Autopilot failure rounding South Africa

[Gaia]

Hi all

We are Jim and Helen of the sv GAIA currently trying to get around South Africa. GAIA is a Canadian registered junk rigged sailing yacht of 9 tons and loa of 13m.

She is equipped with a Raymarine St 7001 Autopilot and mechanical type 2 Linear Drive which has served her faithfully for more than twelve years.

The AP works while motoring but now fails when sailing in strong winds when it oversteers by thirty degrees from side to side before quiting with the message 'off course' or/and 'no data. I. E. The AP does not seem able to cope with weather helm. When I replaced the gyro compass it still failed and ditto replacing the course computer with a spare. However both spares were bought used and I cannot swear to their correct functioning as I have never before used them.

We were able to complete the last leg of our passage just recently after laying ahull overnight due to failure of the AP, by motoring directly into the wind and were also able to make a 90 degree course change into the harbour twenty degrees at a time without upsetting the AP.

The Control head properly indicates the rudder position so I assume the course computer knows the rudder position correctly.

I replaced the gyro compass with a spare to no avail. Both compasses indicate a heading that is far out from the course steered while underway by 50 degrees or more. Typically the heading will read say 300 degrees and the course say 240. The readings and their differences will be steady. That has been the case for some time now and appeared not to affect the functioning of the AP. It did appear to be getting worse with time. At the moment along the dock the compass heading corresponds correctly to the magnetic compass.

I have written to Raymarine SA but would appreciate comments from anyone with similar problems and or expertise.

Missing the two crew members we think our Autopilot normally equals (-:

Jim

[ub1]

On my rotary drive raymarine pilot when it starts doing that I check and change the brushes in the electric motor. The box like thing on the end of linear drive. Motor is inside of it. Usually change every 15000 miles or so, depending on severity of weather when used.


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[Snowpetrel]

Just a few random and proably already checked ideas.

Voltage drop on the motor due to slightly corroded wires?

Magnetic junk around the fluxgate compass?

Changes in dip angle due to being further south affecting the compass, and changingbits calibration.

Sounds like you have a neat boat, any photo's?

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[DeepFrz]

My suggestion is that you overhaul the Type 2 drive system motor as well the linear mechanical drive system itself.

[jamhass]

You didn't mention if you use course or wind mode when under sail
Our Raymarine system is very sensitive to the wind instrument data, which is often flaky.
If using wind mode, try course mode.
Just a thought

[Elie]

Maybe the mechanical drive is in trouble?. I had that kind of problem with my hydraulic drive and after purging the oil circuit everything worked like magic.

[Gaia]

Thanks for the interest so far although I am puzzled about the replies suggesting the involvement of the motor. The drive works fine in fact it is the oversteering or over correction that is the cause of concern. It is disturbing to see the wheel keep turning long after it should have and normally did stop! Causing yawing and gybing which when running in 30 kts and big waves is disconcerting! I just cannot see how the motor is the problem. Besides the motor received new brushes and a cleanup after a 'drive stopped' episode while crossing the Indian Ocean two months ago.

And re the mode; we do not have wind mode and operate on the fluxgate compass only. Of interest is that the original course computer is a S3G meaning it has a gyro compass on the PCB to compensate for rolling. The spare course computer bought via the forum, is a S3 model without the gyro compass. Yet with both course computers the AP failed.

Since I wrote I have measured the resistances of both fluxgate compasses and they are within specs.

I also measured the rudder reference transducer resistances and on the anticlockwise stop the resistance is out by 20%instead of the recommended 10%. The other specs are within tolerance. I find it hard to believe that that slight deviation is the cause of the failure.

The final comment was re the response level but operating at higher responses did not prevent the oversteering.

Jim

[Panope]

Originally Posted by Gaia

Hi all

We are Jim and Helen of the sv GAIA currently trying to get around South Africa. GAIA is a Canadian registered junk rigged sailing yacht of 9 tons and loa of 13m.

