Remote Hydraulic Transmission

[unbusted67]

I am looking into various ideas about locating an engine non-traditional locations on a boat. It seems like electric drive is going to be too expensive and now I am wondering about powering using a pump-driven hydraulic motor. I've seen this done on a couple of workboats but am wondering about it in cruising applications. My idea would be to put the engine in a hold fwd of where the shaft log is then mount the motor aft by the log/gland and connect the two with hydraulic hose. Has anyone done this?

[Bowdrie]

Yes, one time, a long time ago.
Have you ever stood next to a trash truck while they run the hydraulics to operate the forks that lift the dumpster over the cab to dump the contents?
The pros?
Fingertip control over speed and direction of rotation, and perhaps the ability to tap into the system to run a hydraulic windlass.
The cons?
Extreme noise plus engine noise.
Then there is the piping for the reservoir and cooler, the lines for the shifting and the bypass/relief valves.
A menagerie of hoses and pipes/fittings, all of them wanting to rust, and just one failure will blow enough fluid all over the place to make you want to sell the boat.
But it's the noise, it pierces the brain, it will drive you insane.

[Cheechako]

I always thought it would be a great way to go, but the reality of hydraulic systems is they create a LOT of heat and you need a way to cool the system....
and Noise.
Most systems drip somewhere. I hired a Maintenance Supervisor in a plant where I worked that had a lot of hydraulic systems to 100HP and more.
The guy I hired said "If it ain't leaking it ain't hydraulic"

[RaymondR]

Noise in hydraulic system are largely the result of the technology used to implement the system. Gear pumps and motors tend to be the worst culprits, vane pumps and motors and axial piston and motors are fairly quiet.

The simplest implementation would be using an axial piston, variable displacement, pump and axial piston motor (a vane motor could be used however they tend to have significantly lower pressure ratings)

The simplest implementation of directional control is achieved using a Morse cable to a mechanical lever on the side of the pump. A number of other control options, including electrical, pneumatic and hydraulic, are available but involve more complexity. Millisecond direction changes are possible without over-stressing any component are possible.

Leakages with modern hydraulic systems are largely a matter of quality control during implementation and servicing (and the odd leak is actually beneficial in the case of steel boats)

The biggest negative in comparison to mechanical drive systems is expense, mechanical marine gearboxes are generally the cheapest option. However in the circumstances you specify, a hydraulic drive system would be very suitable and in my opinion far superior to an electric power transmission system from a durability viewpoint.

[skipperpete]

Originally Posted by unbusted67

I am looking into various ideas about locating an engine non-traditional locations on a boat. It seems like electric drive is going to be too expensive and now I am wondering about powering using a pump-driven hydraulic motor. I've seen this done on a couple of workboats but am wondering about it in cruising applications. My idea would be to put the engine in a hold fwd of where the shaft log is then mount the motor aft by the log/gland and connect the two with hydraulic hose. Has anyone done this?

The hydraulic drive idea is a very old approach to transmitting power to the propeller shaft from a remotely mounted engine and rarely, if ever, satisfactory. I did some work on several hydraulic installations and they mostly made perfect sense such as on
1. a cruising Cat with a cockpit mounted Yanmar with two hydraulic motors, very easy to maneuver, engine in a sound shell, good access.
2. Ex America’s cup racing yacht... transverse engine, noisy oil leaking,mongrel of an installation.
3. Professionally installed system on a Tasmanian built 50’ cruising yacht yacht. This had a 12kva genset and 6-354 Perkins main engine midships.... gen on portside main to starboard....hugely expensive and seriously inefficient despite having a superb Hundested propeller on the other side of a huge complex hydraulic motor.
And here’s the thing... once you have that huge hydraulic capacity you can also run windlassess, winches, bow thrusters and even accessories like DC alternators and water pumps, it all seems to make sense until it breaks and all 3 of the above did indeed break

[FPNC]

Loss of efficiency.

The average losses in a hydraulic drive system from fly wheel to the prop will be about 18-20%. Basically you are turning an engine to turn a pump, to move oil under pressure, to turn a hydro motor, to turn a prop. With all the power losses from gearing and heat generation of same.

A properly sized mechanical gear box will have much better efficiency.

[RaymondR]

Originally Posted by FPNC

Loss of efficiency.

The average losses in a hydraulic drive system from fly wheel to the prop will be about 18-20%. Basically you are turning an engine to turn a pump, to move oil under pressure, to turn a hydro motor, to turn a prop. With all the power losses from gearing and heat generation of same.

A properly sized mechanical gear box will have much better efficiency.

Whilst the above arguments are valid the OP has an engine placement problem to be overcome. Direct drive power transmission and control systems suffer from the fact of propeller placement which then impacts engine placement.

A slight degree of of flexibility is provided by extending the drive shafts or using a V or inboard outboard or sail drive however these options can never achieve the flexibility that electric or hydraulic systems provide. Unfortunately, with the benefit of flexibility comes lower efficiencies.

My experience with modern hydraulic power transmission and control was that the axial piston, variable volume systems tended to provide the highest efficiencies and simplest arrangements.