cans..??
Someone on board with a magnetic personality?
Seriously, Higgs, that is a big chunk of "off" is it close again?? or has it remained off??
I agree with Donalex, when ya find it let us know.

 

[higgs]

this was compared to a GPS and it is the binnacle mount compass. i don't know for sure, but I suspected a pro did the initial adjustments because it was accurate. Problem arose on saturday crossing ontario from Toronto. I haven't been out yet since, but more testing is needed.

 

[Ross]

Higgs, I haven't checked but isn't magnetic north about 12 degrees west of true north in your area? 40 degrees would seem to indicate a magnet near by like a magnetic business card or calender or a new chart card of some sort or a flash light with a magnet. Check your wheel for being magnetic.

 

[Winkfish]

but on a passage this past week on a SE heading it was suddenly 40 degrees off.

Was it accurate at the start of your passage and suddenly go off, or was it off at the beginning of your passage?

 

[Warren Milberg]

My guess is that unlless you inadvertently caused this problem by putting or passing something magnetic near your compass, the problem is the GPS not the compass. Comparing a magnetic compass reading to what you see on your GPS may not be a useful thing to do in any event. Not only do the two devices read different things, but at least in this area (Chesapeake Bay), the Local Notice To Mariners often warns boaters of any number of GPS anomalies that can be expected in various areas. The military often run any number of exercises (i.e., ASW) that will also produce GPS anomalies.

 

[wonkodsane]

I'll chime in with Warren to say that GPS resolution in the NCR has been miserable this summer.

 

[higgs]

Good points made. The compass was accurate in these same waters and on the same course (Toronto to Olcott) just earlier this year. The GPS is accurate as the compass course was taking me far east of Olcott. Fortunately, a stack on shore is visible from 20 miles out so I had only gone about 10 miles when i noticed the problem.

 

[kpgraci]

My boat came with (found it in a cabinet) a small pocket compass. I remember thinking this was a good idea as a backup...probably not super accurate but points north nonetheless. In addition to being a backup, you could use one to detect magnetic fields around your main compass.

 

[SoSound]

I have a new glasses case with a magnetic catch which keeps it closed... I also once sent my compass spinning with a screwdriver with a magnetic bit retainer... Did you have a drill driver bit holder in a pocket from some repair or project earlier in the day? How about a favorite screw driver or plyers from your home toolbox that attached itself to the fancy little telescoping-magnetic-parts retreiver (and kept its magnetic properties)?

 

[BobM]

A cell phone can do it too. I had to get out of the habit of putting mine in the cupholder next to the binnacle.

 

[higgs]

Something in my pocket is a possibility.

 

[Paul Brinkley]

Boy Scouts have found that holding a compass too close to their body may get false readings due to pocketknives or other tools in their pockets or on their belts. -Paul

 

[Bob Poff]

Since you're comparing it with the GPS course....
Does the compass read the correct heading just sitting in the slip?
Or compare favorably to another compass?

 

[higgs]

i got out today for the first time since last Saturday when the problem presented itself. I am going to go with something must have been in my pocket - the compass was back to its old, reliable self today on several different headings as compared to the GPS.

Thanks for the help, boys.

 

[Ross]

Hiiggs ,Nancy gave me a magnetic money clip that i am careful to place in the vee berth while we are boating.