Auto pilot tiller arm position clarifaction

[Mg451]

I am in the brain storming process of fitting a raymarine evolution ev200 sail with type 1 linear drive. When designing the tiller arm. ( which will clamp to bronze rudder stock) i was asuming the rudder would be straight back and the tiller arm would attatch to the rudder shaft facing straight fwd. I would mount the drive at a 90degree intersection attatch it to the tiller am with the drive at midstroke. Rudder stops would stop it from going to far.

Im reading steve de antonios booklet on systems steering part 1 me hanical systems. He says;

Additionally, the geometry between
the tiller arm and the ram must be cor-
rect to derive the greatest mechanical
advantage when it’s needed most—
when the rudder is moved away from
amidships; while it’s dead ahead, the
least effort is required. Ideally, and
contrary to popular belief, the ram
should not be positioned at 90° to the
tiller arm and vessel centerline (assum-
ing, in this example, that the tiller is
fore-and-aft when the rudder is fore-
and-aft) when the rudder is straight
ahead; rather, it should be at 90° when
the rudder is over to some degree
(steering and autopilot manufacturers
typically specify the degree) in either
direction, thereby enabling the ram to
impart greater force when it’s needed
most. This often means the ram, if
installed athwartships, must be posi-
tioned farther aft.

If i understand this is he saying its best NOT to do it in the orientation i described? Having trouble understanding this...

[DougR]

Steve is correct. If you download and read most autopilot installation manuals for linear drives, whether electro/mechanical or hydraulic, they recommend the angle between the tiller arm and the linear drive be less than 90* when rudder and tiller arm are straight ahead.

[Mg451]

Let me reread the raymarine literature. Im having trouble getting my head around this for some reason. The tiller arm does go straight fwd. The drive isnt at a 90 its slightly aft. I see that. But i dont understand how this effects the rams strength. The rams strength is consistent through its whole stroke however the rudder will require the most strength when its hard over either way and the Least when midship. Im having trouble understanding how this helps the rams effect ?

[Rucksta]

When I look at the geometry, setting the tiller arm at other than 90 degrees gives a mechanical advantage in one direction and a dis-advantage in the other direction.

What am I missing?

[thinwater]

Originally Posted by Rucksta

When I look at the geometry, setting the tiller arm at other than 90 degrees gives a mechanical advantage in one direction and a dis-advantage in the other direction.

What am I missing?

Draw a picture, showing ahead and 30 degrees each way. You will see. It will be straight-across on both tacks, with the helm over at some angle.

[thinwater]

Raymarine specifies 90 degrees (from manual).

https://www.manualslib.com/manual/13...?page=9#manual

[Mg451]

I think i understand if the tiller arm is fwd and if you were to place the ram at 90degre angle when the helms over each way the ram would be out of that 90. So if you back it up making it out of 90 when its fwd but it would go back into 90 when fully extended or retracted..Sorry i cant eloquently explain that. But i got what you mean now.

[Mg451]

So it makes sense now....but its not how raymarine install says. Wonder why?

[Mg451]

"Must be at 90 degree when admidships"

[goboatingnow]

Jefa, which I have installed , make it clear that the ld100 should be at 90 degrees at amidships https://www.jefa.com/ftp/steering/in...drive-v1.2.pdf

If jefa says it’s the way , that’s way good enough for me

It makes perfect logical sense. Autopilots typical spend most of there time , at +-10 degrees , the loss of mechanical advantage is trivial and most linear arms have way more power then needed anyway.

90 degrees it is.

[Rucksta]

Originally Posted by thinwater

Draw a picture, showing ahead and 30 degrees each way. You will see. It will be straight-across on both tacks, with the helm over at some angle.

Have drawn a few pictures and just don't get it.
I still come up with a mechanical disadvantage on one tack.
A sure sign I'm still thinking inside the box.
Perhaps you can draw the correct diagram and enlighten us all?

[Mg451]

Blue is rudeer green is the ram 1st pic would be rudder straight ahead ram slightly out of 90 and behind it..now if you extend the ram (hard over) its back into 90 . On both tacks

[Hermia II]

The RAM must engage at 90° straight ahead, the ram at mid stroke (this geometry can be rotated around the rudder axle of course). The leaver will decrease when it starts steering, but it must be equal both ways. If you set it at 100° the leaver will be at the longest at 10° but not the same at -10°, so it is not symmetrical, so that is not the right way.

[skipmac]

Originally Posted by Mg451

Rudder stops would stop it from going to far.

If I understand your meaning here, you would use the physical limiters on the quadrant to prevent the drive from pushing the rudder too far port or stbd? If so I don't believe this is recommended. The range of motion of the linear drive and the length of the quadrant should be such that the drive cannot push the system as far as the physical stops. To allow the drive to push until the quadrant hits the limiters could damage the drive or the tiller arm or something in the system.

[Cheechako]

I think what he is saying in a nutshell is it requires more force to turn the rudder once it not at center. So if you can mount the mechanism so it applies force at 90 degrees to the under deck "tiller" , with it somewhere off center that is better.

In the real world, not sure I understand how that will work for both sides of center though... without obstructions?