Hydraulic Drive Ideas

[NCboatrx]

Hydraulic drive is doable but expensive and inefficient. If done properly you will get about 25% losses to the propeller. I suggest that you research the Technodrive / Twin Disc or the PRM mechanical transmissions. These will fit in place of your Hurth and generally give great service.
Stanley

[forsailbyowner]

What is a fluid drive transmission besides a pump and drive motor in one package. The boat in question has an 18hp diesel. So the pump and drive motor are not on the scale of cummins v8 or the like. Have to do some torque conversions and research to find correct torque output from motor and pump. I got the idea from a german friend of mine that mated a volkswagon automotive diesel to a pump and used it to drive 2 motors on a home built catamaran. One huge plus is having the engine remotely mounted in an insulated cushioned box that could concievabley be easily removed for service. Running a gen head off same motor would also be attractive and eliminate the desire for a separate genset engine. Gotta research those loss numbers. Both pump and motor, some can be used for either claim 95% efficiency. Where did the other 20% go?

[boatpoker]

Check out Fisher catamarans one diesel, twin hydraulic drives.
Prout cats also made some like this.
Also know of one Mainship Pilot single engine with twin hydraulic drives and A Halman 20 converted to look like a tug (Fisher Price style) with a hydraulic drive.

[Florida Mike]

Where did the other 20% go? Mostly HEAT & associated cooling equipment, I believe. Mike

[NCboatrx]

Originally Posted by forsailbyowner

What is a fluid drive transmission besides a pump and drive motor in one package. The boat in question has an 18hp diesel. So the pump and drive motor are not on the scale of cummins v8 or the like. Have to do some torque conversions and research to find correct torque output from motor and pump. I got the idea from a german friend of mine that mated a volkswagon automotive diesel to a pump and used it to drive 2 motors on a home built catamaran. One huge plus is having the engine remotely mounted in an insulated cushioned box that could concievabley be easily removed for service. Running a gen head off same motor would also be attractive and eliminate the desire for a separate genset engine. Gotta research those loss numbers. Both pump and motor, some can be used for either claim 95% efficiency. Where did the other 20% go?

How much power do you want / need at the prop? You claim 18HP for your engine so how much of this can you afford to lose? Here is two links to hydraulic propulsion systems which will explain some of it 1) Beta Marine | Marine Diesel Propulsion Engines and Generating Sets 2) Hydraulic Propulsion

I am certain that someone trying to sell you a system will claim better efficiency but experience with boats and long runs for hydraulic systems suggests otherwise.

[DeepFrz]

This is from Beta Marine's hydraulic web page.

• The engine and hydraulic pump unit can be sited anywhere in the boat and this maximizes the use of space.

• The engine can be sited away from the steering position to give a quieter running ship.

• Very flexible speed control is available at low rpm.


• Transmission power losses can be between 20 to 30% or more, depending upon the hydraulic pipe run lengths; so the system is on average about 20% less efficient than a conventional engine and gearbox combination where the losses are approximately 7%.

• Generally a hydraulic solution will cost more than a standard mechanical drive.

[forsailbyowner]

Ok my hose run for the hydraulic drove will be about 2'. Was picturing running the engine transversley right behind the prop shaft where there's a shelf already that used to hold batteries. If cooling is an issue can simply run a cooler inline like velvet drive does. Were not talking huge hp here and I think some are comparing apples to oranges. Most tractors lawnmowers etc are hydrostatic drive these days. Thinking of a kubota tractor my parents purchased recently with a similiar engine. All hydrostatic drive with hydraulic bucket etc... Research continues as the engine is very close but newer.

[David M]

Keep in mind there is a loss of efficiency through conversion to waste heat when converting from mechanical to hydraulic and back to mechanical power. Is it worth the loss of efficiency with Diesel costing so much? The same goes for electro-mechanical systems.

Is it also worth the additional complexity? The more complex something is made the more likely it is to break.

More energy efficient and less likely to break sounds like a pretty good thing to me. That is a beauty of a propeller shaft. There is only one conversion of energy, engine heat to mechanical energy. There is no having to then convert it to fluid energy and back to mechanical energy, with its energy losses and additional complexities. Again, the same goes for electro-mechanical systems and their two additional energy conversions.

[onestepcsy37]

still, i think if i had the time and the $$$ i would try this not too expensive experiment -

old 16 foot runabout from craigslist - $300
old hydrostatic tractor from craigslist - $250 (just bought one)
bits and pieces (maybe the lower unit from an outboard motor) - $200

voila! a $750 hydraulically propelled boat!

[Irish rambler]

There's nothing new in hydraulic drives for boats, UK/European hire boats have the system fitted for over 25 years and they work perfectly well. The French company Jeannau are now producing hybrid hire boats with joystick control, many of the first hybrids needed a mechanic following, later models seem to be slightly better, but what they'll be like after 20 years is anyone's guess, I wouldn't touch one with a barge pole. I would ditch the Hurth box and fit a recon Borg Warner, end of problem, Keep it simple.

[forsailbyowner]

I'm keeping in mind while doing this that this is being built as a bluewater cruiser. I finished a sail yesterday 1000 mi. 30 mol days. No motor. And this wasv in the Morgan OI that everyone says sails like crap. The diesel wil see far more use spinning a generator head which won't be much either. I have one boat that is a somewhat motor sailor (the oi) that will be the coastal cruiser. The Offshore I'm building as an offshore boat and the mechanical drive imho on this boat is inconsequential.

[sww914]

Factor in the price of some props, too. A good prop shop can tell you what you need if you tell them what you have but that won't apply here.

[forsailbyowner]

Weighing the ins and outs for the desired result this is looking more and more attractive to me. Even with the losses having 12.6hp available for the drive motor , a windlass, a winch drum at the stern, or a generator head eliminates more complicated systems than it creates and adheres to the kiss principal. Hard plumbing the long runs will save a bunch on hydraulic lines. Using teleflex cable so the hydraulic valves are placed inline would save on a lot of plumbing.

[forsailbyowner]

As for plumbing and prop cost, nearby is a marine salvage yard I've been doing business with for decades. They have a wall with hundreds of props hanging. I'm quite sure I can keep trying different pitches and sizes till I find something that works. He'll also give me credit for trading in the current one. There's a whole building full of used and NOS fittings valves pipes and hoses also. I have a mast a couple booms and other stuff to barter with him so not a bunch of money needs to change hands there. First step. Fire diesel up on stand that hasn't run in I don't know how many years.

[forsailbyowner]

Looking at this pump,

https://m.northerntool.com/northernt...ductName=false


And this motor.

https://m.northerntool.com/northernt...do?itemId=1001

The kubota puts out about 2/3 the torque the motor is rated at and the pump and motors numbers seem to jive. Will definately need more research though