Hydraulic Propulsion

I'm convinced that it's possible to use hydraulic fluid pumped from a normal marine engine to turn a prop. If the connection between the engine and the prop is simply hoses, then one could place the engine anywhere on the boat. There would also be less problems with alignment, universal joints, vibration, maintenance, etc.

Does anyone know of a firm that builds this type of drive system?

 

How bout a stern paddle wheel. Seen them built here in the 60 to 300 foot range with hydraulic power. Pretty noisy, I would think a prop would be inefficient.

 

Hydraulic propulsion is certainly feasible, the problem is efficiency. The hydraulic pump efficiency is typically 90% to 94% and the hydraulic motor efficiency is typically 98% to 99%. This equates to an overall efficiency of 88% to 93% compared to conventional gearbox efficiency of 98% to 99% or a net loss of about 10%.

Effectively you will need a 10% larger engine to achieve the same speed and >10% more fuel to achieve the same range.

You will also need an hydraulic fluid cooler to remove the additional heat because all the lost power ends up as waste heat in the hydraulic fluid.

One of the main advantage of a hydraulic transmission is it allows multiple engines to drive a single propeller.

Let me know if your still interested and I'll provide some links when I get home tonight.

Regards;
Mike Schooley

 

Stuff...

Hello...

I have installed and worked with Engineers (over the phone ) on a few of this companies systems in the past...

See http://www.quantumhydraulic.com/...

How about a couple of modified bow thrusters - Korted. - http://www.marinepropulsion.net/hrp/hrp.htm ..

Yikes...

SH.

 

Hydraulic drive units are in production and used quite a bit over seas, yet to catch on in the states. The engine can be run at the best RPM for the conditions, like an idling engine in a smooth sea with the prop spinning fast or in heavy going, slowing down the prop and spinning up the engine. You get the best economy for this arrangement. Tied to a variable pitch prop the unit can be rather efficient to use.

The engine can be mounted where the weight can do the most good or be out of the way. Heat can be used as well, both the engine and fluid lines can have heat extracted for other uses, like hot water or cabin warmth. According to most hydraulic drive manufactures, the current units are near as efficient as a good marine transmission.

 

Hydrostatic transmissions approach the efficiency of gear transmissions however they achieve this efficiency by closely coupling the hydraulic pump and motor and optimizing the fluid passages between them. This defeats the benefit of being able to separate the engine and drive shaft.

To allow the propeller rate to vary relative to the engine with high efficiency, then a variable displacement pump must be used (it is possible to decouple the engine and propeller speeds with a bypass valve, but this just wastes the excess energy so in general it is undesirable for long term operation). Variable displacement pumps are considerable more complex and more expensive that continuous flow pumps.

If you using a fixed pitch propeller and it is optimized to operate near the engines maximum continuous output point, then there is no benefit at the design speed, a conventional transmission can provide the optimum gear ratio more efficiently than a hydraulic drive. The benefit of the hydraulic drive is at lower boat speed, where the propeller power demand curve is lower than the engines optimum power output curve. In this case the hydraulic drive allows the engine to operate at its optimum speed independent of the required propeller speed. This not only improves engine efficiency, which may compensate for the hydraulic drive efficiency, but it also extends engine life by eliminating operation in an under-loaded condition and by reducing engine revolutions (some people believe engine life is more closely to revolutions than hours of operation). If you have a system that will operate for significant periods at much different power outputs, like a commercial tug, then this may be a good alternative.

It should be noted that during the low power operation mode the propeller will be operating far from its design point so propeller efficiency will suffer. A better solution might be to use a controllable pitch propeller, which would allow the pitch of the propeller to be optimized for the desired boat speed and allow the engine to operate at its optimum speed. The controllable pitch propeller provides the same benefits to the engine as the hydraulic drive, but it also provides higher propeller efficiency, so overall efficiency is higher.

Regards;
Mike Schooley

 

I have seen a richard woods catamaran with hydraulic drives . It has a single engine mounted to port of the hull centerline in the port hull ,close to midships . Driving two hydraulic drives situated aft of midships inboard of the hulls .

