Wednesday, September 09, 2009

Steering mechanism

In response to an anonymous comment yesterday, I thought I'd explain how Lady Jane's steering mechanism works.

Please bear in mind that I'm no expert, so this is simply my understanding....

First off, the 'lump' in the middle with the wires from it, and connected to the arm, which is in turn connected to the rudder post, is the rudder position indicator sender. At a guess, this sender is a variable resistor which probably operates between 0 and 24V. This in turn is shown as the rudder position in the wheelhouse, with the midships position likely at 12V on what is probably essentially a moving coil volt meter. Hard port would be say 24V, while hard starboard would likely be 0V.

I do not doubt it is very handy for a skipper to be able to see instantly where the rudder is positioned, regardless of the steering mechanism involved.

Now Lady Jane has three separate mechanisms for steering, which are all achieved by moving the rudder via the rudder post you can see right in the foreground of yesterdays picture.

The crudest, and simplest, mechanism is steering using a lever which will go over the post there. I have the lever, and key, floating about on board somewhere. (Makes mental note to get this together and stowed safely).

I've not tried to use the lever, but suspect it would take two people with ropes and pulleys to actually move the rudder with any semblance of control over Lady Jane. Oh yes, and a lot of shouting and cussing from the wheelhouse!

The second, and currently most used, method of steering Lady Jane is by using the manual hydraulic pump directly connected to the wheel in the wheelhouse. The pump in the wheelhouse holds a reservoir of hydraulic oil which is pumped through port or starboard steering pipes down through to the rams which in turn push the rudder. You can just see the pipes entering the steering room from the deck to the left there.

The way hydraulics work is a force on a small diameter piston over a long distance (the wheel) causes a proportionally larger force on a larger diameter piston over a short distance (the rudder).

Turning Lady Jane using the manual pump takes plenty of turns of the wheel from full port to full starboard. I forget how many, but it's loads.

The final method of steering Lady Jane is electrically, using the hydraulic power.

The hydraulic power is provided by a 110V DC motor, which drives the hydraulic pump. This unit, and it's reservoir, is visible right at the back of the steering room there.

The two hydraulic systems are totally independent of each other, so using the autopilot does not move the wheel. I presume there are some one way valves in the piping somewhere which makes this possible, though I don't know where.

Currently, to operate the steering, there are two buttons in the wheelhouse, red and green unsurprisingly, which turn Lady Jane to port or starboard. These buttons operate the 110V DC hydraulic solenoids, one of which is visible to the right of all the hydraulic pumping gear you can see at the back there. I've taken the left hand solenoid off, as part of fixing one of the leaks I have in the system.

The solenoids can also be driven by Lady Jane's autopilot, but this system, although still connected, is defunct as it's compass etc. was robbed off of the boat at some point in the past. I had been toying with the idea of developing my own auto-pilot, using the NMEA signals produced by the on-board GPS.

John, the skipper, reports that using the buttons to steer Lady Jane is 'too slow'. This could be an indication that the hydraulics pack needs work. By the screeching noise the 110V DC motor makes, I'd say that's very likely.

Anyway, there you have it. Obviously there is more than one project relating to the steering awaiting my attention.

5 comments:

  1. Anonymous6:59 PM

    Thanks very much Tim, I had been wondering. And it's not at all what I had expected.

    I imagined a small cylinder driven directly by the wheel (or electrical or mechanical equivalent) and then some electrics and the big hydraulic setup to servo the rudder to that input.

    Most interesting.

    If the electrics consists only of the hydraulic power pack and the hydraulic solenoids, you can likely swap it out for a 24 volt setup from a tractor or lorry. You could run a hydraulic pump right off your donkey or main engine (or both) and get rid of the electric one completely -- though you'd have to run lines out to the steering locker.

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  2. Tim,
    If you want to take a ride I think you had better put the steering closer to the top of your priority list.

    Bill Kelleher

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  3. Hi Anonymous.

    Like everything, It's all a matter of priorities.

    Regards

    Tim

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  4. Hi Bill

    The issues with the steering are minor niggles, particularly the hydraulic oil leak.

    The steering still all works perfectly fine.

    Regards

    Tim

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  5. Hi there IE

    I doubt that my steering mechanism could be classified as a complex system.

    Regards

    Tim

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