[DG] [DG11] CR hydraulic drive versus Type 3 linear hydraulic

[shparrot]

I have done everything to eliminate excessive hunting with my ACU 400, type 3 systems. I have two independent setups that both demonstrate the same tendencies. The boat is 57' sailboat, fully loaded displacement is 21000 Kg, the rudder assembly including quadrant and tiller arms is 60 Kg. Rudder is semi balanced. We've stiffened the rudder, reinforced the ram mounts and moved the EVO sensor. There is no play in the assembly.
With rudder sensors connected and rudder damping at 9, and every conceivable combination of hull type and responsiveness setting the system will ocaissionaly go into rapid oscillation. Can only be stopped by grabbing the wheel. Additionally at these settings response is sluggish and course keeping in any kind of seaway, above 2 meters, very poor.
Without the rudder sensors there is no oscillation but course keeping is not very good.
I think there is nothing left to do. So two questions.
Initially I connected the two ACU's to one rudder sensor. Only one ACU at time was powered but one of your tech's mentioned I might have damaged the sensor power supplies in the ACU's. Could this cause these symptoms?
Would replacing the units with ACU 300's and a CR pumps be likely to solve this problem. If so do you have any recommendations for a hydraulic ram?
Thanks

[Derek - Raymarine - Moderator]

Hi shparrot,

Thankyou for your enquiry.

The first point to make is that the two ACUs should not be connected to the same rudder reference unit, they should only be connected to their own transducer, OR use a relay operated by a change over switch to isolate one ACU from the transducer when not being used.

The rudder oscillation you describe is generally caused by the natural flexibility within the steering system and will always be worse when the boat is alongside - usually the water pressure on the rudder when the boat is underway will damp out this flexibility. Further background to thiscan be found here.

The modifications that you have made are all the correct course of action to take, you have not mentioned checking the operation of the rudder reference unit to make sure it is smooth and mounted such that is accurately reflects the movement of the quadrant - any amplification of the movement, flexibility in the mounting of the transducer will also trigger this instability too.

You mention a T3 system, is this the T3 hydraulic linear drive? if yes, then check the drive type selected, sometimes the drive type needs to be set to Mechanical linear not hydraulic depending on how sensitive the steering is.

I would also add that we are introducing new software in the next 1-2 months with some improved performance characteristics for larger vessels - primarily power vessels, but one of the changes we have introduced is a modified rudder damping protocol and this will help you out too, you will find that a damping level of about 7 will be better for your application than the current version at 9. Please keep an eye on our website as the software will be launched there as a free download.

I hope the above helps?
Regards
Derek

[shparrot]

Thanks Derek
After the initial installation, I connected a separate transducer to each ACU. Could I have damaged anything in the ACU's? They were never live at the same time.
I'm going to move the rudder transducers so they read from the tiller arms rather than the quadrant. I strongly doubt it, there might be some torquing between the arms and quadrant.

[Derek - Raymarine - Moderator]

Hi shparrot

It is possible that the ACU may have been damaged, the only way to test is to individually connect each ACU to its own Rudder reference unit and test the rudder angle operation.

The key is to ensure that the rudder reference arms move equally and proportionately to the movement of the rudders.

Regards

Derek