Hydraulic drive for Catamaran?

[Cadence]

Originally Posted by rjdives

The system works great for motoring too, we have made 200nm crossings under power with no problems.


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I have been attempting to get a figure on energy lost. Best I can find is about 30%. That may not be much worse than running twins? For the redundancy of twins, I'd have a get home outboard or just a sail..

I'm glad you had some input that isn't pure BS from those that don't know anything about hydraulics.

[Sailor Doug]

30% is pretty good for hydraulic system likely close to 50% all depends on design and component selection. Electric dives have replaced hydraulics for most industrial applications.


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[Cadence]

Originally Posted by Sailor Doug

30% is pretty good for hydraulic system likely close to 50% all depends on design and component selection. Electric dives have replaced hydraulics for most industrial applications.


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I doubt that. Elevators use to be powered by Ward- Lenard systems. I'm told today they are hydraulic.?

I'm old school. The OP only asked about have hydraulic drives had been tried, by this time I guess he has an answer.

[Sailor Doug]

Originally Posted by Cadence

I doubt that. Elevators use to be powered by Ward- Lenard systems. I'm told today they are hydraulic.?



I'm old school. The OP only asked about have hydraulic drives had been tried, by this time I guess he has an answer.

Sorry I build big machinery for a long time. Hydraulics are now avoided. Elevators may be converting to it. That had to avoid compressed due to freezing water in compressed air. Most elevators used a lot to long cables. They may now be using some hydraulics with eatable oil.


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[Cadence]

Originally Posted by Sailor Doug

Sorry I build big machinery for a long time. Hydraulics are now avoided. Elevators may be converting to it. That had to avoid compressed due to freezing water in compressed air. Most elevators used a lot to long cables. They may now be using some hydraulics with eatable oil.


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I do not disagree with the cables. As I said I am old school. Ward-Lenard is an ac motor driving a DC gen and motor as I recall for controllability and torque, may still be that way over several stories? Compressed air has me confused along with eatable oil?

[Sailor Doug]

Originally Posted by Cadence

I do not disagree with the cables. As I said I am old school. Ward-Lenard is an ac motor driving a DC gen and motor as I recall for controllability and torque, may still be that way over several stories? Compressed air has me confused along with eatable oil?

I may have confused your reference to elevators to the agricultural storage and processing of grains.
So is this why I had a drip of oil down my neck the last time I stayed at a Holiday Inn?


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[rjdives]

Originally Posted by smj

So the weight of the hydraulic system would pretty much equal a new Yanmar 3gm30 with saildrive. Our hydraulic system on our Cherokee was made by Volvo and was extremely expensive, but I'm sure there are better and less expensive alternatives.


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Around 400lbs is my guess. But then your fuel tank for the second engine which is another 3-500lbs depending on the size of the tank. Room for another water tank or more batteries


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[a64pilot]

Hydraulics would come into their own if you had bow thrusters, powered furling gear, winches, windlass,etc. The more "stuff" you need to drive, the more viable hydraulics become.
You give up some in efficiency, and gain in flexibility, imagine a cable driven backhoe


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[smj]

Originally Posted by rjdives

Around 400lbs is my guess. But then your fuel tank for the second engine which is another 3-500lbs depending on the size of the tank. Room for another water tank or more batteries


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You are absolutely correct. The single diesel twin drive hydraulic system we had worked fine but was getting old and many parts needed replacing. We pulled the whole system and went back with a Honda 50 mounted in a nacelle we built under the bridgedeck.


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[Sailor Doug]

Originally Posted by a64pilot

Hydraulics would come into their own if you had bow thrusters, powered furling gear, winches, windlass,etc. The more "stuff" you need to drive, the more viable hydraulics become.
You give up some in efficiency, and gain in flexibility, imagine a cable driven backhoe


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That's a lot of potential leaking fittings.


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[a64pilot]

Look at all the heavy construction equipment that has thousands of hours with little or no leaks, and commercial boats with hydraulic cranes and winches.
Just twin engine sail drives can be bought off the shelf, whereas a hydraulic drive would likely have to be designed.
It's like a hybrid Diesel Electric, I think it's viable, but they are certainly not mainstream, can't buy an off the shelf solution, therefore very unlikely a boat manufacturer will try to design their own, and if they did, it may not work so well.

No reason you couldn't do either hydraulic or hybrid electric, for one thing either would free up engine mounting location, now the drive line has to be the primary driver in engine location, but either electric or hydraulic and engine can be mounted anywhere.

I don't want either, I like KISS, but that doesn't make either non viable


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[smj]

Originally Posted by a64pilot

Look at all the heavy construction equipment that has thousands of hours with little or no leaks, and commercial boats with hydraulic cranes and winches.
Just twin engine sail drives can be bought off the shelf, whereas a hydraulic drive would likely have to be designed.
It's like a hybrid Diesel Electric, I think it's viable, but they are certainly not mainstream, can't buy an off the shelf solution, therefore very unlikely a boat manufacturer will try to design their own, and if they did, it may not work so well.

