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Autopilot noise at helm

Discussion in 'Technical Discussion' started by TahoeJohn, Dec 21, 2020.

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  1. TahoeJohn

    TahoeJohn Member

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    Hello,

    The 2001 Horizon 76 I purchased in Florida made it to Ensenada on the big ship just fine and we're now working our way up to San Francisco, currently docked here in beautiful Santa Barbara. Great trip so far.

    One of the first things I need to figure out is why the autopilot, when engaged, is transmitting a significant amount of noise back to the helm. Here's roughly the setup: The helm station (single helm, in the skylounge) has three hydraulic lines that run down, via the ER, to the lazarette and the steering rams, as expected. In the ER, each of the three lines tees over to the autopilot pump. When engaged, the wheel at the helm is disconnected (can spin but has no effect; does not spin by the AP), and the autopilot maintains the heading, as expected. Also in the ER is the reservoir, with the system pressured via a Shrader valve on top.

    What's not expected, and pretty annoying, is the whine being transmitted up to the helm. It's not so loud that you can't talk over it, but it's impossible to ignore. About every second, as the AP makes adjustments, there are whirs and whines of the pump operating.

    I'm assuming that this isn't how it is supposed to work, as I can't imagine someone taking delivery of this boat when new and accepting this. This did show up as a survey item, but no reason offered at the time.

    Any ideas on what may be causing this? Thank you!
  2. rtrafford

    rtrafford Senior Member

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    Sounds like air in the lines as one possibility for noise. Another may be the helm pumps themselves allowing bypass from the pressure provided by the pilot pump. Is this a Hynautic steering system? Not sure that I understand the setup given that your helm reportedly disengages when the pilot has the helm? A purely mechanical hydraulic system would still allow the helm to push fluid.
  3. Pascal

    Pascal Senior Member

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    Had the same issue on a 2003 johnson 70 skylounge with single station power steering hynautic You could a slight whine although it wasn’t loud enough to be a bother. Never looked into
  4. TahoeJohn

    TahoeJohn Member

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    Thank you for the thoughts and ideas. Yes, Hynautic. I, too, am puzzled by the helm disengaging. It seems like there would have to be some type of solenoid to do that bypass/disconnect. I need to dig around through the ER a bit more and fully understand the plumbing of this system. The pump and tees (and maybe more) are somewhat buried in front of the port fuel tank and behind a bunch of other stuff, so I'll need to wedge in there once the engines are cooled and describe the system more completely.
  5. rtrafford

    rtrafford Senior Member

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    Ok, whine, I think I missed that. That's the sound of hydraulic fluid being moved through restrictions. Look for check valves while researching. Once familiar, energize the system at the dock and revisit your tour. Listen and find the culprit. Reasonable chance you'll find a weak link. Mine, it was the helm pumps themselves. They were tired, and the working of the fluids with pilot turns was managing to actually pull air in from the tank. That air made knocking sounds that were obvious and apparent within the helm pumps. I rebuilt those with new seals and bearings. Once cleaned up the issue was gone. The pilot even became faster to respond and worked better in holding a steady course.
  6. rtrafford

    rtrafford Senior Member

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    The pilot pump, when operating, does it start and stop? Likely given the persistent whine it runs continuously. To do this it must allow fluid to return to a volume tank from which it also pulls. I would think an intermittent pump wouldn't whine.
  7. d_meister

    d_meister Senior Member

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    Are there any flexible hoses in the steering plumbing? That helps to break the sound transmission path. Also, have a closer look under the helm and be sure that the AP installer didn't add a small reversing pump to answer the AP helm commands. I've seen that where the correct application would be solenoid valves on a power assist Hynautic system.
  8. Capt Ralph

    Capt Ralph Senior Member

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    I was thinking vibration transmission also.
    A+
    pics 5 20 04 001.jpg
  9. rtrafford

    rtrafford Senior Member

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    We actually had blow-by with the internal workings of one of the helm pumps. Rebuilt, all noise cured. Although mine wasn't a whine.

    Attached Files:

  10. TahoeJohn

    TahoeJohn Member

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    Thanks again for all your thoughts on this. I'll need to confirm that the pump is starting and stopping but it definitely sounds like it is. The pattern is: whine for half a second to 5 seconds, silence for a half a second to a second, whine again, silence again... The whines are all different pitches, as if the motor sometimes turns slowly (lower pitch) and sometimes faster and more urgently (higher pitch).

