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Old 16-09-2012, 02:58   #1
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Autopilot install, why is it so?

Hi there

Im about to install my autopilot on my tiller, its a autohelm st4000.

simple question, it says that the unit needs to be installed 600++ mm off the centerline of the rudder understandable so that its in the middle of the rams range of movement.

then it says that it needs to be installed 420 mm from the center of the rudder stock? why?.

ideally i would like to install it a little short of this, maybe around 300++ mm, and the units well overpowered for my steel yacht of 28 ft 5.5 ton so the ram should be able to move my rudder under all circumstances

who can answer this with a logical reason?

thanks in advance

Matthew
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Old 16-09-2012, 03:33   #2
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Re: Autopilot install, why is it so?

Quote:
Originally Posted by resilientg View Post
Hi there

Im about to install my autopilot on my tiller, its a autohelm st4000.

simple question, it says that the unit needs to be installed 600++ mm off the centerline of the rudder understandable so that its in the middle of the rams range of movement.

then it says that it needs to be installed 420 mm from the center of the rudder stock? why?.

ideally i would like to install it a little short of this, maybe around 300++ mm, and the units well overpowered for my steel yacht of 28 ft 5.5 ton so the ram should be able to move my rudder under all circumstances

who can answer this with a logical reason?

thanks in advance

Matthew
The 420, in combination with the 600, determines the arc of travel thru which your rudder will travel. All A/P installs have 2 control distances.
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Old 16-09-2012, 04:17   #3
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Re: Autopilot install, why is it so?

Mathew,
The distance from the rudder post to the attachment point on the tiller determines the range of movement of the tiller under AP control, but also the amount of force require to move the tiller when under way.
Moving the attachment point 1/4 of the distance from the recommend point on the tiller toward the rudder post will increase the force required to steer the boat. Whether the ST4000 has enough power for your desired attachment point will depend on the type of rudder and conditions under which you use the AP in addition to the displacement of your vessel. If you have a balanced or partially balanced rudder there may be no problem. If you have a barn door rudder hung on the keel or a skeg it may not work well.
One of the good things about a tiller AP is that it is not a big deal to change the installation if it doesn't work out.

John
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Old 16-09-2012, 05:55   #4
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Re: Autopilot install, why is it so?

and ... to follow up on the above ... if you install it further along the rudder, the turning arc is smaller.

Which is a little bit of an issue if you plan to use the auto-tack function.

I own a ST4000, and it is installed 600mm from the rudder stock ... and if I use the autotack function it doesn't turn the rudder far enough, and the boat ends up in irons.

I'm guessing the previous owner did this on purpose as the ST4000 is a little underspec for my yacht. Seems to work fine though.
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