Hydraulic steering issues

Really need to know what "jumping in the steering" is?

Next questions; When did it last work correctly?
Any last service to the rudder post or Hynautic system?
Issues dock side or under way?

First guess, rudder chatter (rudder post binding).

If you have to build pressure for the rudders to react and then they “jump”, it means the rudders are binding. It is not an hydraulic issue.

does it happen both way, stbd and port? Could be something in the linkage between the piston and the rudder tiller

Oh Sheet
The old Hynautic power assisted nightmare.
Oh, abuse us more; A power assist pump on each engine?

Run Tylerloom, Run..

Sadly, I know about this mess.
Let me enjoy the rest of the night and compare better notes with you in the morning,, when I have the nerve and strength.
In preparation; reaching for another liquid bravery now.

First coffee in hand.

The old Hynautic power assisted steering (rudder tiller) system;
When new, properly installed, you could turn the helm wheel with a wet cigarette. This was a sweet system at its time.
You also had no feed back and hard to feel when the rudder was hard over against the rudder stops.

Theory of operation first;
That small cylinder with all those hoses is what your helm is connected to.
When the helm is turned, it pushes against the rudder tiller. When there is resistance against this ram from the rudder tiller, that lil servo valve is pushed & pulled against.
This lil servo valve directs pressurized hydraulic fluid to the second (larger) cylinder to assist the helm pressure against the tiller.

The chatter you are experiencing is this servo valve turning off, on, off, on quickly, pulsating fluid bouncing that larger assist ram like a jack hammer.
I have witnessed the mounting bolts on this large assist cylinder about to rip out of the rudder pillow because of this chatter.
Oh, when on auto-pilot, just the constant lil micro AP adjustments would cause a notable vibration thru the boat like a big gatling gun.

Before you start thinking more about that servo valve, all of the problem is not just there.
How that valve is dampened is a contributor to the pulsing/chatter issue.
There were internal & external damping springs. Even rubber bushings experimented with trying to slow down the valve reaction.
Hynautic stopped supporting this setup many years ago and tried to push an all-in-one design.
Then Hynautic merged with Teleflex.
Then Hynautic/Teleflex was bought up by Sea-Star.
Then Sea-Star was bought up by DumbMetic.
Now out cast as Bay-Star.

As you probably have found out the sad way; There is no support on this stuff any more.
If your lucky, You may find some old guy sitting in the back of some old shop that may remember the feel of a properly installed valve but alas, no parts.
Anything on e-bay is the last of the dinosaurs that you don't want.

But wait, there is more;
The engine mounted pumps; Are old, abused and not supported any more also.
The pressure regulators in these pumps are probably stuck wide open.

So now your thinking about that later all-in-one thingie.
Yes, Sea/Bay-Star remembers what it is. You still may be able to purchase one.
You will need a new pump or two and new pump regulators also.
You will end up with still old technology that is near or at end-of-life already.

There is 3 ways to fix this.
1) Spend hours and hours trying different springs in that servo valve and try to dampen its operation.
If / when this is completed, you will probably loose most of the power assist and have lost some of your finger tips.

2) Spend lots of bux and purchase the latest fancy steering system. There is a mix of hydraulic and electric models available now.

3) As I have done a few times now. Shop for a new MSV-21 valve, remove all the power assist stuff, go to a manual system. That larger assist cylinder will now become your primary steering ram.
The operator may never really feel a difference. Just maybe an extra turn for full port/stb swings.

I hope this helps.

As you may have been thinking, I am not a high-tech, tech.
Rather a budget orientated (red-neck), that has already had his finger tips whittled down a few times and been around some blocks.
Safety and reliability have always been proven in my work.
If you need better notes, let me know.

I'm off now to test a new propeller in gator infested waters.
What's left of my fingers are crossed.

Why do you even need power steering on a boat that size? I have non assisted hynautic on my 53 hatteras. No need for power steering

My 58 Bertram has a manual Hynautic system.
It was a Hatt 65 and 75 that I removed the power assist junk from. They don't miss it a bit.

For the performance freaks, Those belt driven pumps must take off a few HP

The simple thing to start with is disconnecting the rudder from the whole assembly to determine if its a mechanical issue like binding as Pascal suggested or a Hynautic issue like Capt Ralph suggests.