Chain or Linear Autopilot?

[Tim Good]

What is better and why? A chain drive unit turning the wheel or a direct linear drive onto the rudder quadrant?

My thoughts. The AP on the chain would get better mechanical advantage of the wheel system and maybe use less power but if the wheel mechanism is damaged in any part then you loose the ability to use AP.

I'm asking this as I currently have a chain drive unit installed inside my Whitlock pedestal on an old Whitlock Mamba steering gearbox. It looks like it has packed in. Someone else with the same boat has a linear drive directly onto the quadrant on top of the rudder stock. The later seems to me like a good idea. Thoughts?

 

[sailorman]

What is better and why? A chain drive unit turning the wheel or a direct linear drive onto the rudder quadrant?

My thoughts. The AP on the chain would get better mechanical advantage of the wheel system and maybe use less power but if the wheel mechanism is damaged in any part then you loose the ability to use AP.

I'm asking this as I currently have a chain drive unit installed inside my Whitlock pedestal on an old Whitlock Mamba steering gearbox. It looks like it has packed in. Someone else with the same boat has a linear drive directly onto the quadrant on top of the rudder stock. The later seems to me like a good idea. Thoughts?

a ram on the quadrant gives you a safe back-up steering system
if an indirect system fails you are stuffed, no steering at all

 

[westhinder]

No experience with a chain drive, I'm afraid. We have the ram on the quadrant and are very pleased with it. No drag whatsoever on the wheel when the autopilot is not in use and the pilot is reliable and very quick in responding. It's a Robertson system

 

[RichardS]

a ram on the quadrant gives you a safe back-up steering system
if an indirect system fails you are stuffed, no steering at all

What about the usual emergency steering direct into the top of the rudder stock?

Richard

 

[Yngmar]

Talked to a chap on an Elan whose ram autopilot had failed during a channel crossing. The sea was a bit unpleasant and the ram in a difficult to access location, so he just hand steered the rest of the way.

Upon arrival in port, he poked his head in there only to find the ram had popped off the quadrant and been laying (and sliding) on top of it. If it had wedged itself in there and jammed the quadrant, he'd have lost all steering.

 

[Tranona]

As ever, there are pros and cons. Lewmar offer the chain drive system and it was popular in the early days of autopilots before Autohelm/Raymarine entered the market with their systems which were either belt drive on the wheel or ram on the quadrant. Chain drive systems were generally more powerful and fitted to larger heavier boats. They are simple and reliable, but do rely on the wire or rod drive to the rudder. In some applications they are easier to install as they do not need modifications to the boat to provide a secure mounting point for the drive, nor any modification to the quadrant.

If it is working there is no reason to change it, and some might argue that it is a much better engineered system than the cheaper ram.

Edit Just noticed you seem to be saying it has stopped working (originally I thought packed in meant it was installed in a small space!). You will need a big ram to drive your boat and will probably need to build a substantial platform to mount it on plus an actuator arm on the rudder stock (rather than drilling a hole in the quadrant). Expensive job and you may find getting the motor overhauled a better bet. They are relatively simple devices, but it is also worth having the electronics tested before taking the drive apart.

 

[lpdsn]

a ram on the quadrant gives you a safe back-up steering system
if an indirect system fails you are stuffed, no steering at all

+1. An awful lot easier to steer home pressing the buttons than to try to get an emergency tiller set up and working properly.

Talked to a chap on an Elan whose ram autopilot had failed during a channel crossing. The sea was a bit unpleasant and the ram in a difficult to access location, so he just hand steered the rest of the way.

Upon arrival in port, he poked his head in there only to find the ram had popped off the quadrant and been laying (and sliding) on top of it. If it had wedged itself in there and jammed the quadrant, he'd have lost all steering.

Mine has a split pin through a hole in the peg to stop it popping off.

 

[sailorman]

What about the usual emergency steering direct into the top of the rudder stock?

