Our steering no.2 is hunting, and base on the instruction manual is incorrect adjustment on the servo control board. this adjustment is not stated in the manual. please help me how to adjust it in the servo control.. maker: yokogawa many tnx

04 Jun '17, 14:38

June 4, 2017, 2:38 p.m.
pogiako's gravatar image

1) Hunting in steering gear may be cause by internal leakages. During rudder movement hyd. oil supplied to one chamber of the steering gear hydraulic cylinder and drained from opposite chamber. When desired rudder angle reached and control solenoid valve de-energized oil in both chambers of hydraulic cylinder must be kept locked in order to fix the rudder position. This achieved by one or more counterbalance valves. If this valve has internal leakages it by-passes hydraulic oil from steering cylinder resulting in change of rudder angle. The Autopilot receives angle feed back and detect that angle is different from set point. It gives a signal to control solenoid to change rudder position back to set point.

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This example of counterbalance valve from our steering gear diagram.

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How counterbalance valve actually looks like.

Our suggestion is to check hydraulic system i.e. counterbalance valve(s) first as it subject to wear.

2) The other common failure is wear and/or loosening of rudder angle feedback linkages. If linkages geometry distorted Autopilot PCU receives wrong feedback signal resulting in incorrect operation. Check them for proper tightening and wear.

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05 Jun '17, 00:17

June 5, 2017, 12:17 a.m.
SeamenExchangeExpert's gravatar image

Thanks for your answer.. but I think the problem is in the servo control board ,because the solenoid activate port and stbd 1 degree only alternately with period of 0.5 seconds during in manual and auto pilot mode. and the result is the vessel is shaking. alt text

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05 Jun '17, 18:46

June 5, 2017, 6:46 p.m.
pogiako's gravatar image

Does hunting happen only underway or during port stay/anchorage also? Meanwhile (in case of Yokogawa Autopilot) open servo control board cabinet and pay attention to potentiometers:

  • VR2 (Dead band P)

  • VR3 (Dead band P)

  • VR6 (Feedback uSpan)

  • VR6 (Feedback uZero)

1) Compare above potentiometers of both servo boards #1 and #2. Carefully mark current setting and setup potentiometers of hunting servo board to same values of normally operating servo board.

2) If step 1 doesn't help try to slightly increase settings of VR2 (Dead band P) and VR3 (Dead band P) but remember to carefully mark current settings with a pencil so you can always set up backwards.

Dead band is a range of insensibility and if it is too small even minor rudder deviation will make servo board to re-adjust rudder position by activating of control solenoid valves.

Hopefully that helps. Please update on your progress.

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06 Jun '17, 02:43

June 6, 2017, 2:43 a.m.
KnowledgeBase's gravatar image

Good day sir, sorry for late update due to no internet signal. I followed your instruction by adjusting the VR2 and VR3 and the result is the steering gear is back to normal. no more hunting happen again. many thanks for your advice. its very helpful

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21 Jun '17, 14:02

June 21, 2017, 2:02 p.m.
pogiako's gravatar image

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