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Old 17-01-2012, 18:45   #1
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Autopilot Losing It's Way !

We did a recent trip in rather rough weather, the waves were coming from all directions and 35 knot wind coming from starboard side. The autopilot was engaged and it handled well for about 4 hours. Then it completely lost it's way by making more than a 90 degree turn to port.

We disengaged the auto pilot and again re-engaged it a couple of minutes later. It immediately lost it's way - this time turning some 120 degree to starboard. So I hand steer for about an hour or so and then again engaged the auto pilot. It kept course for some 2 hours and started losing it's way again.

What could be the cause of this?

Furuno NavNet vx2 Chartplotter, B&G H2000 Pilot system and B&G Hydraulic Pump and Piston.
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Old 17-01-2012, 18:50   #2
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Quote:
Originally Posted by MooseMoney
We did a recent trip in rather rough weather, the waves were coming from all directions and 35 knot wind coming from starboard side. The autopilot was engaged and it handled well for about 4 hours. Then it completely lost it's way by making more than a 90 degree turn to port.

We disengaged the auto pilot and again re-engaged it a couple of minutes later. It immediately lost it's way - this time turning some 120 degree to starboard. So I hand steer for about an hour or so and then again engaged the auto pilot. It kept course for some 2 hours and started losing it's way again.

What could be the cause of this?

Furuno NavNet vx2 Chartplotter, B&G H2000 Pilot system and B&G Hydraulic Pump and Piston.
You sure that it simply couldn't cope with the yawning of the boat in the conditions.
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Old 17-01-2012, 19:29   #3
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Re: Autopilot losing it's way!

Where's the fluxgate compass sensor and is there a possibility that something with mass was put near it accidentally?
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Old 17-01-2012, 19:29   #4
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Re: Autopilot losing it's way!

Need more information. Did you have it set to steer to a waypoint from the navnet or just to a heading from the fluxgate? Was there any error messages? Did the autopilot clutch disengage when the boat made a gross turn, or was the ram actively steering that direction? Which B&G drive do you have and how old is it? Is there any hydraulic fluid around the drive area? Where is the compass located, and did you make any changes in that area recently? What is stored in the compass area - any metallic objects that could move around in a seaway?

Here is why the info is necessary - error messages will help pinpoint any problem. If the drive clutch was disengaged when the turns happened, it could be a bad solenoid on the drive (happened to our B&G ram). If it was steering to a waypoint when it happened, there could be a communication problem with the navnet. If the drive is the blue Type 1 or Type 2, and is old enough, the brushes could need replacing (happened to our B&G ram). If hydraulic fluid is present around or on the drive, the ram seals could need replacing (happened to our B&G ram). If there has been changes in the area of the compass, any new introduction of something metallic could be interfering. Anything metallic moving around, even the smallest amount, in a seaway could be causing problems (happened to us once with the same symptoms).

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Old 17-01-2012, 20:42   #5
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Re: Autopilot losing it's way!

Thank you for the response!
There are many things I cannot answer as I simply do not know enough about the things you guys are talking about. I will see the boat again in about 6 weeks and will return to this thread hopefully with more answers.

For now;

Quote:
Originally Posted by ActiveCaptain View Post
Where's the fluxgate compass sensor and is there a possibility that something with mass was put near it accidentally?
I have no idea. But what are the implications of this?

Quote:
Originally Posted by colemj View Post
1. Did you have it set to steer to a waypoint from the navnet or just to a heading from the fluxgate? 2. Was there any error messages? 3. Did the autopilot clutch disengage when the boat made a gross turn, or was the ram actively steering that direction? 4. Which B&G drive do you have and how old is it? 5. Is there any hydraulic fluid around the drive area? 6. Where is the compass located, and did you make any changes in that area recently? 7. What is stored in the compass area - any metallic objects that could move around in a seaway?
1. I choose a heading from the B&G Autopilot instrument.
2. No error messages.
3. The autopilot did not disengage - simply actively steering to a very different heading.
4. Not sure which B&G drive we have - 3 years old.
5. No hydraulic ram fluid visible anywhere.
6. The compass SikaFlex seal leaked, compass was removed and refitted with new SikaFlex.
7. Nothing as far as I know - will check on my next visit.
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Old 17-01-2012, 21:00   #6
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Re: Autopilot losing it's way!

