Hydraulic Propulsion?

[Chief Engineer]

I have a customer that has a hydraulic system powered by a 1 cylinder Faryman Diesel. It is an Irish Built boat. It does have a good bit of push at manuevering speed, but not much top end.

You will need a large reservoir for hydraulic fluid and for extended running a oil cooler.

If cruising you will need a spool of spare hydraulic hose as well as fittings and the proper tool/experience making hoses up. And lots of 5 gallon pails of fluid in case something thats a shinola in the night.

[delmarrey]

Originally Posted by cagney

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.

Part of my last job was stopping leaks in heavy equipment (P C'er for a City government). Believe me leaks can be stopped. I plumbed up my own hyd. steering system and it doesn't loose a drop, yet!

Now part of my job is testing large valves of all kinds and pressures and even a 24" check valve can be sealed 100%.

There are bio grade hyd. oils available. A couple I have used, one is a vegetable oil used in grounds maintenance equipment and the other is water soluble, blue in color, used in car washes and equipment in eco-sensitive areas.

[stevensc]

Done right it will not leak, it is a very convenient way to transmit power but is much less efficient than conventional systems and will generate lots of heat. Not the way to go.

Steve

[jrd22]

I had a 29' Cascade that had a hydraulic drive. It worked really well and we never had any problems with leaks. It's rare to have a leak with the modern hose and fittings available as long as you don't have any chafe issues on the hose. The engine can be mounted anywhere, and there is no alignment issue other than the hydraulic motor to the shaft which is easy. Docking was a breeze, just set the throttle for the engine and then use the forward/reverse lever to control the prop speed. With the engine at full RPM in forward doing over hull speed you could throw the lever into reverse and stop on a dime. The only issue we had with it was noise, it made a high pitched whine at cruise speed that was annoying, I am sure that it could be lessened with some heavy duty noise suppression. I always wondered about the thrust issue from the shaft, but it never caused any problem while we had it (several years). We never had a problem with the hydraulic oil getting too hot, had a fairly large reservoir, but in a hot climate you would need a cooler. Hydraulic machinery is very reliable, lot's of heavy equipment is all hydraulic (excavators, travel lifts, etc.). There is a loss of about 15% efficiency, that's probably why you don't see it used much, and the additional cost, but it does add a lot of flexibility.