Oceanis 485 steering failure

[estarzinger]

Originally Posted by scuba0_1

Why were they unable to stop the wheel from turning. I was able to stop my wheel when it went crazy on a trip with grinding of course but I could hold. it and disengage the ap. What's the case that no one was at the wheel.


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The OP says they were a bit afraid of getting their hand stuck in the wheel so took a moment to figure to move and reach around the wheel to hit the autopilot.

Let's assume #1 that the autopilot failure is the cause rather than the symptom of the water ingress. And #2 that per the op they correctly inserted the emergency tiller and it did not give them steering. That would most likely imply two things (a) that the autopilot had torqued the quadrant and that had sheared off the head of the rudder shaft - which is why the emergency tiller did not give them steering. (b) the shaft was still in the boat, but they had water ingress, so that torquing (and subsequent rudder shaft movement unconstrained by an upper bearing) damaged the rudder bearing seals, which started slowish but steady leaking. This has historically proven a hard leak to stem.

The OP does not say whether they looked inside the compartment at the quadrant/rudder shaft. If they had, this all should have been apparent, and the shaft would have been moving rather vigorously in the lower bearing, as it would have been detached from its upper bearing.

The key question with that scenario is that I would have thought the quadrant would have come loose from the shaft without tearing the head off. That would be the prefered failure mode. It would be interesting to know exactly how the quadrant is attached to this rudder.

I might note that steering with emergency tillers is often quite a bit more difficult than people expect. And that could have been the reason for them saying they were 'unable' to steer with the tiller, rather than damage to the shaft. It would be interested to know if the 'failure to steer' was because it was hard, or because there was no resistance at all. That would tell us quite a bit about the shaft damage.

[Highland Fling]

Originally Posted by estarzinger

The OP says they were a bit afraid of getting their hand stuck in the wheel so took a moment to figure to move and reach around the wheel to hit the autopilot.

Let's assume #1 that the autopilot failure is the cause rather than the symptom of the water ingress. And #2 that per the op they correctly inserted the emergency tiller and it did not give them steering. That would most likely imply two things (a) that the autopilot had torqued the quadrant and that had sheared off the head of the rudder shaft - which is why the emergency tiller did not give them steering. (b) the shaft was still in the boat, but they had water ingress, so that torquing (and subsequent rudder shaft movement unconstrained by an upper bearing) damaged the rudder bearing seals, which started slowish but steady leaking. This has historically proven a hard leak to stem.

The OP does not say whether they looked inside the compartment at the quadrant/rudder shaft. If they had, this all should have been apparent, and the shaft would have been moving rather vigorously in the lower bearing, as it would have been detached from its upper bearing.

The key question with that scenario is that I would have thought the quadrant would have come loose from the shaft without tearing the head off. That would be the prefered failure mode. It would be interesting to know exactly how the quadrant is attached to this rudder.

I might note that steering with emergency tillers is often quite a bit more difficult than people expect. And that could have been the reason for them saying they were 'unable' to steer with the tiller, rather than damage to the shaft. It would be interested to know if the 'failure to steer' was because it was hard, or because there was no resistance at all. That would tell us quite a bit about the shaft damage.

I covered this very scenario in one of my first posts here.

You are assuming here that the quadrant is below the top bearing, that may not be the case.

Like I suggested there may be a seperate autopilot tiller PINNED onto the rudder post, that drilling for the pin and the torque of a full and constant application of a hydralic ram with the quadrant hard against the full travel rudder stop may have been enough force to split the rudder post so that the emergency tiller would not be able to turn the rudder. BUT just MORE guesswork