Can I use a wheel drive autopilot on a 50ft, 20 ton yacht with hydraulic steering?

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fuss

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Wheel drive autopilots seem to be for smaller yachts of around 8 tons max. My hydraulic steering is finger light with 3 turns from lock to lock. My autopilot is an expensive constant running pump that consumes 8 amps at 24v for the whole time it is running. I cannot see why I could not fit a wheel drive unit that consumes a lot less amps and also should work just as well as the main unit.
Has anyone tried this?
 
fuss said:
Wheel drive autopilots seem to be for smaller yachts of around 8 tons max. My hydraulic steering is finger light with 3 turns from lock to lock. My autopilot is an expensive constant running pump that consumes 8 amps at 24v for the whole time it is running. I cannot see why I could not fit a wheel drive unit that consumes a lot less amps and also should work just as well as the main unit.
Has anyone tried this?
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No, I haven't tried it. If the steering is as light as you say, then obviously there is no reason why you should not do that. If the load becomes greater in heavy weather you could always switch back to the hydraulic.

Another way might be to fit an electric linear actuator? Or a wind vane?
 
The problem with a wheel pilot is not the load on the wheel, but the lack of positional feedback from the rudder- hydraulic systems will inevitably not return to exactly the same position of wheel relative to the rudder over a period of use, because of internal leakage past the seals.
As the wheel position / rudder position is not consistant, the autopilot becomes confused.
If you have an autopilot system with a rudder reference unit incorporated (positioned at the rudder quadrant), you might be able to have it feed a suitable geared electric motor coupled to the steering wheel, but it may need a lot of tinkering to get it right.
 
NorthUp said:
The problem with a wheel pilot is not the load on the wheel, but the lack of positional feedback from the rudder- hydraulic systems will inevitably not return to exactly the same position of wheel relative to the rudder over a period of use, because of internal leakage past the seals.
As the wheel position / rudder position is not consistant, the autopilot becomes confused.
If you have an autopilot system with a rudder reference unit incorporated (positioned at the rudder quadrant), you might be able to have it feed a suitable geared electric motor coupled to the steering wheel, but it may need a lot of tinkering to get it right.
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The raymarine smartpilot x-5 requires no rudder reference, this is the latest version from raymarine and the first that requires no rudder reference. With autolearn for adapting different sea conditions I cant see why it would not work on larger boats as long as the steering is light. However raymarine specifically state a laden displacement of up to 7500kg.
 
The displacement limit may not onlt be there with regards to the force required to turn the wheel, but also the 'steerability' of the vessel. typically as they get bigger they get les responsive, as an extreme example I suspect that the wheel is easy to turn on an oil tanker, but I highly doubt a Raymarine autohlme will keep it on course considering it takes so long to respond and has a 3 mile turning circle. Ok you are no where near that, but their must be limits as to what the control algorythm is designed to do / respond to.

Ants
 
NorthUp said:
The problem with a wheel pilot is not the load on the wheel, but the lack of positional feedback from the rudder- hydraulic systems will inevitably not return to exactly the same position of wheel relative to the rudder over a period of use, because of internal leakage past the seals.
As the wheel position / rudder position is not consistant, the autopilot becomes confused.
If you have an autopilot system with a rudder reference unit incorporated (positioned at the rudder quadrant), you might be able to have it feed a suitable geared electric motor coupled to the steering wheel, but it may need a lot of tinkering to get it right.
Click to expand...

Understand what you are saying but I found that a wheel pilot on a prout cat with hydraulic steering worked OK despite the steering wheel drift you described.

The reason for the weight limit put against pilots is that bigger heavier boats generate more rudder load and that either means more load at the wheel or a lower gearing of the steering and a similar load. As it happens I had to change the gearing on the hydraulics of the Prout to get round the problem that the autopilot was not happy with 3 or more turns lock to lock. The boat didnt react fast enough for the electronics and the system shouted "time out" so to speak.
 
