Autopilot Upgrade

31 August 2015

Posted 08/09/2015 by Lars Stöm:

Dear Tom,

The Jefa 300 Nm drive unit should be suitable, has enough power.

Pls take a look at the table denoted “Jefa sprocket drive calculation” on their website. You have very close to 1 3/4 turns on the wheel, and the total rudder angle is 70 degrees. This means a sprocket with 15 teeth is recommended on the wheel shaft, but now there is either 33 or 48 teeth depending on the autopilot brand.

Needs to be checked if a sprocket with 15 teeth fits on the wheel shaft, if not both sprockets have to be bigger.

You could well consider not to change the present sprocket on the wheel shaft, and instead increase the sprocket size on the drive unit to provide the same 15/11 ratio as recommended by Jefa. 

Their sprockets are stainless, the recommendation is to use bronze sprockets as originally installed. You can probably have one made locally. 

A comment referring to their recommendation to test the strength of the steering gear by blocking the rudder movement – this has been done at the yard by stepping on a horizontal spoke at the wheel rim with the the wheel hard over, i.e. the quadrant against the end stop. This gives about twice the load compared to the Jefa autopilot, and it is suggested that you instead do the step test, both sides. 

Kind regards, Lars

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Posted 31/08/2015 by Tom Venator/Katface:

Looking to upgrade/replace my autopilot. I have a 24V drive motor in the steering pedestal that drives the quadrant with 5/8 chain. Have been looking at Jefa chain drive replacement. Would greatly appreciate any advice from others on what worked for them.

Best Regards, TV