Hydraulic drive for catamarans

Discussion in 'DIY Marinizing' started by Steve W, Nov 13, 2014.

  1. Steve W
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    Steve W Senior Member

    I couldn't find a suitable sub forum so I put the thread here.
    Ive always had an interest in hydraulic drive systems and they seem particularly useful for cats but they really don't seem to have caught on enough for a commercial system to be available and if it was it would probably be overpriced due to low volume sales.
    I admit to not knowing a lot about how they but I am aware that they may not be as efficient at transfering the power from the engine to the props but this seems t o be the only disadvantage and vastly outweighed by the advantages when considered as a package specifically for cats.
    What i would envisage would include a single liquid cooled industrial gasoline engine with a radiator and dry exhaust rather than a diesel for the following reasons.
    1/ big weight savings over a diesel.
    2/ much smoother running = less viabration transferred.
    3/ much quieter.
    4/ much less $$$.
    5/ readily available in the appropriate hp for a sailboat auxiliary application.
    6/ less expensive and more appropriate hp than doing a marinization of an automobile engine.
    There may be others i have not thought of but you get the reasoning.
    About the only advantages i can think of for a diesel are better fuel economy and less volatile fuel, having run a Yamaha 9.9 on a cat the economy was plenty good enough bearing in mind that i am talking auxiliary in a boat that can actually sail rather than a roomaran motorsailor cat.
    On the safety front, unique to the Catamaran configuration this is pretty much a non issue as the motor and tanks would be mounted on the bridgedeck with cooling air ducted in and vapors free to just drop out the bottom just like the hundreds of millions of cars on the road. So with that aside using common off the shelf industrial hydraulic pumps, motors resevoirs valves etc it should be possible to put together a system for rather reasonable cost. As far as efficiency losses over some other methods it should be possible to choose a slightly bigger hp engine to account for this. The would be a fairly light weight system comparable to outboards.
    I have seen custom systems but they usually use a diesel for whatever reason adding cost, weight, smell for no gain imho (for a catamaran)
    So, anyone know who i could get to design such a system and come up with a list of components.
    There have been a few production monohulls with hydraulic drives such as the Scampi 30 where they placed the engine under the vee berth but i don't know how well they worked and a mono cannot take full advantage of everything a gas engine has to offer.

  2. WestVanHan
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    WestVanHan Not a Senior Member

    As you likely know there have been several uses of a single engine and hydro drives on cats, Twins for one and IIRC a prout or two.

    They aren't as efficient,are loud, and don't forget the weight of the gallons of oil but for occasional use,I say give it a try. Wouldn't do it in a strictly powercat setup.

    The only real concern I'd have is your plans for a radiator,under load it's going to be very hard to get enough cooling air flowing unless you have huge rads and lots of electric fans.
    And I'm guessing with the damp air and salt spray they'll rot away fairly quickly,so go stainless.
  3. Steve W
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    Steve W Senior Member

    I was not aware of hydraulic drives in Prouts or other production cats, i have read of custom setups on a the big cat "Machette" and a Wharram or two. I had pointed out the lower efficiency but no problem upsizing the engine to compensate. Obviously not for a powercat which is why i was careful to say it would be for an actual sailing cat, not your typical motorsailor, i would think you could insulate the lines to quiet them down though. I had not thought about the noise of the oil pumping through the lines, good point. I would not be very concerned about the oil weight as the weight savings of the overall system would huge when compared to the typical twin diesel installation. Your right about the radiator, i would guess the engine would come with a plastic/aluminum version which would not last well. I don't think ducting air to the radiator through some kind of scoop/dorade box type setup under the bridgedeck would be a problem, as on a cat bridgedeck its not unlike the configuration of an automobile While you would need an electric fan i don't think it would come on often.

  4. gonzo
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    gonzo Senior Member

    I think that you haven't done the numbers for any of your claims. There are not weight savings over a diesel, you need a diesel to run the hydraulics. The hydraulic pump and motors are heavier than a mechanical transmission = more weight overall.
    There may be more vibration because of the hydraulic pump and motors.
    The engine makes the same noise level and then you add the noise of the pump and motors = more noise.
    The same HP motor cost the same regardless of what it is hooked up to. The custom fabrication of brackets, shafts, thrust bearings, plus the hydraulic pump and motors will cost more than a mechanical transmission = more expensive.
    Diesel engines are readily available whether you use a mechanical transmission, hydraulic pump, generator or whatever you want to hook up to them.
    Why would you custom marinize an automotive engine when they are already hundreds of engines available for marine use?
  5. Jim Caldwell
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    Jim Caldwell Senior Member

    I went past a Prout using one, Diesel exhaust noise and a high pitch whine!!!
  6. Richard Woods
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    Richard Woods Woods Designs

    I first worked on a central engine twin hydraulic drive system on a 40ft cruising catamaran 35 years ago. So again it isn't a new idea

    Apart from the disadvantages others mention is the fact that there is no "spare" engine. And also that most engines are actually used more for battery charging than for moving the boat. And a big engine being used for that purpose is not good.

