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Diesel Electric Propulsion

Discussion in 'Technical Discussion' started by Crewagency, Nov 26, 2004.

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  1. karo1776

    karo1776 Senior Member

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    No fooling... The problem with electric machines is much like thermal machines like steam plants and diesel engines... they have been designed for a certain loading or most efficient point of operation. But electric machines fool you because they are pretty much just lumps of iron and copper or magnetic material and turn on an off with the flip of a switch... so that is somewhat misleading.

    What is interesting to me is that in this forum often I hear about generator sets running at their best efficiency at full load... as far as fuel consumption per unit output. This is herein always explained as the engine part is most efficient at that point. No that is not the case. The generator is most efficient at that point as it was designed for that point. The diesel likely is not.

    But the diesel is actually most efficient near its torque peak which is usually at lower rpm than rated. In fact, diesels are typically best at part load at part rpm of full rated. Now this is heavily dependent on the particular diesel.
    But as a typical a diesel rated at 1800-2000 rpm... might be most efficient at 1400 rpm and about 2/3rds rack. Now an example... and maybe Nilo can help here... it seems to me Moonen typically tailors the cruise speed of their displacement yachts at a point of most efficient per unit output on the diesel main engines. The problem I have in explaining this is that engine manufacturers often have several ratings for the same engine.
  2. PacBlue

    PacBlue Senior Member

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    I hear the term efficiency attached to a diesel engine alot, but maybe your question can be best answered by defining what do you mean by efficiency - is it specific fuel consumption, torque, power vs. displacement, TBO?

    What are you describing when applying the term efficient to a diesel engine?
  3. karo1776

    karo1776 Senior Member

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    Specific fuel consumption... hp per unit of fuel
  4. PacBlue

    PacBlue Senior Member

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    Then your earlier comment "But the diesel is actually most efficient near its torque peak which is usually at lower rpm than rated. In fact, diesels are typically best at part load at part rpm of full rated. " would not really apply to modern diesels today?

    Look at the fuel maps on today's diesel engines (Generator or Propulsion) and you will see that the lowest (best) specific fuel consumption values are typically at full rated power.
  5. Opcn

    Opcn Senior Member

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    The reason that ships are propelled more efficiently (nm per unit fuel) is the ship, not the engine. There is a diminishing point of return on those extra horses in the water.
  6. K1W1

    K1W1 Senior Member

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    Hi,

    That is because this is what the market desires, n one is going to sell an engine that can do 2000 Kw and say its best fuel burn is at 800 are they.

    With the amount of fuel required to turn the calorific value of it into a moment of force about a point and a unit measurement in thousands there needs to be sufficient oxygen for complete combustion, sufficient heat in the whole thing to get the fuel to burn when injected.

    At full wellie and full load you will find that all these variables are near or at their peaks where today's engines work their best.
  7. karo1776

    karo1776 Senior Member

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    Truth spoken... you know your stuff.

    A basic diesel engine not tied to a particular application or engine rating, will be most efficient at much lower output (yes, K1W1 800KW is about the most efficient point for 2000KW capable engine). Now the 800KW might be reasonable for continuous output (like a generator) but the 2000KW that engine can put out might be reasonable for fast patrol boat for like a 5 minute rating for a few hours a year. But the opacity of exhaust will be greatly different at each of those outputs.

    So if that engine is used for a generator application it will be derated from its Maximum intermittent rating for to a Maximum continuous rating in that application. That 50 Hz 4 pole generator set running at 1500 rpm... and max load at that point is always much better in fuel specific than the same basic engine running at 2300 rpm in high intermittent application....

    A large engine like K1W1 points out might be rated at 1800-1900 rpm for the 2000 KW intermittent but be run at 1000 rpm in a 50 Hz 6 pole generator setting.

    But the generator manufacturer is not going to tell you that basic engine could produce 2000 KW for your generator set... as you'd actually expect it to do that all the time!!!

    Why I mention opacity is that black smoke coming out of the engine at 2000KW likely would not met any environmental concerns and choke to death whoever is berthed next to you... not to mention the roar might keep up nights... and you might find some kind official visiting with fines in mind.

