effeciency loss question about hydraulics/generators

greetings.

this is nearly follow-up to an earlier thread, but different enough to warrant a new post, i believe.

presuming the need for a generator on your boat, it seems like it might be worth the efficiency loss to instead have an engine tied to a hydraulic pump. you could then mate a hydraulic motor to a generator head for your dc generating needs, and ALSO have the convenience of hydraulic power for any of countless other needs.

so my question is, how substantial a loss in efficiency are we looking at to power a generator head via hydraulic motor instead of a dedicated traditional generator? do you think the advantage in cost in buying only a generator head VS traditional generator would off-set the cost of additional hydraulic motors?

etc etc

 

So lets continue here.
With closed circuit hydraulic transmission (pump/motor) you can achieve some 80-85% effiency.
The total gain/losses compared to either conventional (main engine/mechanical transmission + generator) or diesel electric depends how well the system are optimized to the task.

 

i'm sure the chance of getting exact measures of efficiency would be very difficult with such a hypothetical question...

are you saying around ~80% efficiency as far as getting mechanical energy from the engine to the generator head? that sounds pretty good, considering i saw on another thread where ~90% efficiency for a Sterling generator was very good.

particularly considering you can get a 12kw generator head for under $400 compared to at least three times that for a traditional generator (according to 5 minutes of research on ebay), and you'd be able to use the hydraulics for other applications to boot.

also seems to be the advantage of being able to pu your generator in a non-ventilated compartment would really help extend the life of parts?

 

Remember on a boat you just cant throw in any genset. It needs to be marinized like any engine.
On the other hand closed circuit hydraulics are't excactly cheap either. I made some cost estimates for a 50kw total power system and just the hydraulic pumps and motors were allmost 10k€ ($13k) and that didn't include any control units, valves, tubing, accus etc. Only reasonable way to get the hardware cheaper is to chop them from older Bobcat etc.. and if it's old it's with older and less efficient parts...

 

@teddy : could you explain a little more about what you mean by 50kw? that seems like a whole hell of a lot of energy, but i'm only thinking in terms of electricity... and i suspect your measure is a combined?

can anything be "marinized" or is that specific to how it's constructed from the get-go? a quick search on ebay reveals a cheap gas/hydraulic pump combo (http://cgi.ebay.com/11HP-PETROL-ENG...hash=item310110004099&_trksid=p3286.m63.l1177) that puts out more than enough flow and pressure to run a huge variety of motors... including ones that will give over 1000fps of torque (http://cgi.ebay.com/NEW-Eaton-Char-...5|66:2|65:12|39:1|240:1318|301:0|293:1|294:50), which should be enough for even a main drive. similarly ebay has 12kv generator-heads that are under $400 (http://cgi.ebay.com/NEW-12-KW-ST-GE...5|66:2|65:12|39:1|240:1318|301:1|293:1|294:50) and could be run by a hydraulic motor.

of course, neither of these boasts any kind of "marine readiness". the generator-head, if powered by a hydraulic motor, would require no ventilation. could that be "marinized" simply by sticking it in a sealed compartment?

 

jason yoiu really should apologise to Rick w , for the comment you made to him
He is our resident expert, and can teach us all much

 

@woosh. this isn't the thread i believe you are referring to, that is here (http://www.boatdesign.net/forums/boat-design/distributed-hydraulic-systems-boats-why-not-25792.html) link for anyone interested.

i don't really see a need to apologize. the least kind thing i said was that i felt he was being silly to imply that i was suggesting that *every* system on a ship be run via hydraulics. specifically his remarking that he 'had not yet seen a hydraulic powered gps'. when anyone makes such an obviously jabbing comment they should expect to get called on it, and that's all that i did. particularly when one of the advantages i listed of using a hydraulic system was that you could power a generator-head to supply all of your electric needs. so he clearly hadn't read my whole post, or was choosing to ignore parts of it.

beyond that, i only refuted his opinion that a hydraulic system should be more prone to the effects of corrosion than an electrical system. i believe he mentioned the fittings being particularly vulnerable. i don't think that either of us were at all venomous in our replies to each other. but i appreciate the concern for trying to keep this wonderful website a friendly place

 

A diesel 71hp connected directly to variable pump giving at diesel engines max rpm fluid volume/pressure equal to 50kw (well.. a bit rounded up fig) feeding hydraulic motors for propeller, generator, compressor, winches, thrusters.
Too complex and expensive.. anyway for me, but got to figured it out so.
Now it looks I'm choosing variable pitch propeller and do the other stuff electric..

 

torque isn't everything as you know...
Though I didn't check it looked more like open circuit hydraulics, and though they work reliably and are adequate for some purposes, with open circuit the effiency is far worse and not a proper solution for completely hydraulic solutions. If you intend to run a relatively small generator and some other things short periods at a time it's an easy, cheap, maybe a bit noisy answer...