hydraulic drive

[mbogo]

How many designers specify or offer a hydraulic drive option? Why isn't this a more popular option for engine installations? I'd think that the ability to mount the engine anywhere (and put it truly horizontal on its beds) plus not having to worry about prop shaft-engine alignment, etc would be a couple of very strong points in its favor. There is an extra complication of running hoses, but that doesn't outweigh the benefits, at least in my thinking. Are there repair/reliability issues in a marine setting? The industrial, construction, and farming hydraulic systems I've worked with have been pretty robust and reliable.

[Ross M]

"Why isn't this a more popular option for engine installations?"

My four part guess:

a) efficiency
b) complexity
c) cost
d) weight

Ross

[chucksw]

Hydraulics are used extensively in marine applications for steering, winches, windlasses, aux. power equipment on large boats and ships. But typically not for the main prop drives. The cost, size, and wasted HP in such a setup would be huge.

[Jay Greer]

I agree and am considering the installation of a hydraulic drive unit in the next boat I plan to build.
We humans are creatures of habit and most often are happy with things as they are. By all means, like Alexander the Great, cut the Gordian Knot of hydraulic drives and go for it!

[Jay Greer]

I forgot to mention that there will be a loss of power.

[Chub]

This is very interesting. I would like to see actually how much power loss would result from a hydraulic drive.
Engine placement might make up for inefficiencies cause by the hydraulics.
;)

[P.I. Stazzer-Newt]

There was some discussion on this topic HERE. (http://www.woodenboat-ubb.com/ubb/ultimatebb.php?ubb=get_topic;f=6;t=004627)

[Ross M]

"I would like to see actually how much power loss would result from a hydraulic drive."

I think it is safe to assume that readily available pumps and motors have an overall efficiency of somewhere around 85%.

.85(pump)x.85(motor)=.7225 system (ignoring losses in controls and piping)

So you are looking at the low 70's, compared to the low 90's of a typical transmission/shafting arrangement.

So now you need 20% more hp for equivalent performance, And the vicious cycle begins to get really ugly.

Bigger engine means heavier engine and larger fuel burn

Which means even more engine, more fuel, and heavier support structures.

Which means even more engine, and yet again more fuel (albeit in smaller and smaller increments).

Pretty soon that transmission and shaft are looking pretty good.

And then a 3,000 PSI line breaks and spreads the oily everywhere.

And don't forget: Hydraulic oils are typically flammable or ferociously corrosive.

[WWheeler]

Also a shorter lifespan for the install than a direct drive.

[Keith Wilson]

Well, there might be other benefits. One wouldn't need a transmission; reversing and speed control would be done with valving and possibly a variable-displacement pump. It would seem to have some real advantages for auxiliary power on a moderately large sailboat, since the hydraulic motor is fairly small, and you could then put the engine in a more convenient place.

[mbogo]

I'm not thinking for a big boat, or even a power boat. The small scale of things used for say a 25 to 35 foot sailboat do not require large engines in the first place. Some loss of horsepower is to be expected, but how much power do we really need? So you buy a 15 hp diesel instead of a 12hp one (just as an example). Fuel requirement differences would be negligible, unless you planned on motoring for substantial distances. I think the ability to tuck the engine where the size and weight fits the best is a big advantage - rather than trying to design the whole interior of the boat around where that engine sits on its slanted beds.

A valve box has to be less weight than a transmission, which would make up for the fluid in the lines. Hose inspection should be done regularly for any system anyway: deck hydraulics, head lines, fuel lines, etc. Hydraulic drive does have some drawbacks, but no worse than a traditional direct drive and a transmission, if you ask me. Anyone have an idea on how the two drive systems compare in cost? I would bet that a hydraulic system could be set up to the same or less money than a standard drive system.

[P.I. Stazzer-Newt]

I found this web page. (http://www.engineeringtalk.com/news/par/par193.html)
An explanation of the what, how and why. It looks like a neat, tough idea.

[htom]

Ocean Navigator had an article a couple of years ago: http://www.oceannavigator.com/article.php?a=1303

[Leon Steyns]

As above and with a picture. I really like this idea.
http://www.vetus.nl/indexns.asp?lang=2&productid=115

http://www.vetus.nl/images/producten/product943_foto1.gif

[Edited to remove the link to the Ocean Navigator Online article].

Greets, Leon Steyns.

[ 08-18-2005, 06:43 PM: Message edited by: Leon Steyns ]

[Nicholas Carey]

Originally posted by Keith Wilson:
Well, there might be other benefits. One wouldn't need a transmission; reversing and speed control would be done with valving and possibly a variable-displacement pump.That also means the engine that ultimately provides hydraulic pressure can run at a constant speed and optimum power efficiency, since the hydraulic motor can be controlled with valving. The resulting increase engine efficiency should make up for some of the power lost due to hydraulic inefficiency.

[Gerald]

I considered a hydraulic drive for the boat that I am building but didn't run across a good source for a unit large enough. I found great big units and small ones. A good start for small output units might be garden tractors with hystat units. Anyone that has owned a garden tractor with a hystat would probably laugh at you if you started talking about power loss! You might ask Case or a manufacturer how much loss there is instead of relying on guesses from folks that have never owned one.
I own a car with a hydraulic transmission. I am one of the few on the island with an automatic transmission. The locals claim that automatics slip, waste gas, and are just sissy items. Put me in the sissy category. However, I am always first away from the stop light, first to the top of the hill and fastest when I pull into the passing lane.
I have never owned a boat with a hydraulic drive but I would like to. The sailboat I am building has the motor set over the keel, level, low and runs back to the prop thru a truck drive shaft. If I were building a power boat it would for sure have a hydraulic drive.
Sissy Gerald

[JimConlin]

The lost power goes to heat and noise which might not be welcome.

I've heard of a couple of catamarans with one engine and two drives. The concept was thought to work well.

[mbogo]

The oceannavigator.com article was an excellent read - thanks for that link. I hadn't considered all the applications for hydraulic drive on a boat. I was thinking mostly just driving the prop. The more I think about this, the better hydraulics appear. I wouldn't go as far as plumbing the whole boat with hydraulics, personally. If I could use one engine to drive the prop and an anchor windlass, that would be plenty good for my needs. I still like windvane steering and person-powered sail handling! I just don't like having to mount the engine under the companionway steps at an angle to line up with the prop shaft.