Steering rudder


I am working on a auropilot for an 9 meter boat,
I am almost there with the bearing calculation.
Now I am working on the steering.

The Rudder is controled by an hydrolic piston witch is driven by an electrical pump.
The Pump is regulated with Relys (relais).
currently the system is coded as an on of switch (isn't tested yet) but i think the boat wil not behave accurate.

My question is,
How can I controle the pump so the boat is following the correct bearing and isn't making any big deviations on its trip?

Thanks for the help
Kind Regards

Smet victor

Greeting fellow sailor, I too have a 9m boat - an Albin Scampi 30 but from the sound of it (hydraulic controlled rudder) yours is the type that only has a cast iron mainsail!

I suggest you put a lot of thought into how the heading corrections are made. For instance if you end up 90 deg off course, you will need to make a bigger correction than if you are only 9 deg off course and the bigger the correction you need to make, the bigger and longer the rudder needs to turn by. You don't want to over compensate then have to re-compensate only to find that you've gone too far again and have to yet again re-re-compensate etc. When I took a gliding course many many years ago, that was called PIO or Pilot Induced Oscilations. Small change, check, small change, check is the way to go and you are going to have to write that into an algorithm so like I said, think hard! How would you do it manually with your hand on the tiller of wheel?

Can you make some sort of diagram of how the hydraulic rudder works at present and post it on here?

Fair winds and all that crap!


In principle the pump could be controlled with a suitable motor controller, but that depends on the details of the pump. Post all the details you can find, or better, a link to the pump data sheet or product page.

I'm looking forward to a picture of the "hydrolic piston witch".

I guess you could control the rudder by pushing and pulling the broomstick.

More seriously, what you want to do is quite complex. It will have to take into account how quickly (or slowly) the boat responds to a change in the rudder. And the possibility that its response rate is affected by the wind or water current.

Read up about PID control systems.


I’m looking forward to a picture of the “hydrolic piston witch”.


Here you go.

And there is always the hydraulic wench.

More seriously ISTR commercial systems us 2 PID.
Loop within a loop.

Controlling the pump should not be required.

Rate of rudder movement is not important.
Rate of TURN is dictated by rudder position not rate of turn of the rudder.

I guess you could control the rudder by pushing and pulling the broomstick.

Tears in my eyes dude, cant stop laughing.

I suggest you only use the broomstick when you want to Potter about.

And there is always the hydraulic wench.

I bet she does some bella tricks!

I'd suggest having a look at ArduPilot, there is a sub-mode called ArduRover which would probably work for a boat without any changes to the code. It is meant for RC vehicles and "drones". You are getting into control systems and PID loops which can be quite complex. ArduPilot has already done this, all you do is select your options, tune the PID gains and you're good to go.

thank you all for bthe info, i wil post more info soon