If you don't know where the fluxgate sensor is, the first thing to do is find that. It's how your autopilot knows the compass heading and what it uses to maintain direction. A laptop, large metal object, or even a set of silverware put in proximity will cause the effect that you saw.

It's not the only thing that can cause the problem but it's the simplest thing to check and therefore the first.
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Old 17-01-2012, 21:27   #7
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Re: Autopilot losing it's way!

cough windwane cough
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Old 17-01-2012, 23:27   #8
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Re: Autopilot losing it's way!

If the fluxgate compass erroneously perceives that the boat has made a course change, because the compass has been affected by a metallic object, or has moved in relation to the boat, it will try to "correct" back to the course it was steering, often with an abrupt turn.

Note that this is not your main compass. It's a component of the autopilot system.

On my current sailboat the fluxgate compass is not permanently mounted and I set it into its spot when I bring out and deploy the a/p. If the compass is moved even just a couple of inches it throws it off and I get what you described.

On my previous powerboat sometimes the seas would get so bad that the fluxgate compass - which was permanently mounted - was jolted so hard that it again thought the ship had changed course, and so it changed course to "correct."

Usually, disengaging the a/p by putting it into Standby mode, and then reactivating it, will get the fluxgate compass to reset and correct the problem. You said that once you did this and nothing happened, but another time it got you back to normal for a couple of hours until the next problem. This sounds like the fluxgate compass to me. You should check its installation, including choice of location, nearby objects, its stability, etc.

Good luck!
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Old 18-01-2012, 06:03   #9
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Re: Autopilot losing it's way!

Quote:
Originally Posted by rebel heart View Post
cough windwane cough
His boat is a 50' Simonis catamaran. No windvane could possibly steer that boat for many reasons.

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Old 18-01-2012, 06:18   #10
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Re: Autopilot Losing It's Way !

It also might be air in the hydraulic line; try bleeding the hydraulics if you don't find any metal near the ap compass.
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Old 18-01-2012, 06:31   #11
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Re: Autopilot Losing It's Way !

Yeah, air in line that happened to me goind down to Grenada straight from St-Maarten, took us 12 hrs before realizing what was the problem, gosh we realized that we simply adore our auto when going long ways
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Old 18-01-2012, 06:37   #12
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Re: Autopilot Losing It's Way !

I suspect he has the B&G blue T1 or T2 ram, which does not have hydraulic lines. It is a self-contained, all-in-one motor/pump/hydraulic ram unit. It can have air in it, but the bleeding procedure is a bit complicated. It will almost surely leak hydraulic fluid out of the ram arm seal before sucking in air, and that is why I told him to check around and under the drive arm.

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Old 18-01-2012, 06:42   #13
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Re: Autopilot Losing It's Way !

I'm not discounting the possible near object interfering with the fluxgate compass or the possibility of a hydraulic issue, but one of my first checks would be a possible intermittent disconnect of a wire lead at the control box connecting the fluxgate, ram and control head.
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Old 18-01-2012, 07:07   #14
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Re: Autopilot Losing It's Way !

We have a different autopilot than you but had a similar difficulty that proved to be related to the fluxgate. In our case the sensor is located on the main bulkhead under the forward end of the starboard setee in the Salon. On the opposit side of that bulkhead is a hanging locker. It turned out that just before the trip when the problem developed my wife had placed a rack in the locker that allows one to hang a number of garments in a vertical row from a single point. While we normally use only plastic hangers out of concerns about rust stains, in this case my wife had gathered up a handful of wire hangers at home that she hung from the bottom rung of this rack--as it turns out directly behind the flux-gate. When the going got rough, the rack swung back and forth, to and fro, behind the flux-gate and the bundle of wire hangers was evidently enough to goof-up the sensor. I discovered the situation when trying to find a pair of deck-shoes after we finally got to our destination. After removing the offending rack and hangers, the problem was resolved.

FWIW...
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Old 18-01-2012, 10:07   #15
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Re: Autopilot Losing It's Way !

Many thanks for the time and effort writing your responses!
There are many things I will have to check and report back on - hopefully in about 6 weeks.
Thanks!
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