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nzmal · 28-12-2018, 17:42

We've just had our wheel steéing system upgraded to hydraulic and arrived at the boat today...
An autopilot was installed at the same time. We haven't left the marina yet or powered up autopilot but I've tried turning the wheel and...
When I turn to port I get 7.5 rotations lock to lock... when I turn back to starboard it's only 5.5 turns...?
There was initially hydraulic fluid weeping from a screw cap on the top of the wheel pump but this has stopped. Anyone able to shed light on what is going on here? Maybe the system need bleeding or I should run the auto pilot to settle it in?

billknny · 28-12-2018, 17:51

I guess my first question is what kind of ratio did you specify the steering at?

I sailed a 96 foot schooner that was 7 turns lock to lock, but that ratio seems wildly excessive for a "normal" sized boat. Even five and a half seems unreasonably low response.

Close quarters handling with a wheel that is over three turns to "hard over" must be a world of fun...

bad.wabbit · 28-12-2018, 22:15

A WAG... Read the description of types of cylinders https://www.cylinder.co.uk/technical...der-types.html. If only one cylinder is used for steering, then it is of the double acting type. And if you want to have the same number of turns at the wheel, then the cylinder needs to be non-differential, or balanced. For an autopilot hydraulic ram the latter is not necessary and often not provided. See what your ram is.

Uncle Bob · 28-12-2018, 22:29

Have you by any chance contacted the installer and asked the question ?

nzmal · 28-12-2018, 23:09

Quote:

Originally Posted by Uncle Bob

Have you by any chance contacted the installer and asked the question ?

Thanks Uncle Bob. Yes that's initiated but probably won't get a response until the New Year. We've moored out to a close anchorage without problems. Maybe it's just buyer anxiety.

motion30 · 29-12-2018, 00:03

Sounds like they used an unbalanced steering Ram. Not Unusual or any issue. Easy to tell when viewing the hydraulic steering Ram is there a rod sticking out of both ends or just one side

boden36 · 29-12-2018, 01:18

I would be inclined to bleed the system again. Your seepage is probably from compressed air in the system expanding and displacing fluid. If you have a manual valve that interconnects the two sides of the system ( to free the rudder), open that valve and push the rudder backward and forwards a few times. Then with the valve still open , spin the wheel for a while. The idea is to cycle the air back into the pump reservoir where it can bubble out.
If you have an autopilot pump, you can run that to make sure no air is trapped there.

One way of checking whether what I am saying is true, is to have someone hold the wheel whilst you push backwards and forwards on the rudder arm. If there is air in the system on one side, that side will be bouncy. You can do the same thing with the wheel against the rudder stops but it won't be so noticeable.

Regards,
Richard.

nzmal · 29-12-2018, 10:23

Thanks Richard. That's what I'll do today. Very sound advice. There is a valve that creates a fluid path between the two ends of the ram through a line parallel but external to the ram ( so that must be to free it up and allow emergency tiller to work without ram resistance?)
The ram doesn't have piston at both ends so appears to be "unbalanced"
The ram itself is old and part of our old system ( no autopilot and chain driven steering down to a pump and hydraulic ram... new system has pump at wheel and autopilot pump)
It makes sense to presume air will be in the New installation.

bad.wabbit · 29-12-2018, 10:35

If the ram is unbalsnced, then the installer should have made it clear to you how your helm was going to act. Bleeding the lines is as lo good but won't change the mismatch in turns. If the ram is from the old AP system, consider getting a new one. If the vendor specified it, work with him. It would annoy me to no end to sail with that setup and may be very distracting during docking, etc.

S/V Alchemy · 29-12-2018, 12:50

Quote:

Originally Posted by bad.wabbit

If the ram is unbalsnced, then the installer should have made it clear to you how your helm was going to act. Bleeding the lines is as lo good but won't change the mismatch in turns. If the ram is from the old AP system, consider getting a new one. If the vendor specified it, work with him. It would annoy me to no end to sail with that setup and may be very distracting during docking, etc.

It needn't be. Purchase a rudder angle indicator, and ignore the number of turns. It's the nature of the actuator.

