Homebuilt hydraulic autopilot ?

[PeterSibley]

A few years ago there was an article in a Classic Boat about an American chap who had a copy of the Carr's "Curlew" built in NZ.They built a handy hydraulic autopilot powered by the propellor .There was unfortunately not very much infromation on the various components they had assembled to create this design.Has anyone any experience of this type of device ?

[carioca1232001]

"They built a handy hydraulic autopilot powered by the propellor ."

I think you might have wanted to say 'powered by the prop shaft' or does this device obtain its power from a pick-up turbine installed in the wake ?

In principle, most autopilots are position-control servos, suitably compensated for 'hunting' and designed with fail-safe operation in mind, coupled to the tiller wheel and existing steering mechanism.

The commonly available ones are electrically-powered DC motors operating as position-control servos, but there seems to be no reason why a hydraulic motor may not be used for the same application, powered by a shaft-driven hydraulic pump or wake-driven turbine.

Just unusual !

[PeterSibley]

Unusual ,but attractive .If the 10 to 15amps x 12v required by a normal optimally sized electric autopilot could be avoided the whole proposition becomes more viable for a long distance cruiser .I don't envisage having much power generation aboard my boat ,the less the better ,so something that required only sufficient to power electronics and electrically operated hydraulic valves is attractive .The "bulk" power for pumping hydaulic fluid could come from the prop shaft....turned in turn by the propellor .:) Reasonably the faster the boat was moving the more power available .
I'm going to have to investigate this further but it seems as if a hybrid of "normal" electrically operated autopilot components and hydraulics would offer the best of both worlds .It would also be possible to use the electronics from a smaller unit .....refering to John B's thread ...without the overloading problems inherent in higher speeds .

[Hwyl]

I hate the idea. Would you want to be sailing along with the noise of the prop spinning. Every time the boat slowed down it would go of course. Modern autopilots don't use much juice if they're calibrated. If you want to really cut down on your charging (are you going to have a fridge?) get a windvane.

[John B]

Must be Charlie Beasley ,with Lark?

[Woxbox]

Any idea how much a spinning prop will slow you down? I understand it's not insignificant. A mechanical vane adds very little drag.

[carioca1232001]

Quoting Hwyl:

"Modern autopilots don't use much juice if they're calibrated."

I was trying to quantify just that, but have not got beyond the qualitative stage !

If one is zig-zagging, for whatever reason, or in a strong sea which is forcing the boat/rudder off-position, the servomotor will be working continously.

But in normal conditions and with next to 'zero error' in the servo loop, the consumption should be minimal I would have thought.

OK, the motor is rated at 10-15 Amperes at 12 V DC (nominal), but does it necessarily mean that 'steady-state' power consumption is 10 (15) Amps X 12 V DC ?

[PeterSibley]

Must be Charlie Beasley ,with Lark?

that rings a bell :).A very good looking boat ...I'll have try finding the magazine ,but as I remember ,there wasn't a lot of detail.

Carioca.....
OK, the motor is rated at 10-15 Amperes at 12 V DC (nominal), but does it necessarily mean that 'steady-state' power consumption is 10 (15) Amps X 12 V DC ?
I think so ...especially if your autopilot is working hard.It just the time that the solar panels aren't charging and you can't start the engine so you sit there watchng the charge in the batteries dropping .

Now I have to admit that I haven't sailed hard with a prop freewheeling ...how much noise does it make ? Unacceptable ?

[paladin]

referring to my other thread/remarks.....is your rudder inboard or outboard....by using a trim tab and a small servo you can generate enough power when moving with a small windpowered generator....a towed generator...or from batteries....the unit will use relatively little current if properly installed.

[Hwyl]

Even without a trim tab, if the boat is set up properly and the autopilot set to a coarse course, it won't kick in too often. People have trouble when they set their sails with weather helm or broachability and then leave "Otto" to drive.

[Paul Fitzgerald]

In a properly set up 30 footer, an Autohelm 4000 tiller pilot uses 1 amp per hour. It is rated at 4 Amps and if you get the sea cycle set up and the sails trimmed, it operates about 25% of the time.

Palladin's trim tab set up uses a lot less, but with adequate batteries and regular charging, tiller pilots are just fine for coastal cruising.

[carioca1232001]

Peter, So it is the power consumption of DC - servo-motor autopilots that is putting you off.

In your shoes, I would take the matter up with experienced mariners and equipment designers.Paladin is one. He basically reaffirms what he posted on a similar thread started by John B. Note that Hwyl also has practical experience with autopilots.

