Hydraulic steering drifting

idpnd

idpnd

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www.svlibertalia.com
Hello all,

I've got a Capilano 275V with model 50 Uniflow valve from 1988 or so.Lately the rudder has been drifting up to the 5° mark in port over the course of a few hours; there is a strong cross current here.

I de-aired the system thoroughly and I felt there was a lot of air in it considering I had last done it 6 months ago. Checkvalves were also cleaned (oil clean, no grit).

The steering shows no other symptoms otherwise - works great on manual and autopilot.

Opinions?

Thanks for your time!
 
It seems that you may have a seal failure, assuming you do not have any leaks. Air getting in does suggest there may be a leak. If ther is no leak then either your pump or cylinder seals are leaking. Can you isolate the cylinder and the punp and then you could test whether there is a seal failure.
 
Not neccessarily, there are seals in the cylinder and the pump that could be allowing oil to slide from one side to the othere thus causing your drift. Without seeing a circuit diagram it is difficult to say if the check valves could be guilty
 
Hello again Peter, and many thanks for your attention!

Funnily enough, I have the full diagramme from the patent for this unit:

http://www.google.com/patents?vid=U...maxm_ap=1&as_maxy_ap=1974#v=onepage&q&f=false

These older capilanos have 3 lines - 2 going out and one feeding back to the helm. There is an autopilot somewhere in the middle. The setup is just as shown in the PDF (installation manual), except that there is a pump instead of the lower helm unit.

I cannot move the steering cylinder by hand, but I can see how the waves slapping (plus the tide here at Audierne) shift the cylinder very slowly, always and only to port, to a maximum of around 5°.
 
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I think I understand that you are in port with a strong cross current on the boat which is putting pressure on the rudder and you have no steering pump running. In this case it would seem nothing is wrong.
 
Hello engineer, thanks!

I am getting a bit unnerved because about to do first Biscay crossing ;)

The steering does work perfectly well under autopilot and manual.

I thought hydraulic steering is supposed to be rock solid at the rudder end of things?
 
I would tend to agree there is little seriously wrong and the autopilot or hand steering will easily keep up with any slight weeping. The valve system seems to be a relatively smart system that should weep very little, though it does act as a relief valve. The cylinder is the other potential point, what type op sealing is there in the piston, if it is an O ring type it may be worth replacing, if it is piston rings then they are probably good for years to come.

Whilst in no way suggesting that there may be any serious problems it would be common sense to carry replacement seals for the cylinder and have means of controling the tiller at sea whilst those seals are replaced.
 
If your steering is always drifting to port, then I might suggest that you also have an inbalance in your rudder, which means it is not running true. I had a similar problem at one time and cured it by fitting a trim tab to the back edge of the rudder. The trim tab was adjustable from the deck and was invaluable in being able to control the rudder independantly of the steering system.
 
maxi77 said:
I would tend to agree there is little seriously wrong and the autopilot or hand steering will easily keep up with any slight weeping
Click to expand...

Thanks again maxi, I do have an emergency tiller but no replacement seals and wouldn't know what to do with them anyway. Although I'm generally quite keen on a bit of DIY, I will probably get a professional company to overhaul it down in Spain since they don't make this uniflow valve model anymore, meaning it would be a total upgrade once it's gone.

Best regards
 
idpnd said:
Hello engineer, thanks!

I am getting a bit unnerved because about to do first Biscay crossing ;)

The steering does work perfectly well under autopilot and manual.

I thought hydraulic steering is supposed to be rock solid at the rudder end of things?
Click to expand...

Dont worry. I crossed Biscay in a Prout cat with hydraulic steering and exactly the same sort of drift.
 
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