Can't find the %$#@! Compass

[Chuck Hawley]

I am currently chartering a Moorings 4600 cat in Croatia, and the flux gate compass appears to be affected by some new metal influence. The problem is that I don't know where the flux gate sensor is, so I can't figure out the solution.

I tried changing the calibration for rotation, but it only solved the problem on a single heading (thus, I realize I need to swing the compass). This problem came on after a week of blissfully accurate autopilot operation, so SOMETHING has changed in this catamaran between Week 1 and Week 2. It's as if someone stored a speaker in their stateroom and didn't realize that the compass sensor was behind the bulkhead.

The 4600 is made by Robertson Caine, and this model is about 3-4 years old. The autopilot is from Raymarine/Autohelm and it's an ST6002 control head.

Thanks in advance,

Chuck Hawley

[Paul Elliott]

Check any recent provisioning stowage. I have a locker with a fluxgate on the other side of the locker wall. It's plainly marked "Compass Area- No Metal" or something like that, but we managed to store a bunch of canned food there anyway. I spent a day trying to figure out why my autopilot calibration was so far off. When I discovered and relocated the cans it all went back to normal.

[belizesailor]

Ask Moorings base?

[JohnT]

The fluxgate used to be located in the cupboard in the galley - as you enter thru the sliding door from the cockpit, it is just under the counter top to your right, but accessed from the working area of the galley side. On some of the later boats they were moved to behind the panel around the mast step (behind the round R&C logo).

[Chuck Hawley]

Originally Posted by JohnT

The fluxgate used to be located in the cupboard in the galley - as you enter thru the sliding door from the cockpit, it is just under the counter top to your right, but accessed from the working area of the galley side. On some of the later boats they were moved to behind the panel around the mast step (behind the round R&C logo).

Ding, ding, ding, ding!

You win the award! Exactly where you predicted (under the counter, mounted where we stow the plates and dishes).

However, there's no metal in the area so my diagnosis is still suspect.

Here are some additional clues:

1. Worked for a number of days (held a course, agreed with steering compass)
2. Started to have lots of deviation from steering compass, but would still hold a course.
3. Caused C90 Raymarine display to be mis-aligned with the chart; the boat symbol appeared to be going sideways.
4. Originally tried to set the "rotation error" as if the compass was not aligned with the center of the vessel.
5. That worked on one heading, but rapidly failed on other headings.
6. Tried to swing the flux gate by spinning circles, but the course computer never said "OK".
7. Now if you engage the compass, the compass display starts counting up as if the boat is turning. Does not hold a course.

I could really use an autopilot. Any ideas?

Chuck

[hellosailor]

Shot in the dark:
You've confirmed the sensor is in the clear. That leaves you:
1-Internal sensor failure, nothing you can do about that.
2-Internal control board (main board) failure, nothing you can do about that.
3-Possibly something running alongside the sensor leads to the system, causing a stray induced voltage that "pushes" the system over in one direction.

You'd need hands and eyes on the wiring to the sensor to see if anything is running near it. Anything that has to be near it should be shielded, or twisted pairs, or crossing at right angles.

Other than checking for that, I think all you can do is call the maker and say "Has anyone on this planet ever have this problem before?" and see if they're familiar with it.

[JohnT]

Chuck, do not always look inside the cupboard for metal - what is on top of the counter top? I once had a crew member who threw his camera pouch onto the counter and the autopilot went nuts. The pouch had the smallest of magnets to keep the flap closed, which affected the autopilot and did things as you describe. If a you find nothing, the fluxgate could be faulty and need replacing. They do break sometimes! Contact the charter base and have them send out a tech dude. I doubt a factory reset of the MFD would solve the problem. John.