Steering Gear Intermittent Fault 1

[zhone]

Hi,
I have an intermittent problem with steering gear where the ship goes hard to port of its own accord.This has happened on both autopilot and manual FU steering.The fault last only approx 30 seconds.We have Ulstein Tenfjord(Rolls Royce) steering gear and Anschutz Raytheon Autopilot.Have checked all the cards in the FU system.Tested outputs from each card, feedback signal and signals down to solenoids good.Has anyone else had issues like this?

 

[IRstuff]

You're probably better in forum672 rather than here, but the other forum is not particularly lively.

TTFN

FAQ731-376

 

[zeusfaber]

Intermittent steering hardovers really sap command confidence, and can be devils to track down, so you have my sympathy.

Is there any pattern to when this happens? Has it happened enough times to know whether any pattern is significant? Does it happen when people are doing breakdown drills? Is it always the same helmsman it happens to? Is it always the same control system, or the same pump?

Is the performance of the gear adequate the rest of the time - good positional accuracy and sweep times?

Before interfering with anything else, I'd have a quick look at the return line filters in your steering hydraulic system and judge from the state of those whether there's much chance of the problem having been caused by valves having got stuck open by debris.

Assuming the filters are clean, I'd then start going over the ship's cabling - starting with the rudder feedback signal, then along the FU demand path from Hand Steering Unit to Servo Amp. Tug twist and wiggle the cable at every loose loop, every plug break (especially!), and every bulhead penetration to see if you can recreate the symptoms. Once you've turned your intermittent fault into a hard fault, diagnosis becomes much easier.

A.

 

[zhone]

Thanks for your response zeusfaber.The filters have been checked and no debris.The fact that the problem happened on both hand steering and autopilot leads us to look at the common points.Each system is pretty much independent from a control point of view, the common points being the selector switch on the bridge and the solenoid drivers and then the hydraulic equipment.We tried to simulate a loose connection and the steering stayed in position.

It is hard to get accurate info off the bridge crew.Everyone we speek to seems to have a slightly different take on things.The ship always goes to port when the problem happens.Another thing that was mentioned was that on the bridge the officer of the watch noticed that the light on the pushbutton switch for Pump1 went out and right away they selected Pump 2.

Could interference on the cables be an issue,either on the feedback cables or cables going to solenoid drivers?

I think we will have to focus on cable connections for a bit to really rule them out.

Thanks again for the help.

 

[zeusfaber]

On the whole, the fact that the bridge team are all telling you slightly different things is probably a good thing - means they haven't been conferring to cover up some cockup of their own.

What follows is just a few more random thoughts - certainly not a concerted plan of action.

How often is this happening? Is it common enough to make it worth your while closing up a watchkeeper in the tiller flat to see what it looks like from down there?

Can you learn anything from the way the control system is laid out? I've seen some Anschutz systems where each pump has its own dedicated control system, and some where you can switch between systems, with the selected system being in command of all the running pumps at the same time. This is going to influence the way you interpret the history of how things were set when it all went wrong.

I can't see the cables going to the solenoids ever picking up enough EM interference to put the gear over - the power levels required to make any difference are too high. I suppose interference on the feedback cables could be possible in theory - but I've never heard of it happening in a ship's system (done it on aircraft controls, but that's a different story altogether).

You might look at what is meant to influence that Pump1 light - is it just an indication that the contactor in the starter is energised, or does it also indicate freedom from alarms? Is there any way of seeing whether the Hydraulic Lock Alarm was doing anything while the incident was in progress (this actually detects failure of the solenoid valve to respond to a demand, rather than anything exciting in the hydraulic front).

One thing I have come across in the past is an intermittent loss of one leg of the power supply to the feedback pot. I think all the Anschutz controls have a wire break monitor, so you ought to be protected against the same thing happening to the demand signal from the bridge.

A.

 

[chief]

There is a possibility that you are picking up intermittent electrical "noise" on your control cabling. Check your cable routing and see if it is running near a transformer or high voltage source and that cabling is spaced with sufficient space between routes. you can shield the cable by covering it with flexible conduit. Check the earthing philosophy and check the control cable and equipment is correctly grounded.
Check the control volts with a syncroscope to see that their are no peaks. Check the control cable sizing spec. Oversize cable will give oversize "noise".

Offshore Engineering&Design

 

[zeusfaber]

Chief could be onto something with his comment about earthing philosophy.

I've investigated a couple of incidents where steering gear has gone over to about 15 degrees and then stopped there - a displacement which, when converted to the same scaling as the HSU signal, matched suspiciously closely the difference we measured between earth at the QM console and earth at the SSP.

Most of our systems reference the signal to earth at the HSU, then use a differential input at the servo amp to take out the difference. It might pay to check that the signal cable down from the bridge isn't catching an intermittent local earth somewhere in the tiller flat.

A.

 

[powerjunx]

zhone, i'd been with these system exactly the same as yours. Though, slightly different problem, that is; frequent hunting of the rudder deflecting about 10-20 degrees either port or starboard.
With your case, great emphasis should be focus on Anschuthz (Ratheon) relay drivers control card inside the autopilot stand, if you have spare onboard try change this card to carry out your fault finding. Is the existing card an old one from Anschuthz?
furthermore, have you tested the outputs voltage of control relay (24vdc or 120VAC, depending system use) to drive the solenoid of the rudder both port and starboard upon directing the command signal of FU manual or auto mode?
please note, adjusting the control card for tuning the deadband, etc will affects the control responce of rudder. I suggest you should try to adjust these parameters on the control card, you will see multi-turn potentiometers which was labeled with each function.I'd tried to turn one of these potentiometer, id notice a deflection of rudder angle to about 20degree.
Nevertheless, consult the manual for the procedure of these adjustment..your problem lies with these control cards.
Good to hear you soon.



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