    I have seen one set up like that where a hose burst, not a pretty sight!

    It's one of those things that people would use if it really worked, as they don't it shows there are too many cons and not enough pros. To me the biggest pro is probably the small size of the motor in each hull

    The single engined Prouts are always very noisy, but they use a single Sonic leg, not hydraulics

    Richard Woods
  7. Steve W
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    Steve W Senior Member

    Gonzo, you are right,i have not run any numbers at all but You apparently did not read my post very well, I am comparing a single GASOLINE engine running a single pump, 2 hydraulic motors, a reservoir, valving and hoses to a conventional catamaran setup with TWO DIESELS, transmissions, shafts exhaust systems, 2 sets of remotes,an extra starting battery and on and on and on. With a setup such as im envisaging weight savings would come from a lot of areas, a single gasoline engine is lighter than a single diesel of like hp and less than half the weight of two diesels, I doubt that the hydraulic components, hoses etc are any heavier than two transmissions and shafts, couplers etc, a bridgedeck mounted engine will have only one exhaust system with a very short run, vs , it goes on and on. I don't see vibration as an issue at all because.
    A/ a gasoline engine is substantially smoother than a diesel (I drive an 05 Passat tdi and a 7.3 powerstroke so I know of what I speak) and with a hydraulic drive you can use very soft mounts or even fluid mounts as you have no alignment issues to deal with.
    B/ again a GASOLINE engine is a lot quieter than a diesel let alone two, also if the single gas engine is located in a sound insulated engine box on the bridgedeck it is out of the accommodation areas altogether so a lot quieter than the typical diesels in the hulls which on many cats are inside the aft cabins. Granted, the whine from the fluid passing through the hoses could/would be an issue to deal with, it may be necessary to insulate the hoses, maybe such a thing is available off the shelf, I don't know.
    C/ The cost to buy an industrial gas engine is a lot less than a like hp diesel.
    D/ Industrial gas engines are also readily available in the hp range that would be useful for this purpose and being industrial engines there are off the shelf brackets available for mounting pumps.
    E/ I have no interest in marinizing an automotive engine for this for a number of reasons such as cost to do so, in the unique configuration of a bridgedeck location on a cat it is unnecessary, even the smallest of automotive engines are more hp than required and the industrial engines are made to run at a constant rpm driving pumps, generators etc unlike the automotive engine and, once more, they are readily available for a lot less money than a diesel industrial let alone a marine diesel. Again, a gas engine mounted on the bridgedeck is as safe as the engine in your car, unlike a gas engine in the hull of a monohull for example.
    Look, im not a hydraulic engineer or even play one on tv but i do know this has been done before but in every example i have read about they have used a diesel, i love diesels but i think for this application only, a gas engine is more appropriate for the reasons stated above. Again, just to be clear, i am talking about an AUXILLIARY application in a proper performance sailing catamaran, a boat that will be sailing, even in light air, where an auxiliary is used for getting in and out of the marina and motoring when there is not enough breeze to sail at, say, 5 knots. I am not talking about the more typical floating condos that you see motoring all over the place when there is a good sailing breeze and i am not talking about powercats.
    My reason for starting this thread is with the hope that someone may know of someone who has used a hydraulic drive on a cat, with success or not so much or if someone can lead me to a hydraulic engineer who could put together a list of appropriate off the shelf parts required, for a fee of course.

  8. Steve W
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    Steve W Senior Member

    Hi Richard, I know its not a new idea, as I said I have read articles over the last 30-40yrs or so but i cant help but think that the biggest reason it has not found favor is more that there has not been a proven off the shelf propulsion package available. I know that there is a lack of redundancy but i could live with that, after all, even though I can get out and get a cab home i cant think of a time in the last 30 years where my car engine has let me down and stranded me. Also, i have relied on a single outboard as an auxilliary on my last 2 cats, it is after all, an auxiliary to my main source of propulsion, the sails. Hundreds of thousands of monohulls get by with a single auxiliary. One of the problems with cats is mans need for symmetry, the feeling that you need 2 rudders, 2 daggerboards, 2 engines. When you get away from the diesel you have one fuel source, for the main engine, the dinghies outboard and for battery charging, again a nice Honda 2000e could be permenantly installed in a vented locker or in the same compartment as the main engine with a remote well muffled exhaust to the underside of the bridgedeck and plumbed into the main fuel tanks. I would put a single fuel source in the pro column.
    Yes, hoses can burst, but in general hydraulics are very reliable and are used to propel vehicles from small earthmoving equipment up to the huge trucks they use to carry hundreds of tons of iron ore at a time on the iron range here in Minnesota. When i put together a list of pros and cons there are a lot more in the pro column. I would love to crawl around on a boat with a successful system installed and get the part numbers off all the components as they will all be off the shelf industrial items, readily available, for reasonable money, not marine. That's in the pro column for me.

