Electro-hydraulic systems?

[Alaskaflyer]

Are yachts in the typical size discussed around here ever found to be using an electric motor to run a hydraulic pump for bow thruster, windlass, maybe davit/crane? With the electric motor powered by an existing ship’s generator in the 9-14kw range?

The examples I’ve seen for a trawler yacht with hydraulic systems have the pump either coupled to the main - which can sometimes bring problems with insufficient power delivered at the idle speed necessary for close quarters maneuvering - or to a separate aux. engine, which may not be practical. So if one had an existing main-driven hydraulic pump - say, belt driven - and wanted to convert the system to be driven by an electric motor instead…?

 

[guy with a boat]

Seems like you would have to run a gen to power the electric motor, so you might as well have a PTO on the gen. If powering the electric to PTO, maybe more efficient to stay with electric thrusters. I’m just having a hard time finding an advantage to what you are suggesting.

 

[O C Diver]

There are some Krogens and I believe Nordhavns with hydraulic pumps on their generators. Doesn't seem to make much sense generating electricity to convert it to hydraulics. The only possible advantage I see is keep all the hydraulics for windlass and bow thruster confined to the bow compartment.

Ted

 

[Alaskaflyer]

Seems like you would have to run a gen to power the electric motor, so you might as well have a PTO on the gen. If powering the electric to PTO, maybe more efficient to stay with electric thrusters. I’m just having a hard time finding an advantage to what you are suggesting.

The theoretical boat is already equipped with hydraulic appliances (insufficiently) powered from the main engine while idling.

Would marine gensets of this size have the capability for a hydraulic system to be coupled to the engine block in addition to the AC alternator?

 

[Alaskaflyer]

There are some Krogens and I believe Nordhavns with hydraulic pumps on their generators. Doesn't seem to make much sense generating electricity to convert it to hydraulics. The only possible advantage I see is keep all the hydraulics for windlass and bow thruster confided to the bow compartment.

Ted

Well that’s an interesting thought but then you’d have the voltage drop from placing the motor that far from the generator.

 

[Ventana]

We have a Krogen 42 with a hydraulic pump on a PTO from the genset, used for a get-home drive system on the main prop shaft. I had considered switching the windlass and thruster to hydraulic since the system is already in place, but decided against it. Doing so would make us completely dependent on the genset for starting and ending most trips. As it is now, I have three sources of DC power for the windlass and thruster and I like the redundancy.

 

[Alaskaflyer]

We have a Krogen 42 with a hydraulic pump on a PTO from the genset, used for a get-home drive system on the main prop shaft. I had considered switching the windlass and thruster to hydraulic since the system is already in place, but decided against it. Doing so would make us completely dependent on the genset for starting and ending most trips. As it is now, I have three sources of DC power for the windlass and thruster and I like the redundancy.

Thanks. May I ask what your genset combo is? Does it function with a clutch allowing only one or the other to function or is it a PTO allowing for AC generation while using the hydraulic system?

In the back of my mind is a possible later addition of a get-home system able to be coupled to the main shaft as in your example, which of course would only work if I relied on something else besides the main to run the hydraulics.

 

[FF]

The biggest advantage would be in an overload situation. A an electric windlass , would pop a CB, blow a fuse , or LUCAS , let all the white smoke out.

The hyd unit will just stop no harm done.

A hyd pump pad on both the main and gen set would be ideal for an offshore cruiser.

All the usual heavy load items , dink hoist , windlass, refrigeration, scuba compressor , could be powered , and with the addition of a hyd gen head the main engine could power 120/240v underway.

It would be far cheaper to specify hyd in a new build than convert an existing boat.

 

[sunchaser]

AF raises a good question. In industrial applications electric driven hydraulic pumps abound. Virtually all of us have an electric driven hydraulic pump on our boat, albeit a small one, on our APs. If you've ever had a hydraulic hose blow on a large yacht, and they do, the damage to joinery, carpets and then a lingering smell cannot be discounted.