Richard

I also have that, you wouldnt want to steer far with that in a breeze

 

[aluijten]

As ever, there are pros and cons. Lewmar offer the chain drive system and it was popular in the early days of autopilots before Autohelm/Raymarine entered the market with their systems which were either belt drive on the wheel or ram on the quadrant. Chain drive systems were generally more powerful and fitted to larger heavier boats. They are simple and reliable, but do rely on the wire or rod drive to the rudder. In some applications they are easier to install as they do not need modifications to the boat to provide a secure mounting point for the drive, nor any modification to the quadrant.

There is an even more reliable system that does not have the problem of making a linear movement from a rotary movement. It uses a system of two tillers (one one the servo and one on the rudder-stock) connected by a draglink. This way you only have rotary bearings that are much more reliable that any linear bearing. Both Lewmar and Jefa supply these servos.

See:
http://www.jefa.com/steering/products/drives/direct-dd1.htm

 

[Koeketiene]

a ram on the quadrant gives you a safe back-up steering system
if an indirect system fails you are stuffed, no steering at all

+1

 

[geem]

We have a super powerful rotary drive onto our Whitlock shaft drive steering system. The rotary drive sits in the engine room where access is easy. Having any direct drive onto the quadrant would be a nightmare for access. Failure of the shaft drive system is extremely unlikely if you are familiar with these systems but not out of the question. The emergency tiller plugs in to the rudder stock with a long tiller. Not ideal but good enough to get you home. The boat will steer it's self when balanced properly so no concerns here. Having seen how many shaft drive units get stripped off boats in Horta (after a bumpy Atlantic crossing) for repair I would not choose to go that route over powerful rotary drive.

 

[nauticalnomad]

I have just bought a Jefa linear drive unit that im installing ontop of the rudder stock which was/is my emergency tiller point.
I was worried about putting it on the quadrant and the force breaking the quadrant. (I have seen it happen)
If I need to access my emergency tiller ill have to pop off the bracket to use it.

 

[lpdsn]

I was worried about putting it on the quadrant and the force breaking the quadrant. (I have seen it happen)

Happened to me. The cause was a badly fitted fitting where they'd drilled holes in a cast aluminium quadrant. I bought a Jefa fabricated Duralium quadrant with the ram attachment point welded on. Not cheap, but one of those things where the quality is worth the extra price.

 

[GrahamM376]

My type 1 linear drive is mounted on a pin which in turn is mounted on a thick stainless plate cut to the shape of the quadrant to which it is bolted at various points to spread the load over the whole quadrant.

As the drive is the later model with metal gears, no problems in many years and thousands of miles. I like the back-up steering possibility if a cable breaks.

 

[KellysEye]

>I'm asking this as I currently have a chain drive unit installed inside my Whitlock pedestal on an old Whitlock Mamba steering gearbox.

We had one of those and it's the best steering available, I would have it repaired, we also had a chain driven autopilot.

 

[RAI]

What is better and why? A chain drive unit turning the wheel or a direct linear drive onto the rudder quadrant?

My thoughts. The AP on the chain would get better mechanical advantage of the wheel system and maybe use less power but if the wheel mechanism is damaged in any part then you loose the ability to use AP.

I'm asking this as I currently have a chain drive unit installed inside my Whitlock pedestal on an old Whitlock Mamba steering gearbox. It looks like it has packed in. Someone else with the same boat has a linear drive directly onto the quadrant on top of the rudder stock. The later seems to me like a good idea. Thoughts?

Are you talking about electric or hydraulic drive? I can't address hydraulic. I have a Raymarine electric chain drive onto a Whitlock system. It works well but its predecessor's motor burnt out (after 35 years). The old one had a mechanical engagement system. The new one uses a magnet clutch, which alone take 2 amps, a bit of an excess drain. I fitted the Raymarine replacement because it was easy to do, compared to going hydraulic or trusting an electric ram (which I wouldn't).