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.

[Gianfranco]

Interesting information. I am not looking at efficiency and will put up with some noise since it will not be run a lot. Only in and out of places.
Can someone help me with sizing?
I plan to get a 15 HP gas motor, (prefer diesel but, the weight and cost are too much).
Will add a 2000 Psi hydraulic motor with the capability of 10 GPM and a matching motor.
This should give me a bit over 10 HP at the shaft.
Only two hoses will be inside with most connections outside.
I prefer solid SS tubing but, I am limited to working with 3/8” tubing and I believe that is too small.
Reason.... MONEY, convenient installation, and weight. A 9.9 HP outboard is about $5000 with a remote control.
The engine ??? anyone will do and sure will rust to death but, they are cheap and easy to replace.
Any suggestions?
Thank you, Gianfranco

[Bowdrie]

Originally Posted by Gianfranco

Can someone help me with sizing?
I plan to get a 15 HP gas motor, (prefer diesel but, the weight and cost are too much).
Will add a 2000 Psi hydraulic motor with the capability of 10 GPM and a matching motor.
This should give me a bit over 10 HP at the shaft.
Only two hoses will be inside with most connections outside.
I prefer solid SS tubing but, I am limited to working with 3/8” tubing and I believe that is too small.
Any suggestions?
Thank you, Gianfranco

Your boat is a C&C 38?
They originally came with an Atomic 4, and there was barely enough room for it, (IIRC they made both ~18Hp and ~30Hp versions).
If you plan a 15Hp engine for a 10Hp hydraulic you're already way down on power.
I'm certainly no expert on hydraulic drives, but at 2,000psi can you even transmit 10Hp with 3/8ths lines?
You still need a cooler a reserve tank and a filter, plus the controls/valving.
All that takes up a lot of space, (in a boat with very little "spare" space).
In a salt-air environment, If the connections are steel, they will start rusting as you look at them.
On a lightweight boat such as yours I fear that in going to hydraulic drive you will be jumping from the frying pan into the fire.
If a high pressure line/fitting lets go, you'll wish you were in Kansas and had never seen a boat.
Perhaps an expert on this will chime-in and show that I'm wrong.

Addendum; calculated Hp from 2,000psi at 10gpm is 11.67Hp.
But can 3/8ths line carry that?

[skipperpete]

Gianfranco, you’re right about ⅜ tubing being too small, spinning a propeller shaft at 1,000 rpm takes a fair bit of oil flow and a ⅜ tube, while ok for a windlass, is too small for your propshaft. Your plan is do-able but it might be a stretch at $5,000 and its a steep learning curve and some tricky calculations to match the pump to the motor. Corrosion can easily be prevented by liberal use of “Denso tape” , a grease impregnated bandage wrapping known and loved by trawler engineers and plumbers for protecting pipework and deck hydraulics…. It really works. I doubt that cooling the oil will be needed but if it is a problem, a simple oil cooler in the hopefully low pressure return line should be adequate, deep sea trawlers just use keel cooling pipes to cool their high power hydraulic systems. I guarantee you’ll use your propulsion system far more often than you plan so build it with that in mind.

[Gianfranco]

It is for an F32 trimaran that I am almost finished building....

[skipperpete]

Originally Posted by Gianfranco

It is for an F32 trimaran that I am almost finished building....

Ahhh , that makes sense, weight and space are the issue , plus… its a sailing machine.

[Bowdrie]

Originally Posted by Gianfranco

It is for an F32 trimaran that I am almost finished building....

Jeepers, I'm glad we didn't get 3 pages into this before learning that the boat you're talking about isn't the one in your avatar.

Originally Posted by skipperpete

Ahhh , that makes sense, weight and space are the issue , plus… its a sailing machine.

Yes, weight/space?
A 15Hp engine and its tank/plumbing/controls/panel, plus hydraulic pump, plus hydraulic motor, plus all the related stuff for the hydraulic system will all take little space and little weight, right?
An F32 is a folding trimaran that you can tow with a car.
Build a well in the center hull, stick in an outboard and be happy.

[boatpoker]

Originally Posted by Bowdrie

Your boat is a C&C 38?
They originally came with an Atomic 4, and there was barely enough room for it, (IIRC they made both ~18Hp and ~30Hp versions).

I've only surveyed 8 of these and spent a lot of time in the C&C plant and never saw an atomic four in a 38'. All I've seen had Yanmar 3HM35F's and engine access was about average for a boat of that size. What model years did you see them with A4's ?

[Bowdrie]

Originally Posted by boatpoker

I've only surveyed 8 of these and spent a lot of time in the C&C plant and never saw an atomic four in a 38'. All I've seen had Yanmar 3HM35F's and engine access was about average for a boat of that size. What model years did you see them with A4's ?

I used Wiki, according to them there was a 38-1, 38-2, 38-3.
The -1 and -2 models had A4s, the -3 had a Yanmar.