    This is confusing more so because usually the injectors, turbos, maybe even cams (rarely), maybe even compression ratios etc will all be tailored to the specific application now-a-days. Common rail electronically controlled injections systems don't even have a "rack" anymore... so that is an old fashioned saying.
  8. K1W1

    K1W1 Senior Member

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    When I ask for a genset proposal with a maximum output quoted I expect this to e what it is capable of 24/7. Gensets are not normally offered with A,B,C,D,E Ratings like propulsion engines.

    A propulsion engine and a Genset Engine are actually quite a different animal.

    They have differences in design of fuel system, intake and exhaust ( camshaft, turbo nozzle) and fuel control system.

    CAT's no longer have a static fuel timing figure on their data plates, something that has caused more than one MCA Examiner to question the sanity of an applicant after asking what angle the start of injection is when told there isn't one.

    They might not have the physical equipment but the term is still valid even if it is shown as a percentage.
  9. PacBlue

    PacBlue Senior Member

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    Sorry, I am not buying the 800/2000kW ratio analogy, especially on a Specific Fuel Consumption basis (grams per kW - hour). Under load for a propulsion application, you will typically see your best specific fuel consumption to the right of peak torque, nearing rated power, if not at it.

    For a generator Application, best Specific Fuel Consumption will come at 100%and it increases (drops efficiency) as load reduces (75%/50%/25% or whatever) and this should hold true for Constant or Variable Load profiles.

    Most applications fail to adequately identify their true power needs (Propulsion or Generator) and over install on kW, and then commence to operate their engine equipment at lower than expected Load/Operation Profiles, and they will never see the optimum efficiency (grams per kW - hour) that can be achieved by a modern diesel.

    To the best of my knowledge, all modern diesels (Propulsion or Generator) for sale today are tied to a particular application and engine rating. So if you need 800 kW Continuous, then get that particular model/application/rating, don't spec a 2000kW Intermittent or whatever to only run it at 800 in a Continuous application (for example).

    Do the engineering upfront.........
  10. karo1776

    karo1776 Senior Member

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    Then aren't you all very glad I am not working or designing on diesel engines... and left the engineering dept. over 30 years ago!
    Sadly realizing too late I should have never gone down into that grubby sweaty hole in the first place.

    As my grandfather said, long long ago... "don't go into engineering"... "those guys run around in their skivvies... always sweat pumping over something... always *****ing an moaning... breaking down when you least need it"... "you want to command the boat not run it."

    His best advice... "If you don't make someone else do it you will have to."

    This brings to mind diesel electric submarines have been operating a long long time. Usually with one diesel generator and batteries... so maybe that's the best set up. Maybe not as efficient as a dozen little generator sets but sure simpler. I'll read all the contrary posts tomorrow if I get up!
  11. Yachtjocky

    Yachtjocky Senior Member

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    Grubby holes

    Your grandfather should also have told you that you would never get anywhere if it was not for those guys in skivvies going down into those grubby sweaty holes.

    As for his other "sound advise", in 44 years as an engineer I have never made someone do something because I did not want to do it, in fact I have "never asked" someone to do something I have not done myself. :cool:
  12. karo1776

    karo1776 Senior Member

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    Diesel Electric... Concept Development Possibilities

    That's noble... but every naval officer or merchant mate... has to learn that if you are to command... your orders must be followed... and starting out running the deck crew... do you really want to paint the ship yourself... etc or make those who's job it is to do it... you are the manager and quality guy meaning you are absolutely responsible for the work and product... it is your job!
    That nobility may be in the enlisted or signed on crew doing the work but its not so much in the officer corps!

    Back to diesel electric... and complication... in my hypothetical concept development boat of 40m displacement boat example. Right now sizing and capacity is educated estimates only.

    What I am wondering from the forum members experience what would be the most practical "basic configuration". So right now the sizing is estimated guesses... that maybe others will have some comment on.

    This is general setups not for a particular boat right now but as an exercise in concept development.

