Hydraulic steering sizing

[Larry aberg]

I I need help on figuring out how to improve the hydraulic steering system on my 55 ft powerboat.

The issue is during conditions when we are running with waves and surfing down the waves the forces on the steering wheel are more than the system can exert. The wheel is solid no matter what force you apply to the wheel

We generally pull the power back to slow down or end up doing lots of S turns down the coast.

It doesnt take much of a swell to put us in the scenario.

The boat is heavy displacement meaning full of fuel and water 52,000 lbs semi planing hull.

The hydraulic system is a 1.7L helm pump and 1.7 cu inch ram. It looks like thermoplastic hydraulic lines with copper fittings and compression fittings.

There is a auto pilot pump installed with a course computer and goes to max during the conditions above unable to keep a course.

The system works fine in calm waters.

I’m assuming the hydraulic steering system was not designed for this size boat?

What size Ram and helm pump should i be looking at?

Recommendations?

Topic

[Rob Schepis]

You have not provided the corrected cylinder specs. And you said that the helm pump is “1.7L” … is that 1.7 cu in ? It sounds like the system is undersized in more ways than one. My research is telling me that the helm pump should be 2.7 cu in, not 1.7 cu in, your 3/8 nylon tubing should be 5/8 copper tubing with proper hydr. hose, and the cylinder should be close to 30 cu in. There are other variables to. What size (diameter in inches) is the helm wheel? You can review manufacturer specs. Here is a page on rudder torque calculation.

[Larry aberg]

Hi Rob,

If this was a new build what is the process of calculating the size of the steering components like the ram, helm pump, auto pilot pump?

Are there specific formulas used to calculate the loads on the steering system

Larry

[Larry aberg]

This is a factory boat no extension by me. I believe the factory added the cockpit from their model w/o and came up with this model.
7.5 turns on thd wheel full stbd to full port.
The helm pump is a seastar 1.7L model. I will get some pics of the hydraulic lines and ram setup.

The AP holds rudder but during ocean conditions cannot turn the rudder to hold a straight course. The Ap during high stress times sounds very loud

[Rob Schepis]

Larry aberg wrote:

The hydraulic system is a 1.7L helm pump and 1.7 cu inch ram. It looks like thermoplastic hydraulic lines with copper fittings and compression fittings.

I re-posting your pic correctly oriented.

Rudders are far forward, was this boat extended? Do you know what the total rudder arc is? The AP should display rudder position.

So the cylinder holds the rudders position even under high load but the helm pump cannot move it, is that right?

Trying to calculate your turns lock-to-lock I realize your specs are wrong for the ram, please repost.

How about model numbers of your helm pump and cylinder.

And the lines are the small 3/8″ O.D nylon (SeaStar 502) tubing ?

[Larry aberg]

Hi Rob the AP cannot move the rudders to the full max position

[Rob Schepis]

Larry aberg wrote:

There is a auto pilot pump installed with a course computer and goes to max during the conditions above unable to keep a course.

Does that mean that the AP pump puts the rudders hard over and the boat is not responding?

Do you have any out of water stern shots showing the hull and rudder(s) ?

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