When looking at a vessel with 15 plus years old hydraulic hose you are getting into replacement time considerations. A mid 2000 year Vessel is in this category with hose replacement often compromised by initial build.

Electric driven hydraulic pumps fore and aft powering thrusters is a worthy consideration on a new build, especially on builds where a genset is running 24/7. I've been on several vessels where a genset or wing engine is started to power hydraulic thrusters as powering off the idling main provides insufficient thrust.

On smaller vessel finding space for a fore and aft hydraulic reservoir is an issue. Once into the plus 60' range this design issue becomes coin flips as the cost and maintence of long hydraulic runs becomes problematic. With more vessels headed towards electric drives sans dedicated IC engines, electric motors near the energy output location like thrusters will become commonplace.

IMHO, Flyer's question is a good one and not easily discounted when looking at a sizable new build. It also raises the alternate question as to using sizable vary speed 110/240 volt motors on the thrusters with no hydraulics at all.

 

[Solly]

Wouldn't it make more sense to size the hyd. pump to work at engine idle ?? Engine would be running anyway. Pulley's or gears sized to provide enough flow or pressure to run the equipment. Electric clutch to disengage if you wanted to.
Reason's not too ??

 

[Bmarler]

Are yachts in the typical size discussed around here ever found to be using an electric motor to run a hydraulic pump for bow thruster, windlass, maybe davit/crane? With the electric motor powered by an existing ship’s generator in the 9-14kw range?

The examples I’ve seen for a trawler yacht with hydraulic systems have the pump either coupled to the main - which can sometimes bring problems with insufficient power delivered at the idle speed necessary for close quarters maneuvering - or to a separate aux. engine, which may not be practical. So if one had an existing main-driven hydraulic pump - say, belt driven - and wanted to convert the system to be driven by an electric motor instead…?

I don’t think I’d convert an existing mains driven pump, but I surely wouldn’t shy away from putting in a hydraulic power pack if it made sense. There are many makers of those systems, both ac and dc powered. Ac being most efficient. One of the best things about them is the constant delivery. Very predictable and easy to add features like soft start valves or other goodies you might want.
For high duty cycle there will be cooling issues to deal with, pump selection makes a big difference there.

 

[Alaskaflyer]

I don’t think I’d convert an existing mains driven pump, but I surely wouldn’t shy away from putting in a hydraulic power pack if it made sense. There are many makers of those systems, both ac and dc powered. Ac being most efficient. One of the best things about them is the constant delivery. Very predictable and easy to add features like soft start valves or other goodies you might want.
For high duty cycle there will be cooling issues to deal with, pump selection makes a big difference there.

Ah, so this shows how little I know about power hydraulic systems beyond the typical farm tractor. So, leave the original in place in the “loop” and add an AC-powered power pack for a belt and suspenders approach? Could something like this also function to “boost” low output from the original pump when sensed?

 

[Bmarler]

More of an either/or situation. You could add solenoid valves to switch from one source to the other. A good hydraulics guy could tell you the best way.
It would really depend on what you're trying to accomplish, ad what you might add on the future.
If your Genset is pretty good sized you can run a decent size power unit and use it for quite a few things.

 

[twistedtree]

I’ve had each of the three variants at one time or another, and as you might expect, there are trade offs with each.

In all cases I have also had a main engine driven hydraulic pump. They are great for running stabilizers, but you typically end up under powered for thrusters. It can be weak for a windlass too, especially if combined with an anchor wash. As alluded to earlier, this is because all these things are done when the engine is at idle. There are limits to how much power you can pull off an engine at idle (10% is a good starting point), and you are limited in the size of the pump that will fit which limits max flow. With twin mains it’s more plausible to size things to work. You can also kick up the engine idle speed a bit to 800-900 rpm, but no more without compromising the transmission. This all leads to an aux source of power, plus of course the desire for backup propulsion.