  9. WestVanHan
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    WestVanHan Not a Senior Member

    About 12 years ago I got the cat "bug" and had thoughts of sailing around the world-Caribbean,Australia etc. But then remembered that I really hate hot humid weather and that there was cheap 747 flights every day,so that idea was dropped.
    At any rate I did see several Prouts with hydro drive for sale.

    All you really need to do is look online for an industrial supply-mining,lumber mill,manufacturing supply company.
    Everything will be there including calculators for pumping losses/pressure drops,pump size for torque requirements,hose size requirements,etc

  10. Steve W
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    Steve W Senior Member

    I have been doing a little research on industrial engines, as i expected an industrial gas engine is lighter than a comparable diesel but i was surprised at by how much. Its a little hard to find true comparables but I was able to compare an LRG-425 Ford carbureted engine 2500cc max 74hp intermittent @ 3600rpm at 339lbs dressed, A Toyota 4Y gas carbureted 2237cc 59hp @ 2570rpm @ 227lbs ( I don't know if that's intermittent but I assume so) to a Kubota V2403-cr-e4b 2434cc, 50.2 hp intermittent @ 2700rpm with a dry weight of 487lbs. This puts the Toyota at less than half the weight at 260lbs lighter and the Ford which is the biggest hp of the 3 at 148lb lighter.
    As I mentioned it is a little difficult to do direct comparisons as they don't all give all the specs but they are all dressed industrial engines and all weights given are dry. The Ford gives the most complete specs including intermittent and continuous torque and hp @ 1800rpm which is nice. The point is the weight differences between gas and diesels is huge which is why i am so interested in them specifically for bridgedeck mounting on a cat where the common safety issues are a non issue along with of course the other advantages of smoother running and much quieter and ,at least here in the US the cheaper fuel offsets the better economy of a diesel. I was looking for the dry weight of an industrial 4-108 Perkins but no luck so if anyone has this it would be appr
  11. Barry
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    Barry Senior Member

    A fellow I knew ran a company in Alaska that installed and serviced hydraulically driven work and fish boats. A couple of comments that he made to me were that with a single pump and single motor, with valving you will see a 25% power loss. Adding in another motor and more valves, perhaps you should add in another 10%.
    So if you want a combined effective horsepower at the shafts of say 70 hp, you will need about 100 hp input into the pump.
    The other thing that he mentioned that they usually calculate about half to a gallon of reservoir capacity per horsepower to deal with the cooling of the hydraulic fluid. A good piece of the horsepower loss manifests itself as heat. To reduce the size of the reservoir, you should consider a water cooled intercooler to deal with the heat.

    Your comment about using an automotive engine as compared to a marinized one relates more to safety than anything else. In any boat, to meet ABYC guidelines, the air inlet needs to be flame arrested, the distributor, starter, and alternator the same. While you could hide it, it is unlikely that an insurer would insure a boat with an engine that was not marinized.
  12. Steve W
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    Steve W Senior Member

    Thanks Barry, I was told by the guy at air/hydraulics that running 2 pumps for 2 motors will use less oil for cooling but this is going to be the biggest factor as to if it is a viable system or not. A 48ft Catana i sailed on once was powered by a pair of 27hp Volvos with saildrives . I don't know what the mechanical losses are with saildrives but they were adequate. Lets say 20hp per side at the shafts so im thinking something around 60hp and lets be clear, gasoline.
    By installing the engine on the bridge deck vented to the bottom on a catamaran is a unique situation and is as safe as the engine in your car. I don't know how insurers would treat it but its common sense. If a gasoline engine is installed down in the hull of any boat, especially a monohull that heels over, yes it absolutely needs all those safety features in place, no question. I have actually witnessed with my own eyes a powerboat explode at the gas dock at a local marina and a guy come out the fwd hatch with his back on fire so I have a healthy respect for the danger of gasoline fumes in the bilge, But this is different, all the vapors will just fall out the bottom just like on a car, likewise the fuel tanks would be on the bridge deck vented to the bottom, it is no less safe than an outboard. Some of these industrial engines are available fuel injected. I don't know if its any safer as far as flame arresting. Starter and alternator are no big deal to replace if need be. As far as not marinizing i mean i would use the automotive style cooling system with a copper/brass radiator, electric fan etc. Again, made possible by bridge deck mounting.

  13. keysdisease
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    keysdisease Senior Member

    Some of the French cats put the generator on the bridge deck forward of the mast, Lagoon 500 below, the white space center forward.

