Strange Hydraulic Steering Issue

[GoldenDawn]

On my KK42, I have a two-station hydraulic steering system with an autopilot pump plumbed into the system near the steering ram. Last week when we were out I noticed a gentle 4 sec roll - initially thought it was a ferry wake and then realized it was the autopilot (ComNav). My first trouble-shoot was adjusting the autopilot controls - loosening and tightening course tolerances and adjust speed of correction. No difference.

We noted some asymmetry in hand steering - turns more easily to port than starboard and also that the first turn of the wheel is easy but second turn meets quite a bit of resistance. I thought this might be triggering the autopilot to be more responsive in one direction than the other and cause the roll.

We disengaged the hydraulic system from the rudder and hand steered. There is no asymmetry in the rudder hand steering so it is not big rope or log on the rudder.

Steering fluid is full and it does not feel like air in the system. No pools of fluid lying around.

So here I am, welcoming ideas

 

[GregBrannon]

You mention a roll, but is the heading wandering back and forth? If so, how many degrees from the set course?

 

[GoldenDawn]

You mention a roll, but is the heading wandering back and forth? If so, how many degrees from the set course?

Heading change is <5 deg each side - but just enough to set her to a gentle roll. I think that is her natural frequency (4-5 sec).

I wondered if the pump could be more forceful one way that the other. The auto pilot steering pump is 18 years old.

 

[Bud]

Maybe one of your solenoid valves is not closing all the way letting hyd fluid by.
Bud

 

[Northern Spy]

Sounds like speed control, or feedback rod assembly issue. I've inadvertently "adjusted" my speed control on my ComNav by impatient button pushing, instead of getting out the manual. I've also had a bent feed back rod from one of my kids tossing a fender in the lazerette. Could be a deadband issue too. Check to see if you can tighten it up at zero rudder angle. I suppose it could be a sloppy ram to rudder bushing, or some other mechanical looseness. Just thinking out loud.

 

[klee wyck]

Could be the ram. Even if the rod and external surface are dry suggesting the rod seal and wiper seal are ok, you could have lost the piston seal putting fluid on the back side and building pressure there?

 

[twistedtree]

If manual steering isn’t right, then the problem is in the steering, not the auto pilot.

Perhaps you can have someone watch and call out actual rudder movement while you operate the wheel? Or put a GoPro pointing at the rudder gear and monitor on a phone or tablet while you operate the wheel?

And does it behave the same from both helms?

Can you valve off the AP pump?

There are check valves in the helm and AP pumps so when one pushes fluid to steer, it doesn’t just flow back through the other pumps. One of those might be sticking.

Or you have a bunch of air in the system, but then the question is how did it get in?