Sea Angel1 · 30-12-2018, 01:37

you are stating, that there is only a rod on one side of the hydraulic cylinder. This means, that you have a differential cylinder. The ratio 7,5/5,5 is the difference of volume on the bottom side and the rod side of the hydraulic cylinder. The cylinder bore is twice the cylinder rod size. You should install another hydraulic cylinder with double rod ends with two identical rod dia. Then you Problem will be solved. How the autopilot is connected to your hydraulic system I cannot see, then I must have a hydraulic circuit drawing. But that system will not work well, because the autopilot pump has only 1 flow. Because the volume into PS is different as to SB , the reaction time will be different, because the pump flow is constant and the required volume is different. So a strange steering effect will occur. So change your hydraulic cylinder.

Sea Angel1 · 30-12-2018, 01:47

Another effect is that in case of manual steering you must turn the wheel to one side always appr. 35 % more then to the other side.

Uncle Bob · 30-12-2018, 01:54

Quote:

Originally Posted by Sea Angel1

Another effect is that in case of manual steering you must turn the wheel to one side always appr. 35 % more then to the other side.

Damn, I knew there was something wrong with mine, equal turns lock to lock.

JOHNMARDALL · 30-12-2018, 07:40

The pump on your system contains a ring of small pistons which pump the oil as you turn the wheel. The action of these pistons causes variances in the oil level in the body of the pump, which acts as the oil reservoir. To allow for those variances in oil level, there is a tiny air bleed hole in the filler cap at the front top of the pump body and that's where the leakage is occurring. On some installations, when the oil level is such that there is no longer leakage, there is also not enough oil in the pump to allow all of the pistons to operate smoothly and the wheel movement becomes "lumpy". To prevent this, it's best to connect a small reservoir above the pump using one of the blank plugs on the back of the pump body and then replacing the vented fill plug with a solid plug (most pumps are supplied with both plugs in the box). The reservoir can go anywhere that's convenient provided that the hose run from the pump to the reservoir rises without any dips.

The number of turns of the wheel to go from hard over to hard over depends on the ratio of the capacity of the pump (volume of oil pumped in one revolution) and the volume of the cylinder (volume of oil required to move the ram from one end of its travel to the other end). For example, a 20 cc pump acting on a 100 cc cylinder would require five turns to move the ram through its full travel. If you are unhappy with the number of turns of the wheel required to go from hard over to hard over, it may be possible to exchange the steering pump for a larger model.

Most systems are set up so that the ram is in the center of its travel when the rudder is amidships (straight ahead), The rudder movement may be limited by stops, or simply by the hydraulic ram reaching the end of its travel, with the internal piston ring against the end cap of the cylinder. A good rule of thumb is that the rudder should stop at 35 degrees either side of amidships/centered to avoid stalling of the flow over the rudder. That you have an unequal number of turns either side of amidships to full hard over suggests that the rudder and ram are not aligned (simultaneously centered). This can be remedied by installing a bypass line and valve to short circuit the cylinder, so that with the bypass valve open, the rudder and ram can be centered and then locked into relative position by closing the bypass valve. A secondary benefit of the bypass valve is that it allows emergency steering by a tiller on the rudder post/stock if the hydraulic system fails.

The electro-hydraulic pump controlled by the autopilot and the wheel pump must each be protected by a non-return valve, and if you are using nylon hoses a pressure relief valve should also be installed in the system to prevent the hoses "pumping up" when the wheel is pushed to hard over and putting back pressure on the pump, causing it to lock up completely or become very hard to move. Check the amperage rating of the electro-hydraulic pump before you use the autopilot. If the pump draws more current than the autopilot can handle (usually ten amps but read the auto pilot specs) the autopilot must be separated from the pump motor by relays, adequately rated to handle the current the pump motor draws. Failure to make this installation correctly will burn out the autopilot in seconds.

I hope this helps. Please contact me direct (jmardall@comcast.net) for more information or questions.

Good luck
John Mardall
Vetus Maxwell Boat Equipment