Boat waltzing and oversteering on autopilot

[Irish Rover]

My boat is a Leopard 43pc with Raymarine electronics. I have a P70 ap head and I'm told the brain is a Ray Evolution autopilot.
Over the last couple of months I've noticed the boat seems to waltz and oversteer when I'm using the ap. If I make a 10⁰ turn on the ap it goes much further and comes back. It never seems to keep a perfectly straight course even in a flat calm sea. When I'm steering manually and holding a straight course the rudde indicator on the ap head shows around 8⁰ to stb.
When I turn the wheel manually the rudder indicator on the p70 shows 30 green full to stb but when I turn to port the indicator is less than 10 red when the wheel stops.
I've tried to do a "dockside wizard" calibration but failed. It asks me to put the rudders in the central position, which I'm assuming is when the piston marked in the photo is at half its travel. I measured the piston at just under 20 cm with it fully extended and put it just under 10 for the test. Next it asked me to turn the wheel full to port which I did and the piston was fully extended. Next all the way to starboard but I couldn't get it retracted beyond halfway. What am I doing wrong?
Gentle please. I'm not the most tech savvy guy around.

 

[spannerman]

I see you have an emergency bypass valve between the two hydraulic circuits, I would set rudder to straight ahead then open the valve which will allow you to get the cylinder centred.Also check the rudder position indicator these are adjustable and should have equal travel from straight ahead, if thats ok you should be able to fine tune the reading in the setup menu. It sounds like your cylinder has drifted off its centre position so you have more travel one way than the other.

 

[Irish Rover]

I would set rudder to straight ahead

Boat is in the water. How can I know when the rudder is traight ahead?

emergency bypass valve between the two hydraulic circuits

The blue handle valve?

Thanks for your reply.

 

[vas]

Boat is in the water. How can I know when the rudder is traight ahead?

The blue handle valve?

Thanks for your reply.

get to the open sea, carefully both engines same revs, wheel to wherever boat goes straight, mark the point in the rudder stock


yep, blue handle valve joins both sides of the hydraulic cylinder

btw, have you changed any settings in your a/p? from previous IT related questions you've posted in here, I'd guess no, unless by accident.
Establish straight and then go from it. Not familiar with Raymarine h/w but I guess you'll have to do both dock and open water calibration.

V.

 

[billskip]

get to the open sea, carefully both engines same revs, wheel to wherever boat goes straight, mark the point in the rudder stock

Well yes, but as it's twin rudder both maybe wrong and the straight line maybe compensation.
First, I would disconnect both ram links to the rudders, and turn the lever arm manually to maximum in both directions and mark the central position on both rudders, then get max and minimum operational stroke of the rams and centralise them, then see where the where the ram and lever links offer up...
As the rudders aren't visible it's a guess they will be "straight " between total distance of travel.

 

[PaulRainbow]

In addition to the above, i would re-calibrate the heading sensor.

 

[billskip]

In addition to the above, i would re-calibrate the heading sensor.

Yes, on the mechanical side I don't really see what could have altered anything, unless an encounter with an orca or two.
Likely Spannerman is correct the hydraulic ram ballance/ travel has altered, but there is probably a reason, like maybe seals in one ram letting by, or possibly air in the system or summat.