Rack and pinion steering autopilot oscillations

[Vangaboom]

We have a 41ft sailboat with Jefa rack and pinion steering. We're very much happy with the system when hand steering, it has not play at all, feels very solid, and no more problems with chain falling off because there's no chain.

But when the autopilot is on, the wheel oscillates quite a lot, especially when we change the course or tack. It steers the boat alright but we're concerned that the oscillations will lead to increased wear and tear and might cause a failure at the wrong moment. The oscillations do not go away even if we remove the steering wheel.

The autopilot is a Raymarine Evolution ACU 400 with linear actuator type 2.

We tried every setting in the autopilot configuration.

Does anyone know how to mitigate that or if we should care about it at all?

[Sailingallday]

Mine does the same. The only success i have had is to turn the response level way down. It chills a bit then but still not perfect

[SailingHarmonie]

Originally Posted by Vangaboom

We have a 41ft sailboat with Jefa rack and pinion steering. We're very much happy with the system when hand steering, it has not play at all, feels very solid, and no more problems with chain falling off because there's no chain.

But when the autopilot is on, the wheel oscillates quite a lot, especially when we change the course or tack. It steers the boat alright but we're concerned that the oscillations will lead to increased wear and tear and might cause a failure at the wrong moment. The oscillations do not go away even if we remove the steering wheel.

The autopilot is a Raymarine Evolution ACU 400 with linear actuator type 2.

We tried every setting in the autopilot configuration.

Does anyone know how to mitigate that or if we should care about it at all?

What are you expecting? The wheel and the rudder are connected. If the autopilot moves the rudder the wheel must follow.

When you are close hauled the rudder (and whell) should not move much at all. When you are sailing downwind, more rudder correction is required, and so the wheel will move more.

If the wheel is constantaly moving back and forth to hold a straight course, there are three possibilities:

• Your boat is inherently unbalanced.
• Your sail trim is bad.
• The tuning on you autopilot is incorrect.

Of course these are not mutually exclusive, and all can be present to varying degrees.

Can you steer the boat by hand with very little rudder movement under conditions where the Autopilot is waving the rudder all over the place? If true, then the autopilot tuning is the first issue to address.

If the rudder movement when the autopilot is in use is more or less similar to how much you move the wheel hand steering under the same conditions, look to improving your sail trim.

[Vangaboom]

The sail trim and balance are OK and the boat can be hand steered with minimal effort in your usual conditions.

What happens is that the autopilot keeps the boat on the correct course, making smaller adjustments every now and then, nothing out of the ordinary. But the adjustments, instead of being one or two longer, smooth wheel movements, often turn into several short jerks. It looks as if it tried to move the rudder to a new position in multiple smaller steps instead of one continuous movement, which causes the wheel to bounce back and forth until it settles again.

It's most prominent when we make larger course adjustments, say 20 degrees or more, otherwise less so.

What we already tried:
- There doesn't seem to be any play anywhere when hand steering.
- There's nothing interfering with the compass.
- Switching from Cruising to Leisure mode helps a bit.
- Increasing rudder damping maybe helps a tiny bit.
- Removing the wheel doesn't help, though for obvious reasons we only tried it when parked so there was little pressure on the rudder.


SailingHarmonie thank you for your advice but I think you may be referring to a different kind of oscillations, similar to what happens when a boat broaches and the autopilot can't keep the boat on course.

[Bowdrie]

See if the rudder position sensor is operating smoothly and without any slop in its linkage.
If the position sensor has any internal/external problems the AP will lose some of its ability to know what's going on, so it overcompensates.

[wholybee]

Can you post a video of your steering wheel when this happens? It is normal for the AP to make steering adjustments slowly. It does this by turning the wheel just a little bit at a time it it is not able to smoothly run the motor slow enough. If your steering both has play in it then it will bounce a bit when there is a movement from the rudder end. I know you said there is no play, but you really can't tell just by feel. And it only takes a tiny bit.

One setting that is slightly harder to find and change but has a dramatic effect is hull type. You have choices of Sail, Sail Slow Turn, and Sail Catamaran. The main difference between these is how much and how fast the wheel is turned. A faster turning boat needs the wheel turned less and slower than a slower turning boat. Maybe changing to Sail Slow Turn will cause larger wheel movements and minimize the problem.

From the commissioning section in the manual:

Vessel hull type selection
The vessel hull type options are designed to provide
optimum steering performance for typical vessels.
It is important to complete the vessel hull type selection,
prior to performing dockside calibration, as it forms a key
part of the commissioning process. The vessel hull type
options can be accessed at any time when the autopilot
is in Standby, from the [Vessel Hull Type] menu: [Menu >
Set-up > Autopilot Calibration > Vessel Settings > Vessel
Hull Type].
Select the option that most closely matches your vessel’s
hull type and steering characteristics:
• [Power]
• [Power (slow turn)]
• [Power (fast turn)]
• [Sail]
• [Sail (Slow turn)]
• [Sail Catamaran]

[deblen]

Check hardover time per manual.
Your steering piston maybe too fast.
Len