Hydraulic Steering Issue - Rudders Don't Keep Alignment on Cat

[InsuredApple]

I've got a catamaran with hydraulic steering. Both hydraulic rams have been rebuilt 3 times, to stop them from leaking, in an attempt to resolve the alignment problem, but the rudders still lose alignment.

There still appears to be a very minor leak on the starboard ram.

Why could this be?

The only way that I can think of is that there is a leak in the hydraulic tie bar (the hydraulic line connecting the port and starboard rams).

Or could there is a pressure issue that causes too much pressure in one of the chambers?

So confused. We've had MultiTech (sub contracted to Signature Marine) and Marine Hydraulics work on this. Well over $7,000 and still no resolution.

[redneckrob]

Originally Posted by InsuredApple

I've got a catamaran with hydraulic steering. Both hydraulic rams have been rebuilt 3 times, to stop them from leaking, in an attempt to resolve the alignment problem, but the rudders still lose alignment.

There still appears to be a very minor leak on the starboard ram.

Why could this be?

The only way that I can think of is that there is a leak in the hydraulic tie bar (the hydraulic line connecting the port and starboard rams).

Or could there is a pressure issue that causes too much pressure in one of the chambers?

So confused. We've had MultiTech (sub contracted to Signature Marine) and Marine Hydraulics work on this. Well over $7,000 and still no resolution.

Do both rudders move freely when disconnected from the steering system? I had a frozen spherical bearing on my Mahe 36 that made one of the rudders really bind, and it would cause the rudders to become misaligned since at times one rudder wouldn't move while the other did.

[InsuredApple]

Originally Posted by redneckrob

Do both rudders move freely when disconnected from the steering system? I had a frozen spherical bearing on my Mahe 36 that made one of the rudders really bind, and it would cause the rudders to become misaligned since at times one rudder wouldn't move while the other did.

Thank you for making time to reply.

Yes, both rudders move freely when the hydraulic rams are disconnected from the rudder arm. The boat was hauled out, during the time when the hydraulic rams were rebuilt the 3rd time. That's when I discovered that the rudders could move freely, and the rudder arms destroyed both of the rudder angle indicators; because the rudder arms were not secured.

[44'cruisingcat]

First I'd make a serious effort to ensure the system is completely bled of air. Any air in there could have you chasing your tail for ever.

In the absence of air, there must be a leak in the system, either in the hydraulic link, or in one or both rams.

It would be worth finding if the hydraulic link is effectively getting "shorter" or "longer", ie is fluid leaking out of the link or into it?

Work out if fluid leaving the link would cause toe in or toe out, and which one is happening.

If fluid is leaking in it could only be due to the piston seals in the rams passing.

A leak out could similarly be piston seals, but could also be shaft seals or leaking hoses, connections etc.

[InsuredApple]

Originally Posted by 44'cruisingcat

First I'd make a serious effort to ensure the system is completely bled of air. Any air in there could have you chasing your tail for ever.

In the absence of air, there must be a leak in the system, either in the hydraulic link, or in one or both rams.

It would be worth finding if the hydraulic link is effectively getting "shorter" or "longer", ie is fluid leaking out of the link or into it?

Work out if fluid leaving the link would cause toe in or toe out, and which one is happening.

If fluid is leaking in it could only be due to the piston seals in the rams passing.

A leak out could similarly be piston seals, but could also be shaft seals or leaking hoses, connections etc.

Very smart, that makes logical sense.

At this point, then, I'd guess that fluid is leaking out of the link (liquid tie bar) because the rudders are closing in, coming together.

Is my thinking right, or am I missing something?

[InsuredApple]

This is a rough diagram that I quickly whipped up... just to show our hydraulic system, the bypass valves (green), the liquid tie bar (blue)...

[skipperpete]

Where does the auto pilot fit into this, how does that work in this schematic? Is there a lock/shuttle valve somewhere?.... maybe in the helm pump.

[RaymondR]

Do the hydraulic lines actually come out the side of the cylinders as you have drawn them?

[smac999]

Can you not put a mech tie bar on? The cat I was on last week had one behind the back deck.

Is this how most cats are? Seems they would all be miss aligning over time.

[44'cruisingcat]

Originally Posted by InsuredApple

Very smart, that makes logical sense.

At this point, then, I'd guess that fluid is leaking out of the link (liquid tie bar) because the rudders are closing in, coming together.

Is my thinking right, or am I missing something?

It depends. On where the hydraulic link is set up on the rams, and on how the rams are set up on the tillers.

You need to look at the whole system and work out what would happen if fluid leaked out of the tie.

[44'cruisingcat]

Originally Posted by InsuredApple

This is a rough diagram that I quickly whipped up... just to show our hydraulic system, the bypass valves (green), the liquid tie bar (blue)...

For example, if your hydraulics were set up like this, with the tillers forward of the rudder shafts, and you were losing fluid from the link (blue) line, your rudders would toe out.

However, with the same set up, but with tillers aft, and they'd toe in.

[44'cruisingcat]

Originally Posted by smac999

Can you not put a mech tie bar on? The cat I was on last week had one behind the back deck.

Is this how most cats are? Seems they would all be miss aligning over time.

Probably the majority of cats have some mechanical connection between the rudders.

But hydraulically linked systems can work well. My rudders basically never get out of alignment.

[Dave852]

You show the valves between the liquid tie bar and and the line going back to the helm. On my boat I also had pressure relief valves installed there. Basically a spring loaded ball bearing that I had cleaned the gunk out and looked fine. But in the end removing them solved my alignment problem. Newer helm pumps have the bypass built in to the pump so any bypass does not affect alignment.

[MIRELOS]

Had a similar problem on my FP60, was not a hydraulic problem but an auto pilot problem, spent countless hrs. with Furuno tech support, they are great and still things did not work, finally got a marine electrician I know to look at it, reprogrammed the auto pilot commuter from scratch. If you have made any repairs (changing any part of the system) you need to have the main computer to recognize it by reprogramming. It took me a year to get it right...thanks Tony T in NY for your knowledge

[deblen]

Originally Posted by InsuredApple

Very smart, that makes logical sense.

At this point, then, I'd guess that fluid is leaking out of the link (liquid tie bar) because the rudders are closing in, coming together.

Is my thinking right, or am I missing something?

Are you sure that the actual rudders are out of line?
Could it be that one of the rudder angle meters or it's sender are the problem? / Len