    I agree that it's sound being transmitted up to the helm via the hydraulic lines. The question is why and how to stop it. That's what I'll be trying to map out.
  11. MBevins

    MBevins Senior Member

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    It really sounds like the pump noise is telegraphing up the hydraulic lines. What's interesting is that you say the pump is in the lazarette? Or ER? Viking put mine under the helm station so I hear it working, but only when in heavy seas. I'm wondering if you have air in the line? What's the pressure showing at the Schraeder valve? If low then air is probably the noise.
  12. Pascal

    Pascal Senior Member

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    Using flex lines between the pump and the hard lines, and maybe between the hard lines and the helm maybe something worth trying
  13. T.T.

    T.T. Senior Member

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    Bingo! If the wrong fluid has been added, the double pilot check valves will corrode and eventually restrict fluid movement, then seize. Have someone who knows the ins and outs specifically for Hynautic look at the system.
  14. rtrafford

    rtrafford Senior Member

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    So it's now obvious that you have a bidirectional pilot steering pump. That pump is injecting hydraulic pressure on one side of the system every time it engages. Then it will stop and direct pressure to the opposite line to correct the rudder angle. You're whining every time it's energized. Either it's a noisy or failing pump that is transmitting that noise with every push, or you have worn seals at your helm pump that are allowing some blow-by when one of the sides is pushed by the pump.

    Is the noise loudest at your pump or at your helm? Follow the noise...
  15. TahoeJohn

    TahoeJohn Member

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    Yes, makes complete sense. I'll see what I can hear down by the pump with the engines off (once this trip is over), and probably rebuild the helm pump, regardless. It's not terribly responsive and I wouldn't be surprised if it hasn't seen any maintenance on it since new (19 years).

    Thank you again! Having a plan of action helps maintain our sanity amidst 10 hours of non-stop whining every day. :)
  16. rtrafford

    rtrafford Senior Member

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    Easy trick, while you're running now, grab a piece of hose, tubing, snorkel, whatever, and use it between your ear and the steering helm to focus the sounds coming from that unit while you run. You can do the same at the pilot pump if accessible, amidst the louder noises, to help identify the source.

    But most of all, enjoy the trip.
  17. TahoeJohn

    TahoeJohn Member

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    We made it into San Francisco Bay just before Christmas and have been relaxing in our new slip here since.

    Today I mapped out the Hynautic steering system. There's power assist from a pump on the port main engine, with three cylinders in the lazarette to effect the steering, plus a reservoir, a water-cooled heat exchanger, inline filter, and miscellaneous fittings and blocks to connect everything together.

    The connection between the helm and the pump itself is very straight-forward, however: There are three copper lines that come down from the helm to the engine room, labeled P, R, and S (I assume Port, Return, and Starboard). The AP motor is teed off these three lines, just as a 2nd helm station would be plumbed. No external check valves, solenoids, etc. The whining sound appears to come equally from the AP motor as it does from the helm itself. (Since copper pipe and hydraulic fluid transmit sound so efficiently, this makes sense to me.)

    The air pressure on the system was very low, down around 15 PSI, with 45-50 PSI being recommended. As some have suggested, there could very-well be air in the system which needs to be bled.

    Given all this, here's my planned course of action:
    1) Send the Hynautic H-21 helm pump to Seatech in San Diego for a rebuild, just $180 with a 2 day turnaround. Whether it needs it or not, this feels like a good thing to do.
    2) Fix a couple of minor leaks that I've found, change the fluid, pressurize correctly, and bleed the system.
    3) If the noise persists, replace / rebuild the AP motor. (I do have a spare that came with the boat.)

    Thanks again to all for the help so far and please let me know if I'm missing something.
  18. Capt Ralph

    Capt Ralph Senior Member

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    IMO, if you can steer the boat at either helm and it has a good feel, and your pilot drives a straight line, then your course of action is a waist of time.
    You never confirmed if you had flexible (hose) connects at the help pumps.
    Now that you mentioned a power assist system, I'd start by replacing the filter. Listening to the assist pump on the engine or chattering in the control cylinder or rudder post.
  19. TahoeJohn

    TahoeJohn Member

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    Sorry, there are no flexible connections between the helm pump and the AP drive pump; hard copper lines all the way from both back to the lazarette, where one of the cylinders appears to be under direct control from whatever's steering with the other two cylinders kicking in additional power from the engine-driven pump.

    This loud whining does not seem to be normal, and I'd really like to solve the issue. Things do function correctly, but with an excess of noise. I'll add changing the filter to my course of action. Thanks...
  20. rtrafford

    rtrafford Senior Member

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    Yes, with pressure low and perhaps compromised fluid or filter, there is a good chance of air being introduced. You might feel what seems like sponginess with the helm hard over. Rebuilding the helm pump and purging, flushing the system with new fluid and filter is a terrific no-nonsense first step. Chase all old fluids with new, all the way to the cylinder. Watch for any signs of dirt or rust. Black may be a sign of wear from the various seals.