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Old 14-03-2019, 18:56   #1
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Hydraulic steering off center?

Hello wise forum,

I am relatively new on the forum and recently took the jump and bought a new to us, 1980 Carter Offshore 50' sailboat. A bit of an unusual boat with 2 nearly equal masts carrying 2 self tacking jibs. I believe it is known as a Staysail Schooner with a Luna rig. However I digress.

The steering is a "passive" hydraulic system (no externally powered pumps): a manual pump at the helm actioned by the the wheel turning and a hydraulic cylinder at the rudder, acting on an arm off the rudder itself.

I found that the cylinder is leaking moderate amounts of hydraulic fluid (oil) which I can top up periodically for the time being. More confusing is that I find that the tiller does not sit in the center when the wheel is in the middle between its Port and Starboard stops. It appears that the maximum rudder angle is greater to starboard (approx 50 degrees from centerline) than it is to port (approx 30 degrees from centerline).

I am wondering if the piston can loose it's central position within the cylinder due to a leak or air bubble? Or is it possible that it was originally installed off center to compensate for some effect (prop walk?). The previous owner never knew about it .... Your thoughts are greatly appreciated!
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Old 14-03-2019, 19:08   #2
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Re: Hydraulic steering off center?

you need to be under way to see what the tiller position is,and if it is central,

it is quite possible markings on the steering wheel have changed due to fluid loss and appears to be no longer central if marked by a bit of tape or knot on the wheel.

hydraulic ram is also quite possibly mounted with say 30 degrees to port and 35 degrees to stb max turning arc,but should not really be an issue.

leaks on the ram are easy to fix with new seals and orings,then system bleeded as long as there is no corrosion on the shaft or scoring.
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Old 14-03-2019, 19:15   #3
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Re: Hydraulic steering off center?

Thanks Atoll, great to get such a quick response! I agree that the arcs should be around 30 to 35 degrees to each side but I am seeing a larger angle than this (at least to starboard). I had marked the centre on the wheel with a bit of tape by counting turns and tapping at the half way between stops. Probably not the correct approach. I plan on reviewing while sailing as you suggest.
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Old 14-03-2019, 19:32   #4
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Re: Hydraulic steering off center?

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Originally Posted by Bambooboat View Post
Thanks Atoll, great to get such a quick response! I agree that the arcs should be around 30 to 35 degrees to each side but I am seeing a larger angle than this (at least to starboard). I had marked the centre on the wheel with a bit of tape by counting turns and tapping at the half way between stops. Probably not the correct approach. I plan on reviewing while sailing as you suggest.
30-35 degrees was just an average,probably 40-45 degrees would be a better example this would depend on lenth of lever arm and the stroke lenth of the ram.
i doubt if there is an off set that has been done for prop walk ,more likely just a poorley centralised installation due to space constraints
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Old 14-03-2019, 21:44   #5
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Re: Hydraulic steering off center?

What Atoll said, but I'll add some more info.


In the systems I've designed and used in the past, the wheel drive is just a simple pump. There will be leackage by the pistons/balls that just comes with age. Not that it leaks out, it just leaks by the rings if it has any. The way to test this is to go hard to stop and keep the torque on the wheel. If it slowly continues to rotate it's either bypassing in the pump or the cylinder piston is leaking from one side to the other. You may have to rely on a rudder angle sensor or linear pot sensor that's on the auto pilot if you have one.


As far as +30 and -35 scenario this can be corrected but is probably not worth it. To get it dead on the PO would have had to make sure the bell crank was perpendicular to the hyd cylinder which was dead on 1/2 stroke, and then mount the far end it.
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Old 15-03-2019, 10:01   #6
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Re: Hydraulic steering off center?

We just had our Hydraulic cylinder (balanced) rebuilt because of minor external leaks. The major issue was internal leaks past the Piston causing us to steer constantly to starboard while sailing or motoring. Our Hydraulic system has a bypass at the cylinder where adjustments can be made to center the rudder and the sweep to both port and starboard.
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Old 15-03-2019, 10:23   #7
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Re: Hydraulic steering off center?

Quote:
Originally Posted by Bambooboat View Post
Hello wise forum,

I am relatively new on the forum and recently took the jump and bought a new to us, 1980 Carter Offshore 50' sailboat. A bit of an unusual boat with 2 nearly equal masts carrying 2 self tacking jibs. I believe it is known as a Staysail Schooner with a Luna rig. However I digress.

The steering is a "passive" hydraulic system (no externally powered pumps): a manual pump at the helm actioned by the the wheel turning and a hydraulic cylinder at the rudder, acting on an arm off the rudder itself.

I found that the cylinder is leaking moderate amounts of hydraulic fluid (oil) which I can top up periodically for the time being. More confusing is that I find that the tiller does not sit in the center when the wheel is in the middle between its Port and Starboard stops. It appears that the maximum rudder angle is greater to starboard (approx 50 degrees from centerline) than it is to port (approx 30 degrees from centerline).

I am wondering if the piston can loose it's central position within the cylinder due to a leak or air bubble? Or is it possible that it was originally installed off center to compensate for some effect (prop walk?). The previous owner never knew about it .... Your thoughts are greatly appreciated!
Your offset cannot be from leaking. The only way to have that difference is in the piston mount. A few pistons have adjustment slots where the bolts mount the piston to the boat. A few have 2 U-clamps that the piston can slide through.

Most have 2 or 4 holes, and the only way to set it is to re-drill the holes.

If you had a make and model number, we could look it up and tell you what you need to do.

But it is also possible - although highly unlikely - that the steering was set this way because the boat doesn't track straight, or the prop walk when backing needed to be countered by the extra turning angle.
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Old 15-03-2019, 16:31   #8
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Re: Hydraulic steering off center?

Again thanks to all for your comments and insights. Sure helps to hear what others think :-).
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