A great deal more accumulated experience with DC servo-motor autopilots for you to tap into than with one-of-a-kind hydraulic units.

But if you crave to address the subject from first principles....up to you.

[shamus]

What Paul said. Our boat came with an Autohelm ST50. Whoever programmed the 'sea state' algorithm was a genius. It soon works out what is going on and settles down to very economical steering.

[carioca1232001]

Peter, There it is ! Amazing place, the WBF !

[PeterSibley]

True ! and well said !
I'll read the above again .Paladin's idea of operating on the trim tab is great .

Paul...... In a properly set up 30 footer, an Autohelm 4000 tiller pilot uses 1 amp per hour. It is rated at 4 Amps and if you get the sea cycle set up and the sails trimmed, it operates about 25% of the time.
OK thanks ...I must admit I thought it was 4 amps continuous , a big difference .

It's readings like this ....."Autopilot selection tables based on boat length and displacement are, at best, extremely rough indicators. As a rule, it's safer to buy a size or two bigger than the minimum estimate. Although a heavy-duty actuator may suck up 12 amps or more when it's working hard, most modern autopilots offer an array of settings so the power consumption can be minimized in more benign sea conditions."
http://www.oceannavigator.com/article.php?i=&a=1183
that have confused me a bit ...mention of 12 amp draw is a worry .

Thanks for the advice gentlemen .Please educate me !:)

[MAGIC's Craig]

Peter:

For MAGIC, 25,000 lbs displacement, our Autohelm draws between 3-6 amps/hr driving a rotary motor chaindrive to our reverse rack-and-pinion Edson steering gear. Keeping the rig balanced definitely helps and the algorithms built into the "brain" are truly excellent. As alluded to, after a short bit of sensing the general sea state, it will settle down to quite a minimal amount of draw. If we are offshore sailing, we often use one of Ham Ferris' towing generators which will put out anywhere from 4 to 11+ amps/hour, depending upon speed of the boat. Penalty is approximately 1/4 knot as an average over several thousand sea miles.

Obviously not necessary for coastwise day trips but good kit for longer passages.

Cheers,

Craig Johnsen

[py]

Larger boats with hydraulic wheel steering generally have a hydraulic pump to run the autohelm. The pump is electrically operated, ie dc motor driving a hydraulic pump. I guess the idea is that driving a hydraulic pump straight off a spinning prop shaft will save some wasted energy. But a spinning prop shaft is a very inneficient way to generate power on board, whether electric or hydraulic. Its just not designed for that. A stationary prop causes much less drag, and of course a feathering/folding prop is ideal. The idea that a stationary prop causes less drag seems counter-intuitive, but apparently its true. Think of a helicopter. They can actually glide, after a fashion, on a free spinning rotor. But if the rotor is stationary, they fall out of sky like a rock.

[paladin]

helicopters don't fly...they beat the air into submission.....

[carioca1232001]

Well said !

The massive forces at play, the rotor leading-edge reversing its angle of attack every half revolution etc. make the device a marvel of engineering.

I am scared stiff to 'fly' in them, though I have on exactly 2 (two), (unforgettable) occasions !

[hancopoot]

Check out hollandwindvane.com
A professional designed stainless steel kit with over 400 units build (as Bouvaan). high quality, high performance.

Hanco

[Dan McCosh]

Conceptually, the idea of a prop-driven hydraulic motor actuating the steering, with a wind vane operating the valve is kind of interesting.

[SV Papillon]

Pretty interesting thread! I think the key would be storing the availibe energy you can create buy running something off the prop. The hydraulic pilots I have seen were dc reversible pumps that either ran a ram or motor, the the pressure static. To make it worth while you would want to have a very efficant setup, sort of how Spectra used the clark pump to utilize as much of the energy produce in a RO water maker by using the brine pressure. I woudl think something like this may work:
The key would be a gas charged hyraulic accumulator for storing the energy. If you had a hydraulic pump running off of the prop shaft constantly charging the accumulator with a electric pump that operated on a pressure switch for when there is alot of movement or the shaft is not turning very much it could work. In the simplest form the wind vane could operate a mechanical servo valve to run the ram or motor back and forth or a autopilot computer could run a electric servo valve. Since you are storing energy you only need a 1 to 1 ratio on the pump output and drive power requirments when the pilot is running nonstop, for that reason you could probably use a larger electric driven pump that would maintain constant duty if needed and a smaller prop shaft driven pump. It would take some doing to figure out exactly how much potential efficiancy there would be and how it related to hull speed in practical use. All in all it seems like it would have the potential to make a very efficiant and simple autopilot.

Jake