Rudder Hydraulic Lock Symptoms?

Hi Fellow Trawlers,

In getting to know our Nordic 39 autopilot (Furuno Navnet3d electronics), I managed to tell it to start at the wrong poing at which time the autopilot moved the rudder full starboard. At which point I disengaged the autopilot and found that the wheel would not immediately move the rudder off starboard. I moved the wheel a couple revolutions to port to no affect. I checked the rudder mechanism visually and yes, it was up against the stops. The wheel would move to port or starboard with maybe twice the normal force and also felt rubbery. My 1st Mate was frightended because I said "Oh S***" and she says I never say that. So I powered down all the electroncis, cycled the breakers for electronics and especially including the autopilot breaker. Still no joy on the turning wheel with all electronics off. After turning electronics on and leaving autopilot off, no change, still stuck hard on starboard. Well, after 15 minutes of trying the wheel and thinking about the problem, the wheel was able to move off the "locked" position. I had changed nothing; the problem seemed to resolve itself.

So what do you think? Has anyone encountered anything like this? My suspicion is that a) the rudder hydraulics had encountered a hydraulic lock, and b) the rubbery feel when locked suggests either a soft hose or air in the system. Perhaps a check valve problem?

Belatedly, I've wondered what would have happened if I had entered a course that would have made the autopilot steer to port.

Thanks for reading and I look forward to hearing of your suggestions.

Dave
P.S. the boat is 12 years old and the autopilot works fine when I give it a proper course.

I cannot answer that one, Dave, but your tale caused me to recall part of the setup for my old Furuno AP. While going through the prompts of the initial setup, the operator is asked to turn the wheel to the maximum left and right positions the AP will be allowed to turn the wheel. I stopped well short of the hard over position because I do not believe an AP should ever have to use more than half the available rudder swing.

Does the steering system have one of these, located right near the ram? I'm 99% sure it does, and there is no other component that can cause your issue. It controls the expelled fluid from the ram, directing it to the return line back to the helm. Without it the ram cannot move. It got stuck on the hard over pressure, eventually freed up. It would have happened also if you had forced the rudder with the helm. Jiggling the wheel back and forth will usually free it when stuck. First thing would be to flush the whole system with new fluid and insure it is bled, then test with the helm. If it still malfunctions you will have to take it to a hydraulic shop and they should be able to fix it. These haven't been available for decades, but as of a few years ago a service kit was still available.

When this happens, is your helm at full starboard (or full port) does it feel like it looses its "grip"? i.e. the helm turns without feeling any resistance. It essentially stops pumping hydraulic fluid through the system?

If YES, you probably have AIR in the hydraulic line that needs to be bled out. If this happens more than once or twice you probably have a leak in the hydraulic system.

Let me know if these are your symptoms and I can tell you how I bleed my air bubbles out. ((A new ram / cylinder at my rudder post is planned for this winter.))

I had a similar situation, except worse. If you don’t set your limits correctly it can actually apply enough pressure to push your ram out of the seals and get stuck. In my case the AP was set up correctly, but the attachment to the rudder had broken and the autopilot didn’t know to stop pumping, so it pushed the ram beyond limits. The ram had to be taken apart to get it back in… I tried forcing it a little and decided better to rebuild ram while at it.

With a center mark on steering bar do dock side set up with a second person watching to ensure you stop before or right as you hit the stops… also measure the distance to your stops, if you have a 9” ram the distance shouldn’t be more than 9”.

With all the geometry going on, length of rudder, where steering attachment is, where ram is located, etc, you may need to adjust your stops.

Good luck!

Steel N Time said:

I had a similar situation, except worse. If you don’t set your limits correctly it can actually apply enough pressure to push your ram out of the seals and get stuck. In my case the AP was set up correctly, but the attachment to the rudder had broken and the autopilot didn’t know to stop pumping, so it pushed the ram beyond limits. The ram had to be taken apart to get it back in… I tried forcing it a little and decided better to rebuild ram while at it.

With a center mark on steering bar do dock side set up with a second person watching to ensure you stop before or right as you hit the stops… also measure the distance to your stops, if you have a 9” ram the distance shouldn’t be more than 9”.

With all the geometry going on, length of rudder, where steering attachment is, where ram is located, etc, you may need to adjust your stops.

Good luck!

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To expand on this excellent point, autopilots may have different dockside setups. In my Furuno's case, when setting the left and right rudder limits, the program runs the ram to the limits and asks if this is correct. I was able to manually return the rudder back toward amidships by 5 or more degrees before punching the OK button because I can see no need for an AP to ever have to use hard over rudder.

EngNate said:

Does the steering system have one of these, located right near the ram? I'm 99% sure it does, and there is no other component that can cause your issue. It controls the expelled fluid from the ram, directing it to the return line back to the helm. Without it the ram cannot move. It got stuck on the hard over pressure, eventually freed up. It would have happened also if you had forced the rudder with the helm. Jiggling the wheel back and forth will usually free it when stuck. First thing would be to flush the whole system with new fluid and insure it is bled, then test with the helm. If it still malfunctions you will have to take it to a hydraulic shop and they should be able to fix it. These haven't been available for decades, but as of a few years ago a service kit was still available.
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Teleflex stopped making the Univalve in 1987. I doubt there is one on a 12 year old Nordic. Most of the newer pumps have check valves built in. They also have a needle valve. On mine I can isolate the autopilot pump from the manual pump (helm pump) by closing the needle valves.

I'll propose a different theory. The steering pump has check valves that pop off when you turn that direction, but close otherwise. If it didn't, the rudder would not stay where you put it. The autopilot pump runs in parallel with the steering pump and is a reversing gear pump. If it put full pressure into one side of the cylinder and bottomed it out, there might be high static pressure in that side of the circuit, too high for the steering pump to overcome. After some time the leakage (there is always leakage in a hydraulic system) reduced the pressure enough that things returned to normal. I've no idea if that is what happened. But it seems like it could, given the circumstances (autopilot hard over suddenly). Would not happen if the soft stops in the autopilot computer were correctly set. I agree with the above post that you'd really want the software stops set short of the hard stops, no reason to stress things like that.