Hydraulic Prop Drives

[Laidback]

Can't find any specific references to having a single engine with a hydraulic pump driving a prop motor in each hull. One would think that it has great advantages for a catamaran.
My 48 ft Cat has the system with the engine mounted in a sound proof box on the duckboard aft of the Cockpit. The relatively small hydraulic motors each have a dedicated compartment in each hull. The controls allow for turning the cat 360 on its own length.

[sailvayu]

Hydraulic drives are very inefficient for this type of thing. A lot of energy is wasted in the transfer just heating the oil. Hydraulics are great for transferring energy In short bursts but long term like this not so good. I am guessing you have to have some method of cooling the oil which in turn wastes more energy. Add to that the problems with oil leaks and it is not really a practical setup. On the positive side you can tap that energy for things like windless and winches.
A better setup would be a single Electric generator with 2 electric motors to drive the props. Much less wasted energy with this and the generator can be used to power the house systems as well.
Sorry I know this is what you have but in the long run I think you will find problems with the hydraulics. I have seen it used and it never worked out real well.

Wayne Canning, AMS
Projectboatzen.com

[Laidback]

My high pressure and low flow system uses a piston type pump attached to the engine, a similar valve block for the gears, and piston type motors. There is negligible slip with this type of system, transferring more power between engine and prop, and it is much quieter in operation. I have no problem with heat as the cooling system for the diesel engine is also utilised for the hydraulics. As for hydraulic fluid leaks - not a problem with planned scheduled maintenance.
You may not be aware that hydraulically driven boats have been around for some time. I know of one that that been operating every year for some 30 years in the Norfolk Broads of East Anglia - where many are using hydraulics built by Parker Hannifin. Mine are Cessna.

Wayne, in one of the threads elsewhere in this forum the subject of Generator plus
Electric motors is covered - I am interested in member's experience with hydraulic drives in catamarans.

[sailvayu]

Interesting, I have limited experience with hydraulics in boats and all have not been good so I will be interested in what others say as well. I was not trying to turn the thread into another elec drive thread sorry if it seemed like that. I am not familiar with your type system using the piston pumps. I'll admit i am still skeptical but always will to listen.

Thanks for bringing up an interesting subject I'll sit back and listen for now, these other boats you talk about are they commercial?

Wayne Canning, AMS
projectboatzen

[FSMike]

I helped deliver a trimaran once that had a diesel powering two hydraulic shafts in the main hull. Didn"t really see the point, especially after I discovered that both shafts had to be in gear at the same time or neither of them worked. Couldn't have one in neutral.

[sandy daugherty]

I have read that there were several cats built with hydraulic drives going back to the mid 70's. There were complaints about messy leaks, and inadequate metering, but no major show stoppers. I priced out a system for a 40' catamaran a few months ago but was put off by the much higher cost compared to alternatives. I'm still intrigued by the idea, but its not in the running.

Prices were $8000 for outboards including tanks, retracting mechanisms,c controls and instruments. $26,000 for diesel saildrives with all the bells and whistles, and folding props, $36,000 for single-rail diesel AC gen, electric drive motor/generators, props, controllers, batts and bits, and $40,000+ for hydraulics.

Now if somebody put together something using off-the-shelf skid loader components, it might be done for a more reasonable cost. It would be close enough to try.

Question 1: If a drive motor is driven, would it drive another motor, so as to generate electricity? Be mindfull of the rpm needed to get something out of most engine-driven generators!!

question 2: Is there a hydraulic motor small enough to to replace the electric motor in a pod drive? [the secret agenda here is to have a steerable, retractable prop-on-a-stick!]

[smj]

We had the single diesel twin hydraulic motors in our 1972 Cherokee. It wasn'y very efficient and the cost of repairs was outragous. The diesel ran fine and was plenty of power for the boat but we couldn't get much over 5 kts out of her. We finally pulled it all out and put in a Honda 50, diffrence between night and day. If it works for you I would stick with it but when time to repower I would check into other options.

[Laidback]

"Question 1: If a drive motor is driven, would it drive another motor, so as to generate electricity? Be mindfull of the rpm needed to get something out of most engine-driven generators!!
Simple answer : yes. Also to operate anchor windlass, also bow thruster in a mono, etc

question 2: Is there a hydraulic motor small enough to to replace the electric motor in a pod drive? [the secret agenda here is to have a steerable, retractable prop-on-a-stick!]"
Depending on the design and manufacturer - My Cessna motors for example measure around 18" long by less than 8" diameter. However, there are many that are much smaller.
Here is the website of a company that has been designing, building, installing, maintaining and repairing hydraulic systems for boats since 1969 around the time "granny caught her tits in the mangle" (Cruel Sea" Nicholas Monsarrat- 1951)
WELCOME TO ARS ANGLIAN DIESELS LTD

[Chief Engineer]

I have worked on the Farymann-Hydromarin units.

Europeans have been using these systems as well as variable pitched props for years.

Like anything else mechanical in a boat....maintanance is the key.

The main advantage is you can mount the engine/pump anywhere in the vessel

What kind of unit do you have?

[Laidback]

Sandy,
Like your idea "Motor in a steerable pod" :-
--------------
Chief Engineer,
As I mentioned above, my installation Cessna - Put together by Milne Bros in Brisbane Queensland Australia. Pump connected to a Yanmar engine mounted initially in a nacelle below the cockpit floor. Later transferred the engine and pump to the duckboard aft of the cockpit and removed the nacelle.
Regarding maintenance, absolutely the most important requirement for hydraulic systems which are driving motors (as opposed to rams etc) The Hydraulic oil must be filtered - mine had a valved circuit to a high pressure filter, as over time small metal particles may be produced by the gearing components.
--------------
General comment : Way back in 1982 when first I considered a catamaran, a common response to the idea was " they are not safe! they capsize! they have no head room, they cannot go to wind, etc,etc."
I guess it may take some time for our cruising fraternity to accept that "there is more than one way to skin a cat"

[Chief Engineer]

Yeah, they said the same kinda stuff to Orville and Wilbur.

and to Kraak who invented that round stone with the hole in it.