Hydraulic Propulsion?

[GDFL]

Does anyone here have any experience with hydraulic drives for boats? I am in the process of designing a boat and I've been thinking about propulsion and power generation systems. The boat will be a long, effiecient power cat. I was trying to think of ways to not have 3 diesel engines on board, but still have propulsion from each hull. I have no idea of the cost and reliability so that's why I'm asking for the input.
What about having a small diesel of maybe 20hp and a larger diesel of maybe 70hp. I was looking at the drive unit mentioned here: Hydraulic pumps save Hong Kong yachts from damage: News from Parker Hannifin I'm thinking the smaller engine could run the hydraulic units in both hulls while at slow cruise and the larger diesel could be used in conjunction with the other as the need arises. Power generation could also be taken off of the hydraulic system from whatever engine is running. I'm guessing that the hydraulics would cost more than a traditional two engine plus generator setup. Thoughts?

[DeepFrz]

There was a thread on here a short time ago and one person had loads of trouble with his hydraulic drive system. He had a link to his website, but I can't remember what the thread was about. A lot of the trouble was in the design of the system, which was professionally done. He was very dissatisfied with it.

[Evan]

It can be done but it's noisy, hydraulics ALWAYS leak eventually, and you will have at least 20% power losses due to the conversion. Oh yes, it will be expensive too. Why do you need the generator?

[delmarrey]

First, Hyd. motors/pumps will not last as long as any reciprocating motor. You would need a cooling system for long runs or one heck of a large reservoir and hope you never blow a line.

Second, you'll be losing some of your milage per gal. ratio. Transferring power from one mechanical source another just wastes a percentage of the fuel.

All you'll be doing is adding to the complications of you vessel, plus the extra weight.

You should consider diesel electric way before hydraulics. As for Hong Kong, short runs maybe fine but they just need to learn how to master their boats. Nothing is idiot proof.

[Pblais]

Does anyone here have any experience with hydraulic drives for boats?

My first boss out of college had a 60 ft paddle wheel boat in St Paul, MN on the Mississippi. It was powered by twin stern paddles driven by hydraulic torque hubs. The torque hubs were powered by two diesel engines that were used to run the refrigeration in over the road trucks. The boat burned 1.5 gallons per hour and could carry a full USCG approved load of 90 persons but normally would carry 40 persons comfortably on two decks. The draft was 2.5 ft and had 4 rudders that were about 4 to 6 ft long. The wheel itself was a farm tractor wheel hub with steel spokes and frame for each paddle board. Each wheel could be powered in opposite directions for tight turning. Should the boat strike a log and break a paddle you could bolt on new board(s) just like the old river boats did. In flat water it did about 7 knots. It was pretty quiet and really a great party barge. The mechanical system held up quite well for the 6 years I worked for the company. The vacu flush heads were probably the one part of the boat that took the most work. The hull was all steel and they froze it in place in the winter.

The large diameter of the wheels with the low rpms of the hubs made the solution work quite well. I don't know how fast you could turn a screw with hydraulics. The boat also had keel coolers for the fluid. That would be a concern for any hydraulic propulsion system. This was a totally home brewed system.

[delmarrey]

Originally Posted by Pblais

My first boss out of college had a 60 ft paddle wheel boat in St Paul, MN on the Mississippi. It was powered by twin stern paddles driven by hydraulic torque hubs. The torque hubs were powered by two diesel engines that were used to run the refrigeration in over the road trucks. The boat burned 1.5 gallons per hour and could carry a full USCG approved load of 90 persons but normally would carry 40 persons comfortably on two decks.

Now that system would work well. Torque motors are a vane motor that turns fairly slow and with hardened parts, AND very expensive (around $800+ ea.) for the ones Paul mentions. But to turn a screw, high RPM𐑈 would wear down a hyd. motor fast.

[Lancerbye]

I remember seeing a hydraulic propulsion system on a commercial Salmon troller. It had been a fairly expensive instalation but worked well for their application. Trying to slow a salmon troller to a near stop but still have forward drive has always been a problem. They had achieved this with this system but had not saved anything on fuel consumption or got any better speed. But those were not their primary concerns. For a regular drive system I don't see the advantage. As Delmarrey and others have stated wear on hydraulic motors would be a factor. Rebuilds on hydraulic equipment is not cheap. A leak in this big of a system would be a huge ecological problem.

[Pblais]

The RPM's on the torque hub above were maybe 70 to 80 max. underway. Any more and you wee throwing water. You started and controlled the engine throttle in the engine room and had a kill switch and controlled the torque hubs from the wheel house. Low rpms with a lot of power still sounds like it might still work OK. I think the keel coolers may have been 8 to 10 feet long with one per drive but it was over 30 years ago. It was a fun boat to pilot with a monster twin set of horns.

[GDFL]

That's about what I figured. I didn't know if there might have been some practical installations or not. A generator isn't absolutely necessary, but solar panels aren't always going to give you enough power and I hate running a main engine just to charge batteries.

[Talbot]

Hydraulic propulsion. Strictly speaking every propulsion system is hydraulic because it uses the force of water to move the vessel.

I assume you are talking about hydraulic trannsmission. There are advantages and disadvantages of this:

Disadvantage

more losses in efficiency than a conventional system.


Advantages

Ability to have significant power at very low revolutions

Ability to position the engine where you want, - this is taken to extreme in some catamaran designs where they use a single engine to drive two propellors through hydraulics.

Ability to power other hydraulic systems such as bow thruster or windlass.

[sushirama]

try the boatdesign.net forums there a lot of info there.

[Cheechako]

I've often wondered why Hydraulic motors aren't used more. The advantage is you could put the powerplant anywhere you want and just have hoses going to the hydraulic motors at the shaft connection. Also, no transmission. There is likely a reason though. A hydraulic guy I know once told me "if it aint leaking... it aint hydraulic"

[delmarrey]

Originally Posted by Cheechako

A hydraulic guy I know once told me "if it aint leaking... it aint hydraulic"

He obviously reused old fittings.

[cagney]

Originally Posted by delmarrey

He obviously reused old fittings.

Well... not necessarily. Metal to metal seal hydraulic fittings, for example standard BSPP or JIC fittings, are more prone to leaks than a solution that include a soft seal as well , for example the ORFS or german DIN fittings.

An interesting possibility, that I would love someone else , to test on a cruiser is Water Hydraulics. To use water instead of oil as a hydraulic fluid. Check this Intro to Water Hydraulics for example.
Most likely way to expensive, but food for thought.

[Lancerbye]

Cagney
Interesting article. I installed a Hynautics dual station clutch and trottle system on a commercial boat some years back. Used a 50/50 distilled water and antifreeze mix as a fluid. This was a pressurized hydraulic control system. Worked slick as heck. No cables. However that was not a motor.