No reason you couldn't do either hydraulic or hybrid electric, for one thing either would free up engine mounting location, now the drive line has to be the primary driver in engine location, but either electric or hydraulic and engine can be mounted anywhere.

I don't want either, I like KISS, but that doesn't make either non viable


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All the heavy hydraulic construction equipment I've seen have 5 gallon jugs of hydraulic fluid littering every square inch. In fact, I know where the trash man has been by following the trail of leaking hydraulic fluid😕


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[captlloyd]

Well, it has been an interesting thread with answers all over the board. I am thinking of building a cat and thought I might get your opinions. Two points I need to disagree with. #1 You can't get drives off of the shelf. I disagree with that, pumps and motors are available pretty much all over including the internet. #2 Leaks. The plumbing and fittings would need to be maintained just like any other drive system. (think saildrives for example). I have seen garbage trucks going down the road that look like they have not had any maintenance for years !!
At any rate, thanks for all of the thoughtful replies. (I probably will go with the traditional twin diesel/straight drives. Ha, I am such a chicken!)

[RaymondR]

The thread is getting very interesting as more people who have actually experienced hydraulic drives contribute.


There is a world of difference between the hydraulics systems which can be implemented using modern hydraulics as against those only a few decades ago.


Modern closed loop systems can be built to remain sealed for the life time of the system which may actually outlive two or three engines and the life span of fully welded and flanged piping systems is limited only by the corrosion potential of the metals they are fabricated from. If you want to go to the expense of all stainless this is probably hundreds of years of leak free service.


The long life of a closed loop system properly sealed is due to the perfect operating environment, every moving part is bathed in a liquid with excellent lubricating properties and the system is sealed against an contamination.


The variable displacement, axial piston pumps and motors referred to in my previous post offer the opportunity to adjust engine loading to optimum for either engine life or fuel economy. In the case of fuel economy one emulates a piston engine aircraft where the propeller pitch and throttle settings are adjusted for maximum fuel economy.


In the hydraulic drive case the engine throttle is set to a high idle and the pump displacement varied until an optimum system power point for best economy is established. Using both drives to manoeuvre and come up to speed then shutting off one prop is possible if this delivers optimum fuel economy.


The efficiency of the pumps and motors mentioned can be about 96% and this does not vary much between manufacturers, of which there is a veritable host.


Most mono's have a single engine and their owners are happy with this situation and consequently would probably be satisfied with a single engine and two props independently driven. For my part I would not want two of the noisy smelly beggars and the problems that come with them, however I am a simple old dude and most multi hullers appear to revel in the complications hull-ism brings.


Modern electric drive systems have similar characteristics to modern hydraulic systems with similar advantages and disadvantages however the thought of sharing the same space as an electrical drive system in a small vessel in a salt water environment horrifies me and as an old oil driller I am accustomed to being around traction drive systems managing hundreds of volts and thousands of amps.


I tend to the opinion that as boat designers become more familiar with the types of modern hydraulics systems available and the advantages they provide we will see more of them on pleasure vessels.

[NSboatman]

Well reasoned post rr. Good to hear from one with experience and the ability to share it.

I've seen several get-home systems in motor yacht using hydraulics. A very sensible application where a pto-driven, bent axis variable piston pump of th type your refer to is mounted on the front of a suitable generator or auxiliary. These systems work very well, if designed properly and maintained; and provide buckets of lovely, continuously rated output for things like anchor windlasses, bow thrusters, cranes and davits, etc.

Like all systems, it's a triumvirate of design-installation-maintenance.

The key difference (from electrical systems for example) I've found in the various hyd systems I've dealt with is: cleanliness IS godliness. Nothing causes more issues in hydraulics than contaminated fluid. It's not that hard to keep things clean, but it starts before a single piece of gear shows up on the boat, and continues with every fitting, pipe, hose and liter of fluid. Nothing is usable directly from the 'store' (not even buckets of oil). Purging, flushing, filtering and inspection are mandatory for every single component in contact with the fluid. Meticulous adherence to manufacturer specs and environmental isolation will result in an extremely reliable system in the end.

I think in the small vessel world, the balance is probably tilted toward electrical distribution as friction losses become significant on small lines; and weight of components is proportionately higher (you can only go so thin on cases and mountings). But for mid to larger vessels it stareTs to make a lot of sense.

I noted with interest that a canal barge I rented in France in 2012 (LeBoat) used a transverse mounted nanni with a drive system as I outlined above. Was very quiet, reliable, and efficient - on flat water mostly below 6 knts. Very nice install. I think the main advantage in that install was that the entire engine bay looked and felt like the underhood of a typical car- very compact, modular, contained behind a firewall. Also the extremely short shaft (might even have been an extension of the motor shaft) meant lighter bearings and a simplified stuffing box.

Ymmv!



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