Boat waltzing and oversteering on autopilot

Irish Rover

Irish Rover

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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.
20260225_154619.jpg
 
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 said:
Boat is in the water. How can I know when the rudder is traight ahead?

The blue handle valve?

Thanks for your reply.
Click to expand...
get to the open sea, carefully both engines same revs, wheel to wherever boat goes straight, mark the point in the rudder stock
:cool:

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.
 
vas said:
get to the open sea, carefully both engines same revs, wheel to wherever boat goes straight, mark the point in the rudder stock
Click to expand...
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 said:
In addition to the above, i would re-calibrate the heading sensor.
Click to expand...
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.
 
Thanks for the replies. I don't have ready access to the port side steering - the generator is in that compartment and, as far as i recall, there's a bulkhead between the generator and the steering. The bulkhead is probably just sound damping but whether I'm nimble enough to get in there to remove it is another issue. I'll have a look today.
I found my manual and it gives a procedure for positioning of the rudders in the water. Basically it says run at 10 knots on a straight run and open both bypass valves for 20 seconds. So I need to figure out first if I can get at the port side, and I need a 3rd crew member, as I assume the valves need to be opened at the same time.
 
Just guessing here, but the autopilot has only one rudder sensor and assumes on catamarans that the rudders are both alligned with each other. If they are not then the autpilot will be trying to steer based on the rudder with the sensor attached, and if the other isn't alligned then this may cause the boat to slowly turn when the controlled rudder is on straight ahead - at some point the autopilot will correct and this may well result in an oscillating course.

Does it behave differently on Track compared to Mag heading?

Here is a link to someone who fitted a Raymarine Autopilot to his cat ... it might help ... but checking the rudders are correctly alligned and that the bypass valves are properly sealing when shut, followed by a recalibration (described in the autopilot manual) should fix it IMO.

Took me a while to get my AC400 Autopilot running properly when I fitted it last year, but mine is a monohull.

Raymarine autopilot installation on a Catamaran
 
As I suspected no way for me to get at the portside steering gear. It's a small space, very narrow because of the gen and there are sound damping panels fitted between the gen and the steering gear. I played around a bit with the stb side. I opened the valve and positioned the ram at what I think is the halfway point. I then did the dockside wizard setup, followed by the automatic calibration, and got a success message to both. The indicator on the p70 head shows rudder indicator going full green on stb and a whisker short of full red on port.
I'm waiting for my wife to call to come join me for a sea trial. If I can pick up the courage I may even get in the water to have a look at the rudders.
 
I went through all the AP settings before I went out. THe vessel type was set as powerboat, and I changed it to catamaran.
Went out for a spin. All seems to be OK but it's probably not an ideal day for a test as the sea is a bit rough. We anchored in a sheltered bay, and I got in with the snorkel mask on. Rudders look straight yo me looking at them individually, but the visibility wasn't really good enough to judge when I went back far enough to see both together.
I think I may have found the source of the trouble. The remains of a rope are still wrapped around the stb shaft. I suspect this may have been caught around the stb rudder and dragged it off centre. The rope doesn't seem to be causing a problem now, so I'll leave it until I lift the boat for maintenance in 10 days. I'll get a better look at the rudders then as well to confirm alignment.
Thank you all for your input.
 
If I remember right in Ray marine there is a setting for the type of boat you have.
It sounds like you have it set to heavy displacement sailing boat (aka fully loaded supertanker), when it should be set to something more reasonable.
 
westernman said:
If I remember right in Ray marine there is a setting for the type of boat you have.
It sounds like you have it set to heavy displacement sailing boat (aka fully loaded supertanker), when it should be set to something more reasonable.
Click to expand...
probably similar to a sensitivity setting on Garmin A/P. Also have to set the typical cruising speed of your vessel.
 
westernman said:
If I remember right in Ray marine there is a setting for the type of boat you have.
It sounds like you have it set to heavy displacement sailing boat (aka fully loaded supertanker), when it should be set to something more reasonable.
Click to expand...

vas said:
probably similar to a sensitivity setting on Garmin A/P. Also have to set the typical cruising speed of your vessel.
Click to expand...
As I mentioned earlier it was set to Powerboat and I changed it to catamaran. No setting that I could see for cruising speed.
 
Irish Rover said:
As I mentioned earlier it was set to Powerboat and I changed it to catamaran. No setting that I could see for cruising speed.
Click to expand...
Powerboat was the correct setting, you don't have a sailing cat. The options are:

• [Power]
• [Power (slow turn)]
• [Power (fast turn)]
• [Sail]
• [Sail (Slow turn)]
• [Sail Catamaran]
 
PaulRainbow said:
Powerboat was the correct setting, you don't have a sailing cat. The options are:

• [Power]
• [Power (slow turn)]
• [Power (fast turn)]
• [Sail]
• [Sail (Slow turn)]
• [Sail Catamaran]
Click to expand...
I'll check tomorrow but I don't think it said "sail catamaran". I'm happy to change it, if powerboat is more appropriate.
 
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