boat power ( hybred ) efficiency Hyds.- electrial (AC or DC )

[bjsmarine]

Gentlemen -- Me again with my dumb questions --- But again I have been asked a question that has me baffled.
As I once explained I am a mechanic not an engineer so please be gentle.

My latest query -- If one were to rig a modest power plant in a vessel {under 300 HP.} and wanted to go the route of power take off to shaft . power plant to generator to electrical motor (AC / DC } or Hydraulic Pump - motor .

The Question is efficiency ,
From what I have been able to make sense of is that in a perfect world 85 for hydraulic and 92 AC electrical.

Fact is that the world is not perfect - Marine environments being right up there on the list .

So I guess what I am hoping for is some direction regarding power versus propulsion in the real world ,

Hybrid propulsion has been around longer than I have -- But there must have been great advances in the business recently and along with that I'm sure failures also. So am most interested in any feed back - pros and cons - efficiency ratings - anything and everything


Thank you as always
Bob

 

[MikeHalloran]

Steyr is now selling, or trying to sell, a small high speed Diesel coupled through a compact motor/generator, as a marine hybrid package; just add batteries.

There are so many energy conversions involved in a hybrid that I wouldn't expect particularly good efficiency, and there are so many sales people involved in hybrid markets that I wouldn't believe any numbers that are quoted.

There are a few markets where a hybrid of some kind makes a lot of sense; garbage trucks for one. Lobsterboats should benefit in pretty much the same way. In both cases, operation at low speed and operation at high speed are interleaved. The hybrid system stores power by running the engine at high power until the batteries or accumulators are charged, and not at all while they're being discharged.

Steady high speeds or steady low speeds don't benefit from a hybrid.

Bottom line: In constant power operation, hybrids are no more efficient than, and probably much less efficient than, simpler drivetrains. They can potentially save on fuel costs in cyclic duty, like driving in a city, or operating a water taxi. Whether the fuel savings will pay for the additional hardware and weight requires some fairly complicated calculations to predict.

One factor that works against hybrids in marine service is that, unlike garbage trucks, they can't recover much energy in deceleration. Potential absence of noise and smoke in crowded anchorages might be a usable selling point. Same argument should apply to hybrid yacht generators; you can control the acoustic noise from a Diesel, less so the smoke, smell, and slobber.




Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Aside from the information given above by MikeHolloran the link below gives a real good cross section of what out there for all shapes and sizes.

As eluded to above why are you required to use a hybrid drive?

http://www.yachtboutique.com/BentleyMarine/Technology.htm

 

[bjsmarine]

thank you gentlemen for your replys. most heplful info. and all will be taken in carefull consideration.
Unclesyd. As to why , The boat that is being considered to be built the main purpose is to get to a given station in a timely fashion and then stay on station with out aid of a complex system of anchors.
The obvious solution would be a series of trusters positioned - frd. aft, port , stbd, and perhaps adjacent to all quadrants .
If this were all to happen it would be obviously through a power system of either electric or hydraulic motors driving thrusters monitered and triggered through gps and a complex computer system or a good skipper . All of which is non of my affair. But if so such a array of power take off`s ----why not the main propulsion ?
This comes back to basic quiery.
Energy loss. Hydraulic pump to motor or generator to electric motor . AC or DC.

Thanks all again
Bob

 

[MikeHalloran]

It's entirely possible for a boat to be propelled by a Diesel-electric system, not unlike what locomotives use. It's more common in larger boats, where you might find actual locomotive engines for propulsion, and in some ships. Note that's not a 'hybrid' system; its a 'Diesel-electric' system.




Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Here is a little more information, abbreviated, on all aspect of marine propulsion.

http://www.masson-marine.com/en/mar...-speed-device-or-trolling-valve_05_06_00.html

You should be able to locate a lot of information on new boats especially the drill-ships and work-boats in the Gulf of Mexico. Nearly all the new one have station keeping ability.

 

[JRMacGregor]

Transmission efficiency is far higher in electric power systems than in hydraulic systems. There is NO question about that. Hydraulic is also more noisy.

However, small marine applications (like the 300 hp you talk of), often make use of hydraulics because the electric drive equipment is not so available in smaller sizes.

The dynamic positioning you talk of for your vessel is a well established technology for larger ships - like offshore drilling vessels.

For them (7500 hp on each thruster including the main propulsion) they use AC alternators and variable speed AC drives.

Your thrusters need to vary the output. You can do this two ways;
- variable speed propeller, fixed pitch
- fixed speed propeller, variable pitch (pitch adjustment also requires hydraulics)

For your application, I suspect the decision will be dictated by the availability of controllable motors for the thrusters in the size range you need. If you can find small variable speed hydraulic driven thrusters, then that will be big driver for your decision.

By the way - I think this is the wrong sub forum for this type of question.