Downsizing hydraulic cylinder 1

[marinovich.91]

Hi to everyone, first I wil try to put here my current system, then what I would try to do and then couple of questions. This may be a big thread but my apopogies.

The current problem on my sailboat is that somebody before I bought it had putted hyrdaulic steering on 31 foot boat, and made couple of mistakes along the way.

So courrent setup is that i have:
28cc/turn steering helm pum connected to 70cm diameter steering wheel - axial piston pump
168cc capacity steering hydraulic cylnder
System max press 70bar

This gives me 6 turns from end to end, and main problem is that I dont feel the rudder at all(no feedback). I have been googling it a lot and found that there is couple of solutions.

Before I continiue I must mention that I have raymarine EV100 Autopilot connceted to my steering wheel over Autopilot wheel attached to it(with small electromotor)


So to get any feedback from rudder I found that I need to remove checkball’s from nonreturn valve system on helm pump(80% sure). So fluid from my steering cylnder can influence steering wheel.


At current system I dont need use any effort to turn the wheel and when there is rough sea, sailboat is behaveing like local drunk, since I cant chatch the boat>>There is no feeling and 6. turns from end to end.
Manovering is story for its own.

Solution for this is downsizing hydraulic cylinder or buying bigger capacity pump. Since I dont have space, and hy. cylnder is cheaper to change I decided to change the cylnder.

The main problem arise when I contacted Seastar tech. support about it.
He told me downsizeing the cylnder effort on steering wheel incrises a lot. (a lot is the main problem).

Recently I calculated my rudder torque by calculateing area an running it in calculator and got 6kg/m. Pictures attached, Calculator web site is on this link..

Calculator gave me:
Force of 210
Rudder torque of 6kg/m

I am not sure since there isnt any units; what this should mean

Solution 1.
I would like to go for 69cm3 (2.5 turns) capacity of hydraulic cylnder but I dont know if my autopilot will be able to handle it becouse friction of fluids and pump. As well max torque of cylnder is 32 kg/m but output force is 170kg.


Solution 2.
Another option is to go for 84cm3 (3 turns) capacity of hydraulic cylnder but I dont know if my autopilot will be able to handle it becouse friction of fluids and pump. As well max torque of cylnder is 58 kg/m but output force is 387 kg.

Lady in Hydrodrive told me:
On application 28cc pump and 84cm3 cylinder, on shaft pump, to reach the max pressure, needed a torque of 42 Nm on pump shaft.What does this mean if my max torque from rudder is 6kg/m?

But I want the feedback as well.

The main question is how to calculate how much stiff my steering wheel is going to be, since I want it to be just on border so my autopilot can handle it, to have feedback, as little as possible turns and normal effort steering.

Thank you for your Help and time

https://files.engineering.com/getfi...089-414b1d2717ea&file=Proracun_za_kormilo.jpg

https://files.engineering.com/getfi...d5-485f-a554-5c58dd92e1f9&file=Hidraulika.jpg

 

[akkamaan]

Just to confirm. Is this power needed on pump shaft, not on 1m, on ideal system offcourse?

Power is never related to the diameter of the wheel so it is on the shaft
Formula from Bosch (Rexroth)

 

[hydtools]

To clarify the example, etamh = 1.

Ted

 

[hydtools]

Marinovich.91, you have not yet determined how much force is required to push against the rudder torque. You, therefore, do not know how much hydraulic pressure is required to generate that force.

Ted

 

[hydtools]

This is informative.

https://www.sbmar.com/articles/marine-hydraulic-steering-systems/

Ted

 

[73lafuite]

Hello,
If the axis of rotation of the rudder is that of the axis of thrust of the water there is no feedback. You should try to put pressure gauges between the valves and the orifices of the jack to find out more.
cordially

 

[zeusfaber]

On low speeds ruder torque gets smaller so there isn any force on cylnder and thus no feedback.

There are actually two elements to rudder torque.

The first one is the hydrodynamic load resulting from the rudder working to turn the boat. This is surprisingly complicated, with different types of ship generating their peak torque at different stages of the steering manoeuvre but - as you have pointed out - this load generally increases with speed.

The other one - and this is the one most likely to break your wrist - is what happens when a big wave hits you from behind and slaps the rudder hard-over. You may not see this sort of event every day, but it's what did for Amoco Cadiz, and it's the reason we have crossline reliefs set at 200 bar on ships whose hydrodynamic loads put little more than 40 bar into the hydraulics.

A.

 

[hydtools]

There is something of a balancing rudder surface to reduce the resultant steering load.

Ted

 

[hydtools]

Did you find that the helm torque = rudder torque x (35/360) x pump displacement/steering cylinder displacement ?

Ted