Rudder torque

[Columbus]

I have a tayana 55 from 1985 - the FreeSpirit. As with all the systems I'm reworking the hydraulic steering system and auto pilot.
The steering rams have a torque rating - to match or exceed the torque rating for the rudder.
This number is relevant to both the rating of the ram and the specification of an auto pilot for it.

Not finding any info on specs for the rudder for the boat.

I have found a calculator for rudder torque -
C = S x [ (0.4 Lg) – Lc ] x V² x K.

The is an online calculator here:
https://www.ls-france.com/en/power-a...lation-assist/

Does anyone have experience in these calculations?

Thanks in advance! James

[Bill O]

James,
Best and simplest thing to do would be to measure your existing rudder to do the calculations. Since it's a skeg held rudder, there will not be much leading edge to measure, so you will only need the height and width measurements to do the calculations.

Besides torque, would also size up the pump for a rudder speed to match the hard over times listed in your AP set up.

Another criteria for us was a quiet pump since ours is mounted under the cabin sole in the aft cabin. We had read that the Simrad pump was quite loud, and some people said it sounded like copulating cats!(maybe they had air in their pump?) We went with an Accu-Steer (Kobelt) pump after we were on an Amel with this pump installed. We mounted the pump bracket on pillow blocks and it is whisper quiet.

[Rucksta]

Or you could attach a torque wrench to the rudder post (emergency tiller?)and measure how much effort is required to steer