Modified tiller pilot setup, any views?

[BabaYaga]

I have this question regarding the installation of a tiller pilot, which requires some background. So I will start with the essential:
Has anyone experimented with reducing the recommended distance between the rudder rotation axis and the actuation point on the tiller in order to achieve a greater degree of tiller helm (and quicker tiller movement)?

The background:
I have had an Autohelm ST4000 since 1994. This year I replaced it with a new Raymarine EV100 tiller pilot pack, which uses a tiller drive that is identical to the old one, as far as I can see.
The installation instructions for the tiller drive, regarding measurements etc, is also similar to the ST4000.
On occasions, I have experienced that the pilot, when trying to maintain the right course, struggles to do so because it hits the end stop. That is to say the rod is fully extended or retracted but this is not enough to get the boat on track. (Usually this happens when the sail balance is far from perfect and I am at the mast, trying to reef the main).
I have noticed that when the same tiller drive was used for the SPX-5 pilot (about 10 years ago or so), Raymarine in the installation instruction gave the option of reducing distance between rudder axis and actuation point from normal 457mm (18") down to 356mm (14").
I understand that doing so would not only increase the degree of helm, but also decrease the maximum force on the rudder, which I think could be acceptable.
But I would be grateful for any comments, especially from those who have tried this alteration.

 

[alahol2]

Not really directly transferable but I did mount my ST4000 closer to the stock on my Iroquois cat many years ago. The helm was very light so there was no problem with the amount of force required. I did it mainly to increase the speed of response, which it did perfectly for my situation.
If you are OK with the forces involved I don't see any reason why you shouldn't move the attachment point, the tillerpilot doesn't know where it's attached.

 

[Kelpie]

The most convenient attachment position for the tillerpilot on my Vega was closer to the rudder stock than recommended. Didn't cause any trouble, and that boat did not have a particularly light helm. So I don't think the distance is set in stone, it just depends upon the forces involved.

 

[reeac]

I have this question regarding the installation of a tiller pilot, which requires some background. So I will start with the essential:
Has anyone experimented with reducing the recommended distance between the rudder rotation axis and the actuation point on the tiller in order to achieve a greater degree of tiller helm (and quicker tiller movement)?

The background:
I have had an Autohelm ST4000 since 1994. This year I replaced it with a new Raymarine EV100 tiller pilot pack, which uses a tiller drive that is identical to the old one, as far as I can see.
The installation instructions for the tiller drive, regarding measurements etc, is also similar to the ST4000.
On occasions, I have experienced that the pilot, when trying to maintain the right course, struggles to do so because it hits the end stop. That is to say the rod is fully extended or retracted but this is not enough to get the boat on track. (Usually this happens when the sail balance is far from perfect and I am at the mast, trying to reef the main).
I have noticed that when the same tiller drive was used for the SPX-5 pilot (about 10 years ago or so), Raymarine in the installation instruction gave the option of reducing distance between rudder axis and actuation point from normal 457mm (18") down to 356mm (14").
I understand that doing so would not only increase the degree of helm, but also decrease the maximum force on the rudder, which I think could be acceptable.
But I would be grateful for any comments, especially from those who have tried this alteration.

As you say "fully extended or retracted" then your only course of action must be to increase the range of operation which means, as you've suggested, changing the position of attachment to the tiller. When we first tried our ST2000 which came with our boat we found that it wasn't able to extend far enough to turn the boat to starboard ...solution was to buy an extension for the actuating arm. I can only conclude that the previous owner had never had the device working.

 

[Iliade]

I found that reducing the rudder gain stops my TP from hitting the end stops (so often) in that situation.

 

[Tam Lin]

You can get an extension piece for the arm which might solve the problem.

 

[ghostlymoron]

The position of the actuator arm along the tiller is a compromise between speed and power. The closer to the pivot point of the rudder, the quicker the rudder will move but it will take more power to shift it due to the lack of leverage. You need sufficient leverage to move the tiller in rough conditions and you don't necessarily need to go to full lock but a small adjustment wouldn't do any harm

 

[BabaYaga]

Thanks for your input so far.
Seems like I could try and reduce the distance without any ill effects.
Regarding extension pieces for the drive, I think this is more for when the anchoring point is not at the right distance from the tiller in neutral position.
Not so on my boat, but this may change when I start experimenting.

 

[LadyInBed]

Many years back when I had an AH1000 on a 22 footer it suffered from weather helm, so I made a block with three lateral fixing holes for the AH to sit in depending on wind strength and tack. That way I kept the stock to arm length at the recommended length.

 

[William_H]

It seems to me that if the TP is running out of motion then the rudder must be at a fairly large angle when it runs out of motion. A larger rudder angle will not necessarily get your boat back on track. Indeed under some circumstances a large rudder angle especially at low boat speed can simply stop the boat with the rudder stalled as in ineffective to turn the boat.
So Op may find when he achieves more rudder deflection he still does not get boat turning response. He needs to get more speed on the boat for more control. Or lect and take up an angle to the wind conducive to more boat speed. Just a thought olewill

 

[charles_reed]

Don't know what sort of boat you have and how heavy the tiller forces are - however I shortened the distance with no ill-effects.
If the rudder has too little area ahead of the stock centre line, (ie insufficient balance area) you will get a very similar outcome as I've found on several occasions.
Why did you change from the 400ST to the later pilot?

 

[BabaYaga]

Thanks for your further comments.

According to the tiller drive manual dating from 2006, the angle of helm is 31 degrees (so 15,5 degrees to either side) with the actuation point at the normal 18" distance from the rudder stock. If this is reduced to 14", the angle of helm grows to 39 degrees. At the same time the maximum force on the tiller decreases from 84 kgf to 65 kgf.
I fully agree that boat speed is important and that no amount of helm angle will give turning response if the speed is really low. But the occasions when I have had difficulties are more related to weather helm and poor sail balance, I think. The boat is a 29'/3,6 ton long keeler. When hand steering, it can occasionally need a fairly substantial correction to get back on track, especially in gusty and bumpy conditions.
So if starting with a bit of 'natural' weather helm, this will consume some of the available 15,5 degrees mentioned above. Which is why I would perhaps be better off getting a few extra degrees of helm while losing some maximum power.

I replaced the ST4000 because of water ingress and damage to the control head/display. The old drive is kept as a spare.

 

[aquaplane]

When we first tried our ST2000 which came with our boat we found that it wasn't able to extend far enough to turn the boat to starboard ...solution was to buy an extension for the actuating arm. I can only conclude that the previous owner had never had the device working.

You may be right but my Centaur came with a ST 1000 which worked ok. When I replaced it with an ST2000+ I could only make very large turns to port, but tight ones to starboard. A new hole 4" to starboard made the ram travel about half way when the tiller was centered. Maybe your PO didn't want another hole and was happy to go in straight lines when motoring.

 

[davidmh]

If you are getting uneven turning port and starboard the most likely cause is that the anchor point for the body is not the correct distance from the centre line of the boat. All the calculations assume that when the tiller is midships the ram is half extended. That is why they provide extenders for the body mounting point. Once you have that right as others have said the nearer you get the ram to the rudder pivot the great the rudder angle changes for a set ram movement. You also need to make sure that body pivot pin is positioned so that when the rudder is midships the ram is at right angles to the boat centreline and horizontal. The feedback circuit in the electronics should quickly get to know how much to move the ram to get a required change of heading.

Regards
David H