Jason -- As a (one-time) Instrumentation and Controls engineer, that's what I would expect. The OP is only suggesting that he adds the new wheel pilot, not that he removes his hydraulic system. If it will work for him most of the time then he is ahead. He can always turn on the big hydraulic system when things get more difficult. Sounds like a good idea to me.
 
Lemain said:
Jason -- As a (one-time) Instrumentation and Controls engineer, that's what I would expect. The OP is only suggesting that he adds the new wheel pilot, not that he removes his hydraulic system. If it will work for him most of the time then he is ahead. He can always turn on the big hydraulic system when things get more difficult. Sounds like a good idea to me.
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Thats true, my boat is very responsive, has finger light steering in almost all weather as its hydraulic, has 3 turns lock to lock just like many cable steering systems, the latest raymarine wheel pilot requires no rudder reference. I cannot see why this won't work and save me amps at the same time.
 
I agree with Lemain - it will most likely work a part of the time. The issues you need to check are the gearing of the steering - turns from lock to lock and is this compatible with the autopilot max turns. Also the diameter of your wheel - your "finger light" might be on a 12 inch dia wheel or a 48 inch dia one, a variation of 4 in the load that an autpilot would see with its standard pulley size. And then there is the issue of hull balance and sail adjustment. A small autopilot will control a big heavy boat that has a slim and well shaped hull but will struggle with a smaller broad sterned AWB when heeled. Finally there is the issue oof hydraulic slip - ie how much you can slowly move the wheel when the steering is on full lock due to leakage at the seals. Too much of this will really bu**er up the autohelm which expects the rudder to be at the same place when the wheel is.

The weight limits manufacturers put on the autohelms are not to play silly games but as a general guide for the average boat. If you chose to go outside those limits then you are on your own.

FWIW the problem I got with the Prout was reaction time. The autopilot didnt like 3 turns lock to lock at all - it wanted the 1.5 which is more typical of rod systems. Combine that with a boat which has exceptional directional stability (ie slow to turn) and I got problems. Hence the need to change the gearing of the steering but at 33 ft overall, this was still lightish when I got it to 1.5 turns.
 
NorthUp said:
but the lack of positional feedback from the rudder- hydraulic systems will inevitably not return to exactly the same position of wheel relative to the rudder over a period of use, because of internal leakage past the seals.
.
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My old Autohem 800 might initially use return to centre however it overrides this if any other force such as wind and tide comes into play and estasblishes a virtual centre. I am sure that the modern Autohelms will do this far more efficiently which means that there should be no problem with the autohelm as it automatiaccl centres around the wheel position that maintains the set course. This could be a beam wind or non centred wheel. It ain t going to know the dfference. Double check with te makers but I am sure this will be the case from what I have seen with mine.
 
Bilgediver:
very good points you make, and as I havn't tried it I won't argue!
The rudder reference unit also limits the max amount of helm the autopilot will apply, to stop it stalling the motor 'hard over', or the boat taking large swings one way or the other.

Back to the OP- to reduce current consumption- would it be possible to source a reversing electro-hydraulic motor to drive your existing system?
That would only run when a helm movement was needed, and if your craft is reasonably stable steering wise may be more energy efficient.
Usually they are fitted to smaller systems than on your size of boat, because their output is more limited, and are not ideal if they have to work hard constantly changing direction.
Your existing electronics probably have this as an option in a sub menu deep in dealer mode.
All depends on the relative size of the hydraulic ram(s) at the quadrant, and output of the pump- too small and it will hunt for the correct course, taking ever bigger swings until the electronics cry stop.
 
Bilgediver said:
My old Autohem 800 might initially use return to centre however it overrides this if any other force such as wind and tide comes into play and estasblishes a virtual centre. I am sure that the modern Autohelms will do this far more efficiently which means that there should be no problem with the autohelm as it automatiaccl centres around the wheel position that maintains the set course. This could be a beam wind or non centred wheel. It ain t going to know the dfference. Double check with te makers but I am sure this will be the case from what I have seen with mine.
Click to expand...

So did my AH800 and my ST2000+ You don't need a rudder indicator for the system to work, as you say.
 
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