She is equipped with a Raymarine St 7001 Autopilot and mechanical type 2 Linear Drive which has served her faithfully for more than twelve years.

The AP works while motoring but now fails when sailing in strong winds when it oversteers by thirty degrees from side to side before quiting with the message 'off course' or/and 'no data. I. E. The AP does not seem able to cope with weather helm. When I replaced the gyro compass it still failed and ditto replacing the course computer with a spare. However both spares were bought used and I cannot swear to their correct functioning as I have never before used them.

We were able to complete the last leg of our passage just recently after laying ahull overnight due to failure of the AP, by motoring directly into the wind and were also able to make a 90 degree course change into the harbour twenty degrees at a time without upsetting the AP.

The Control head properly indicates the rudder position so I assume the course computer knows the rudder position correctly.

I replaced the gyro compass with a spare to no avail. Both compasses indicate a heading that is far out from the course steered while underway by 50 degrees or more. Typically the heading will read say 300 degrees and the course say 240. The readings and their differences will be steady. That has been the case for some time now and appeared not to affect the functioning of the AP. It did appear to be getting worse with time. At the moment along the dock the compass heading corresponds correctly to the magnetic compass.

I have written to Raymarine SA but would appreciate comments from anyone with similar problems and or expertise.

Missing the two crew members we think our Autopilot normally equals (-:

Jim

Jim, is your boat made of steel?

Also, are these the highest latitudes that you have been sailing?

Perhaps the weaker magnetic pull of the earth (nearer the pole) is being overpowered by some on-board magnetism (as SnowP mentioned above).

Steve

[lightsloop]

Hi

Our raymarine auto helm refused to hold course while under sail but worked fine while motoring without sails. Root cause was the linear drive. It couldn't generate enough force to steer while sailing, more so one one tack than the other.
If the linear drive is being overwhelmed and the load reduces as the boat yaws, it will again steer back toward course. Until it cannot generate enough force again.
This is the mechanism of the hypothesis that the issue is the drive.
Hope this helps, and good luck!

[Dougtiff]

Look at <pelagicautopilot.com> to replace everything except the type 2 drive, an amazing unit for about 700 buck's, in a small package, i replaced my Robertson AP brain,ect.with this unit, so much better. good luck.

[Emerald Sea]

Jim. At the False Bay YC you will find Rob. He has a Raymarine/electronics shop based at the marina and is very conversant with RM products being an ex-employee and electronic designer for them. He sort out other Raymarine issues for me very successfully. Well recommended.

Unfortunately, I havent his contact details.
Steve
Emerald Sea

[Rigdaddy]

I'm sure you have already checked this, but thought I'd mention it. My quadrant was extremely loose on the shaft, causing the AP to "over steer" according to the rudder position indicator.

[Paul L]

Originally Posted by Dougtiff

Look at <pelagicautopilot.com> to replace everything except the type 2 drive, an amazing unit for about 700 buck's, in a small package, i replaced my Robertson AP brain,ect.with this unit, so much better. good luck.

I've never heard of these guys. That's a pretty good price for what looks like reliable system.

[Littlechay]

Because you have been changing the gyro (fluxgate?) and your heading is "off". Have you done all the calibration routines? Dockside, then the circles etc..?

Where are you in South Africa? I might be able to point you to some contacts in Cape Town. I don't know if there is an actual Raymarine South Africa. I think that MDM are the Ray distributors there. I have head good reports of the Rob mentioned previously.

[Neptune's Gear]

I agree with littlechay. Do the dockside calibration and then the setup at sea. Your gyro should not be off. At all. If the ap does not have accurate heading info, it won't work properly.
Then, check the quadrant for movement on the shaft. Next, from your post above, in your setup the wheel moves with AP engaged. Hold the wheel and try to move it with the ap - simulating rudder resistance. Is the ap power about what you expect? Both ways? Next check that the rudder angle display is consistent throughout the full range of motion, and repeat this multiple times. If it jumps, or is not linear, the rudder angle sensor is the route cause. Try this, report back.