    For a variety of reasons, some mentioned, this is problematic from an airborne noise / vibration perspective. And while gas engines are quieter and operate at higher frequencies than diesel engines, it's still an engine.

    As for the plumbing, the longer the oil run the more loss of efficiency from plumbing friction. There are also challenges with exhaust and raw water, a radiator is not typical for marine installations and will really make things loud. Isolation mounting a comparatively light hydraulic motor with a high thrust to weight ratio is very challenging. To do it right you need to treat the hydraulic motor like a thrust taking gear / transmission, think remote v drive, all possible but not cheap to do right.

    I am aware of a current catamaran project with the centerline generator replaced with a motor generator and the drive diesel engines replaced with electric drives. Even though the space previously held a diesel generator, there were some real challenges.


    "To operate all the boat's appliances when under way or at anchor, a generator, too, is essential. It's housed in a large machinery space in the bridgedeck forward of the mast, accessed through the sunning cockpit, along with the propane storage locker and other auxiliary equipment. "

    A few thoughts. :cool:

    Attached Files:

  14. black_sails
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    black_sails Junior Member

    Thread necromancy!

    I like to follow up for others who may be reading the same topics of potential interest in the future, i'm curious if OP ever pursued his plan further.

    As I shared in another old thread I just responded to, the efficiency loss of hydraulics is about at best 80% and perhaps at worst closer to 65%, those are numbers I learned trying to research building a hydraulic hybrid car for better mileage that made me quit the plan entirely. That's a pretty serious kick in the groin for fuel efficiency. The loss of driving the pumps are pretty constant as well, in a similar fashion (but far worse) to simply disabling the power steering pump on many vehicles will gain you 1mpg, because the parasitic losses are pretty substantial. Combine the loss of fuel efficiency going gasoline over diesel and youre could be looking at half the MPG and needing to carry and pay for twice the fuel. For short cruising the greater weight of fuel wouldn't offset the diesels, at some larger size it would. If that's not a detriment then sure.

    Lifespan might be the next issue, many smaller gas engines spinning at 3600rpm to make that higher power need a rebuild after about 700-1000 hours of use. For something used a few hours on a few weekends per year not a big issue but the more you use it it starts to matter.

    But since you specifically said this is just for use as an auxillary? In the very small size ranges you might find two small gas outboards to be even simpler, redundant, more efficient, and at the end of the day not costing much more (near as I can tell you will spend thousands rigging up the hydraulic for this, which is what a 2nd gas outboard costs) or being much noisier. (does noise in the marina matter if it's honestly spending most of time at sail? Plus having them on the tail of the cats 20 feet away from you with shrouds and sound barriers so that sound goes back away... i'd think that even quieter than a super quiet mounting box up on the deckhouse near where you are.) I think the reason it's not a common solution to have a ready made package is most people for the same weight and cash would prefer the simplicity and reliability of two GAS engines to one gas engine.

    The better question might just be answering "gas vs diesel" with gas instead of engineering up a custom hydraulic system with more points of failure chasing what might in the end be elusive benefits. It might be easier to try and mount a single outboard in the middle between the hulls or on some custom drop mount coming down from your deckhouse if you were dead set on one gas engine only. And save the hydraulic engineering for raising and lowering it from the water more than the usual amount motors tip up if it's lacking the normal protection motors have being mounted off the back of a hull.

    PS - oh, and a saildrive shouldn't have any loss as far as i'm aware over any normal outboard/inboard mounting point. So 27hp saildrive is just 27hp. Comparable hydraulic motors should then also be around 27hp and assuming losses your gas engine size jumps up to more like 68-85hp sustained (as 27hp yanmars can run 100% all day long) and i'm not aware of 25-30hp hydraulic motors and 85hp pumps being the cheapest things offhand either. I'm just pretty sure it will cost thousands to engineer up. :-/

  15. Steve W
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    Steve W Senior Member

    Quite a surprise to see this thread back from the dead in my inbox. I currently have a cat with a single center mounted outboard that works quite well. Hydraulic components can be found inexpensively in many surplus places but you need to know what you are looking for. Every so often you come across a cat with a hydraulic drive system that works well despite what others may say, it would be great to get onboard and just get the model numbers off the components. The reason I like gasoline rather than diesel for a centrally mounted engine are many such as lighter weight, cheaper to buy, much smoother, quieter etc but to be clear, I am talking about 4 cylinder industrial liquid cooled engines such as those used in forklifts, these engines are very long lasting, toyota forklift engines have been known to exceed 50000 hrs before a rebuild. Also to be clear, a gasoline engine is as safe as it is in a car only if it is properly mounted in a vented space on the bridgedeck of a catamaran, not down in a hull of any boat. On the bridgedeck it is out of the accommodation and any fumes can drain out the bottom. With a hydraulic or electric drive the engine can be very softly mounted to reduce vibration even more.
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