 

I'm very interested. Any info would be great.

 

Just because you can doesn't mean you should. It's a terrible idea for all but a very few cases, mostly involving gearing ratios that are difficult to achieve with off-the-shelf options. Some limp-home systems that use hydraulic pto units are an example. Tugs are another. The cost and huge increase in footprint needed to accommodate and provide access to the hydraulic piping is a big concern. Shafts take up no space at all compared to what the hydraulic pipes will need. The picture below shows a 400 hp hydraulic attachment on an excavator. Do you want that blue thing on a 400hp boat? Are you thinking where you will put the 200-300 gallons of hydraulic fluid?

 

These used to be widespread and very well regarded in oyster farming barges in NZ. Hydraulic drives can be easily lowered and raised, because there are flexible hoses in place of a shaft. This is ideal for use in the intertidal waters that oysters are often farmed in. They've generally been replaced by four stroke outboards.

 

Perfect example of a factor outside cost and efficiency being the more important input. I've talked to some west coast oyster guys over the years, they utilize some of the same shallow draft techniques as my fishery. We both value the performance in shallow over raw performance or efficiency. Even so about half end up going traditional prop/shaft or outboard and coping with degraded shallow water performance.

20 year old thread. Not a great idea then... still nota great idea now.

 

There isn't much of penalty from going outboard for shallow water, especially with jack plates. The main risk would be silt accumulating in the cooling system, but that can be resolved by running in clean water.

 

In my narrow bandwidth it's cracking/breaking lower units and knocking off prop flukes. But the last decade or two of four-stroke obs and better production jack plates has helped.

 

On the Norfolk Broads there are hundreds of boats using diesels to drive hydraulic motors.The boats are displacement types and the hulls tend to be 25 ft to a prescribed limit of 46 ft overall and they are mostly used for weekend or longer breaks by people with little or no boating experience.The limitations of the region nudge the designs in the direction of shallow draft and a low superstructure that will pass under old bridges.By using hydraulics,it is possible to locate the engine somewhere other than on the centreline of the hull and thus the accommodation layout can be freed from the constraints that a central engine would impose.Given the heavy usage pattern of the boats,40 hours in a week is not unknown and more can be logged if the engine is run while moored for battery charging.From time to time a user will allow a boat to sit on the mud when the tide drops and blocks the cooling intake.Which makes a change of engine necessary.It helps the business hugely if the engine change can be carried out swiftly and it is a handy attribute when the winter maintenance has to be done as it is always easier to access the peripherals with an engine on a stand instead of in a cramped compartment.

The boat in the picture has an engine located at the stern and transversely mounted.Which means that once the hatches are lifted,there isn't much work to do in order to remove the engine and once the replacement is installed,there is no need to carry out any alignment.Combine this with not having to dismantle chinks of the interior and the advantages are clear to see.

 

Those are tiny systems. Maybe you need a 3' wrench to loosen the hydraulic fittings on a 10 hp hydraulic circuit. On a bigger system, say a 2" line fitting, you normally drop a bulldozer blade on the tracks of an excavator, then hang a 5' pipe wrench on the fixed side, slide an 8' pipe over that, then chain it back to the bulldozer with binders. Then you can put another 5' wrench on the hose fitting, slide another 8' pipe over that, and get 2-3 guys to jump on it for a few minutes. If that doesn't work, go get a backhoe and bang on the pipe with the bucket. I've seen a 15,000 pound backhoe hanging from the pipe and the fitting not give up. That's about 150,000 ft pounds torque. How are you going to do that on a boat? These are circuits that deliver maybe 200 hp. Quick connects aren't much better. Besides the price, I sometimes have to pull them off with my dually. It's amazing how much a few grains of sand can jam up a connector. Hydraulic maintenance isn't for the timid.

The thing about a 2" or 2.5" prop shaft is you don't need 10' of room to swing a wrench in order to do basic mintenance.