A clutched PTO pump off a generator can do a lot. You have the generator, so it’s a relatively straight forward add. The down side is that it can be under powered. The boat I had configured like this also had a main engine pump with elevated idle, and at times it was still underpowered. This is why it’s so common to pump such a pump on a wing engine instead. It’s also important to know that when using the generator to drive the hydraulic pump, you cannot put any electric loads on it. I stalled by generator every time when I forgot to turn off the breaker for the generator loads. The boats I know where this works have two generators with pumps that they run together.

The other question that came up is around using generator power to drive a get-home drive of some sort. The biggest issue again is the limited power available, and even more so in this case. One thing working for you is that hydraulic get home drives almost always drive the main shaft. That’s much more efficient that an off center folding prop. But even turning the main shaft, boats I know like this are typically limited to 4 kts or so in flat water.

Then come the variants on this like using electric motors to drive thrusters and get home drives, or using an electric motor to drive a hydraulic pump. All can work, but all have the same power constraints, give or take a bit.

The fundamental issue is that you generally need a much smaller generator for house power use, a good bit bigger for thrusters, and a good bit bigger again for get-home. My current boat I think illustrates this well. The relative sizes are what matter, with the absolute numbers scaling with boat size.

The generator is 25kw and serves the house loads well. That’s about a 40hp engine to drive it.

The thrusters are 35 hp each, so 70hp together. That’s about double what the generator can deliver.

Get home tops out at 160hp at about 5.5 kts. That’s more than double again what the thrusters need.

I considered a larger generator to combine the generator and wing/aux engines into one, but to get equivalent performance I would have needed a 120 kw generator plus a lot more complicated hydraulic or electric controls. Or I would have forfeited performance and/or features.

I do currently have an electrically driven hydraulic pump, principally for stabilization at rest. This was recommended over a PTO driven pump because apparently the clutches are designed to cycle rather than remain engaged for extended time, and there have been consequential lubrication and bearing failures. Electric drive on the pump solves that, but the motor is huge and so is the VFD that drives it.

 

[Lepke]

Smaller commercial fishing boats have a hydraulic pump on the main engine. Usually with a 12v clutch. A main engine is more suited to supplying the power. What I call small hydraulic pumps take about 25 hp.

Some boats use a hydraulic constant speed motor driving a generator with a pump on the main. That way main engine speed changes don't effect the generator output and they don't have to run a separate diesel generator.

Having used a lot of hydraulics, farming and fishing, I prefer it to anything electric. Hydraulics run years with little maintenance. Electric solenoids for controlling hydraulics require little in the way of amps to run. Burn outs are rare.

 

[sunchaser]

Good summary Peter. Two aspects I'm familiar with:

- On large (+ 60') twin engine vessels the ability to guide the stern with props and rudders is often better than using a stern thruster. I've seen this done while aboard 100' + vessels, never needing to use the stern thruster. I've used a warping drum to pull the stern over tight on large vessels further lessening the need for engaging the stern thruster.

- Electric/hydraulic driven thruster electric circuitry can be set up such that only one thruster is allowed to be engaged at a time, thus lowering the generator requirements. This "one at a time" hydraulic operability is common on large earth moving equipment so that pumps are not overloaded or fighting against each other.

Then comes the myriad of large single engine commercial fishing boats that have no thrusters at all.

 

[Alaskaflyer]

Wouldn't it make more sense to size the hyd. pump to work at engine idle ?? Engine would be running anyway. Pulley's or gears sized to provide enough flow or pressure to run the equipment. Electric clutch to disengage if you wanted to.
Reason's not too ??

As TwistedTree/Peter noted, you’re limited by horsepower available at the idle speeds needed for transmission shifting and slow maneuvering, for thruster and windlass use. If your main is only putting out 10HP or 15HP available for all uses at those RPMs and you have a 25 or 15 or even 10 HP thruster, well, no amount of pump rightsizing will help? It would be attractive to be able to have an electric boost pump in line with the main-driven pump which would require the least amount of changes to an existing system. If such a thing exists in a reasonable application for a medium-sized boat with a typical 8-14kw genset.

