Disadvantages of Hydraulic steering
 

After the recent exchange with Bob La Londe, I realized that I have been praising the advantages of hydraulic steering systems
over cable. This may make others think that hydraulics do not have a downside, which is far from the truth. There are pitfalls to
be avoided and inherent quirks that the consumer needs to be aware off.

The first is that most factory hydraulic steering systems are either under spec or borderline adequate. The second issue is the
common criticism that hydraulic systems have no feel like mechanical systems do. Now that may not be important in a power boat
application, but it is on a sail boat, as water pressure on the rudder is a major indicator for balanced sail trim. the typical
valving on a steering pump prevents the rudder turning the steering wheel. Hence, the lack of feel. However there are things
called sail valves that selectively bypass the check valved pump ports. They are not cheap, but they exist.

Another common complaint is their inherent resistance to rapid helm movements. This is caused by inadequate oil piping between the
rudder cylinder(s) and the pump, which causes very high oil velocity and turbulence. Using larger pipes and valves make that
almost go away, but when manufacturers make 2"diameter 30 " long steering cylinders with 1/4" NPT ports, it certainly doesn't help
the turbulence issue. Seal failures can occur because of over pressure spikes. Most people think that just having an over pressure
relief valve is adequate. It isn't. If the piping size is too small for its length or the relief valve port is too small, the
pressure peaks can overwhelm the relief system and blow out seals.

There are other things to be aware of as well, but good design will eliminate many of the shortfalls of hydraulics rendering years
of trouble free service, but get it wrong and you'll see lots of grief.
Steve

Disadvantages of Hydraulic steering
 

On Tue, 28 Sep 2010 10:21:47 +0200, "Steve Lusardi"
wrote:

After the recent exchange with Bob La Londe, I realized that I have been praising the advantages of hydraulic steering systems
over cable. This may make others think that hydraulics do not have a downside, which is far from the truth. There are pitfalls to
be avoided and inherent quirks that the consumer needs to be aware off.

The first is that most factory hydraulic steering systems are either under spec or borderline adequate. The second issue is the
common criticism that hydraulic systems have no feel like mechanical systems do. Now that may not be important in a power boat
application, but it is on a sail boat, as water pressure on the rudder is a major indicator for balanced sail trim. the typical
valving on a steering pump prevents the rudder turning the steering wheel. Hence, the lack of feel. However there are things
called sail valves that selectively bypass the check valved pump ports. They are not cheap, but they exist.

Another common complaint is their inherent resistance to rapid helm movements. This is caused by inadequate oil piping between the
rudder cylinder(s) and the pump, which causes very high oil velocity and turbulence. Using larger pipes and valves make that
almost go away, but when manufacturers make 2"diameter 30 " long steering cylinders with 1/4" NPT ports, it certainly doesn't help
the turbulence issue. Seal failures can occur because of over pressure spikes. Most people think that just having an over pressure
relief valve is adequate. It isn't. If the piping size is too small for its length or the relief valve port is too small, the
pressure peaks can overwhelm the relief system and blow out seals.

There are other things to be aware of as well, but good design will eliminate many of the shortfalls of hydraulics rendering years
of trouble free service, but get it wrong and you'll see lots of grief.
Steve


And, every vendor I've run across has a calculation sheet, furnished
by the manufacturer, that sets out all the information and formulas
you need to calculate sizes.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)