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Old 08-12-2016, 05:36 AM   #1
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Powering autopilot from main hydraulic pump

For a boat equipped with an engine-driven hydraulic pump for the windlass and thruster, I'm questioning whether it is good practice to run the autopilot from this supply.

Main hydraulic pumps are rated in many gallons per minute and need the 12v clutch to be activated. However, when underway, the only load would be the autopilot which typically would require a fraction of that output.

So in essence there is wear and tear being put on the hydraulic pump when it is being utilized for perhaps only a few percent of its rated output. For a vessel that undertakes long cruises this would seem like a waste that will lead to expensive repairs when that pump wears out early in its life.

So it would seem that even having an engine driven pump that it would be better to still utilize the typical 12v hydraulic pump that powers most autopilots. I suppose that with just a few valves that the main pump could be a backup source of pressurized oil.

Thoughts???
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Old 08-12-2016, 06:25 AM   #2
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Our boat has a hyd pump , similar to the PS pump in most cars , just bigger, one belt..

It operates the helm which has a fine wooden wheel, which could just as easily be a door knob.Its just a valve.

The Robertson AP uses 2 Vickers 12v DC solenoid valves to steer .

At 1/2 an amp operating the Robertson will not be overworked.

As a bonus the pump is able to operate out Hyd capstan , cooling is handled by simply leaving the hyd lines in the bilge water.

As a back up we have a 12V hyd power pack (as used by some AP) that should have little problems should the hyd power belt brake .

Probably would bring the anchor up too as the engine only requires a slow idle .

"So in essence there is wear and tear being put on the hydraulic pump when it is being utilized for perhaps only a few percent of its rated output"

Most have an internal pressure regulation so little power will be used.

Hyd has a long life , replaced your car PS pump lately?
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Old 08-12-2016, 09:09 AM   #3
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Quote:
Originally Posted by FF View Post
Our boat has a hyd pump , similar to the PS pump in most cars , just bigger, one belt..

It operates the helm which has a fine wooden wheel, which could just as easily be a door knob.Its just a valve.

The Robertson AP uses 2 Vickers 12v DC solenoid valves to steer .

At 1/2 an amp operating the Robertson will not be overworked.

As a bonus the pump is able to operate out Hyd capstan , cooling is handled by simply leaving the hyd lines in the bilge water.

As a back up we have a 12V hyd power pack (as used by some AP) that should have little problems should the hyd power belt brake .

Probably would bring the anchor up too as the engine only requires a slow idle .

"So in essence there is wear and tear being put on the hydraulic pump when it is being utilized for perhaps only a few percent of its rated output"

Most have an internal pressure regulation so little power will be used.

Hyd has a long life , replaced your car PS pump lately?
it could be me but this sounds so wrong... I NEVER want a boat with enough water in the bilge to act as a cooling reservoir..

HOLLYWOOD

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Old 08-12-2016, 10:37 AM   #4
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I think if you spec a pump and drive system suitable for a thruster at idle rpm, it will be way overkill for running at cruise rpm and just driving an AP. Not that it would hurt the hydraulics, that stuff is really dependable, but the parasitic hp consumed would be just a waste of fuel.

I would keep steering and thruster system separate from steering. One option is for thruster to be driven by genset engine, this has the advantage of being constant rpm. You would have to start gen for maneuvering, but that is not a big deal.

If using a four hose steering system, you can put a little pump on your engine or gear then use it for steering and stabilizers if installed.

Another boat I set up we installed a dc drive hyd power pack for the steering. That worked really well. Can drive off either engine 24v alt, or gen via 24v charger to the 24v banks. The engines and gears did not have a convenient pump pad and owner wanted power steering.

Lots of options here. For steering you can go manual hydraulic with elec ap pump, electric over hyd power steering with elec ap pump, power hydraulic rudder cylinder with elec ap pump, four hose power hydraulic with solenoid valve ap. And the hyd power source can be elec or engine driven pump.

It depends on the size of the boat and expected duty cycle and equipment list.

But I would keep thruster and winch away from steering. Very different duty cycles, hard to make them compatible.

Also it is good to consider main engine and steering SACRED. Minimize connections with non vital equipment. You don't want a failure in your non vital stuff to take out sacred stuff.

One advantage of four hose, AKA "forklift steering" is all the stuff can be spec'd from industrial equipment at reasonable cost.
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Old 08-13-2016, 08:41 AM   #5
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For the larger boats , using the "get home" engine that may lie idle from season to season is even better than using the noisemaker, for a thruster.

Diesels seldom wear out , but are easy to kill,

Just ignore it.
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Old 08-13-2016, 09:49 AM   #6
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Quote:
Originally Posted by makobuilders View Post
For a boat equipped with an engine-driven hydraulic pump for the windlass and thruster, I'm questioning whether it is good practice to run the autopilot from this supply.

Main hydraulic pumps are rated in many gallons per minute and need the 12v clutch to be activated. However, when underway, the only load would be the autopilot which typically would require a fraction of that output.

So in essence there is wear and tear being put on the hydraulic pump when it is being utilized for perhaps only a few percent of its rated output. For a vessel that undertakes long cruises this would seem like a waste that will lead to expensive repairs when that pump wears out early in its life.

So it would seem that even having an engine driven pump that it would be better to still utilize the typical 12v hydraulic pump that powers most autopilots. I suppose that with just a few valves that the main pump could be a backup source of pressurized oil.

Thoughts???
Just install the recommended pump for your autopilot. And leave the PTO pump for the thruster/windlasses.

That is the way it's most commonly done. And it works just fine.
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