Not counting Tanglewood I’m familiar with two passagemakers owned by forum members here with dedicated wing engines - not to turn a separate feathering prop for get home, but which instead are dedicated to running a coupled hydraulic pump at the higher RPM’s needed for optimal HP output to run thrusters, windlass, maybe a dinghy crane, maybe a hydraulic AC generator, and yes, a hydraulically powered get home motor to be coupled to the main shaft in an emergency. I have come to a better understanding as to why.

For those like Lepke who have tinkered around on commercial boats with main-driven hydraulics for pot pullers, booms, line winches etc. how are they generating the HP needed, while operating at idle?

 

[FF]

"When looking at a vessel with 15 plus years old hydraulic hose you are getting into replacement time considerations."

If the boat has metal hyd lines with only a foot or two of rubber to handle vibration, its not bad.

Most sizes of rubber hose can be fitted with removable / reuseable end fittings that can be replaced as needed.

IF all have swivel ends the job is really simple , if a made up hose is carried , the repair is minuets, and low cost.


Modern aircraft use electrically actuated , hyd. operated as all that hyd fluid and pipe is heavier than wire .

 

[rslifkin]

"When looking at a vessel with 15 plus years old hydraulic hose you are getting into replacement time considerations."

If the boat has metal hyd lines with only a foot or two of rubber to handle vibration, its not bad.

Most sizes of rubber hose can be fitted with removable / reuseable end fittings that can be replaced as needed.

IF all have swivel ends the job is really simple , if a made up hose is carried , the repair is minuets, and low cost.


Modern aircraft use electrically actuated , hyd. operated as all that hyd fluid and pipe is heavier than wire .

Even with metal lines, it's dependent on the install being good. Lines routed to avoid moisture and corrosion as well as fatigue failure.

 

[Lepke]

For those like Lepke who have tinkered around on commercial boats with main-driven hydraulics for pot pullers, booms, line winches etc. how are they generating the HP needed, while operating at idle?

You start with the flow you need and match it to a pump that supplies that flow at the engine operating rpm. If you have a generator, that's probably the best because it runs at a steady rpm.

Usually small systems are belt drive with an oversize pulley and clutch. Trollers that run at low rpm only use the hydraulics for salmon gurdies, tuna pullers, or the anchor. The pump is clutched out when running at high rpm. Others use a jack shaft. A shaft paralleling the engine that with pulleys runs faster than engine speed, also usually clutch controlled. The pump runs off this shaft. Gear drive pumps are usually oversize for their application so they produce more oil at higher pressure at idle. And most commercial boat engines are larger than would be used in a same size yacht, so a large pump is a small drag on the engine.
Also there are companies that make power take offs, usually for a variety of engines. 2 jpgs are from R.C Plath in Portland, OR. But there are others. A good source for PTOs are fishing, industrial, farm supply, or hydraulic shops that cater to those industries. Most engine mfg have their own PTOs.

 

[Circumnavigator]

i

Not counting Tanglewood I’m familiar with two passagemakers owned by forum members here with dedicated wing engines - not to turn a separate feathering prop for get home, but which instead are dedicated to running a coupled hydraulic pump at the higher RPM’s needed for optimal HP output to run thrusters, windlass, maybe a dinghy crane, maybe a hydraulic AC generator, and yes, a hydraulically powered get home motor to be coupled to the main shaft in an emergency. I have come to a better understanding as to why.

That's Fintry. The bow thruster takes 60 horse, which the CAT 3406 can't come close to delivering at any speed at which you can shift from forward to reverse. The generators are a 9 and a 12kW -- nothing like 60 horse there either. So she has a separate Gardner diesel that delivers 60hp at 1200 rpm to drive the bow thruster, windlass, get home (about 4 knots) and a 3" pump which moves a ton of water a minute.


One thing to keep in mind is that hydraulics are MUCH smaller than electrics -- Fintry's 60hp get home hydraulic motor is smaller than a 3hp 240V 3 phase electric motor and weighs a tenth as much.


Jim