    The choices are:

    1. 6 generator sets (all identical) staged to come on line with load demand and share hours. Sizing would be 175-200 KW. There would be two oil bath shafts for propulsion driven by two motors each. The sizing of the motors would be 50% of the shaft output, 2 x = 450-500KW per shaft.
    No ships service or emergency generators
    Enough battery storage for hotel loads for 8-16 hours. Recharge would be controlled to daylight hours in port. Underway hotel loads supplied by grid off generated power not stored power estimated battery capacity 200-800KW.

    Or
    2. 4 generator sets (all identical) staged to come on line with load demand and share hours. Sizing would be 275-300 KW. There would be two oil bath shafts for propulsion driven by one or two motors each. The sizing of the motors would be 50% of the shaft output 2 x = 450-500KW per shaft in twin shaft set up or in the 2 x = 800-1000KW in single shaft .
    No ships service or emergency generators
    Enough battery storage for hotel loads for 8-16 hours. Recharge would be controlled to daylight hours in port. Underway hotel loads supplied by grid off generated power not stored power... estimated battery capacity 200-800KW/hr rated

    Or
    3. 2 main engines 500-600KW each (identical) driving two shafts with PTO off the transmissions on the shaft output side 1 each 250 KW motor generator combination for either generating power or driving the shaft.
    1 emergency / at anchor generator 100KW
    Battery storage optional

    Or
    4. 1 main generator... (one engine driving two generators 450-600 KW each) with two shafts powered each powered by two motors of 200-250 KW each... or one shaft with a two 400-500 KW motors.
    1 emergency / at anchor generator 100 KW
    Battery storage optional.

    Or
    5. 1 main generator of around 1000-1200KW suppling two shafts with single motors of 400-500 KW... or one shaft with a 800-1000KW motor.
    1 emergency / at anchor generator 100KW
    Battery storage optional

    Or
    6. 1 main engine... driving a gearbox with two 100 KW generators on PTOs
    with one shaft.
    1 emergency / at anchor generator 100KW
    Battery storage optional

    Or
    7. 2 main engines... driving each a gearbox with each a 100 KW generator motor on the PTO
    Two shafts driven off the gearboxes
    1 emergency / at anchor generator 100KW
    Battery storage optional
  13. Innomare

    Innomare Senior Member

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    Karo, to answer that question, we would have to know what you are trying to achieve.

    Are you
    1. trying to save fuel for economic purposes?
    2. trying to save fuel and reduce emissions globally?
    3. trying to reduce emissions locally (in the harbour and at anchor) for your comfort?
    4. trying to come up with an innovative concept to get a subsidy even if it doesn't save any fuel or emissions? (don't laugh, it happens all the time)

    And last but not least, what is your typical usage of the boat (% of time in harbour, % of time at anchor, % of time sailing at reduced economic speed, % of time sailing at maximum speed) and - supposing money matters after all - over which time period would you like to see the extra initial investment recouped (5/10/20 years?).

    Bruno
  14. Yachtjocky

    Yachtjocky Senior Member

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    Nobility

    Nobility has nothing to do ith it, how can you command or tell someone to do something if you have never done it yourself.

    I have never been in the military except as an officer in the royal naval reserve but in the merchant marine either in the engine from or out on deck every officer has served as an apprentice and has learnt his or her way up.

    I would not be where I am today if I had not cleaned out blocked deck toilets while in Bombay 42 years ago. Would I clean toilets today, no way but the person I am aking to do that job certainly knows that I could.

    As for your hypothetical ship/yacht, start off by telling us what you are trying to achieve and then your choice of engines/generators can be chosen for a multiple number of reasons, space & weight being but two.

    Father son configurations proved themselves in some applications while single engine installations are good in others. Single generators with electric motors for each shaft are being tried with battery back ups or using batteries only to leave port for silent running.

    The large cruise ships that have pods with generators are now required to change over to shore power only in more & more ports around the world, next it will be merchant ships.

    Shaft generators both AC & DC have been around for a long time.

    Your hypothetical yacht / ship will have an extremely small market for many years to come, not that I disagree with the way you are thinking.

    PS. I have not cleaned a toilet for 42 years after that experience. :D
  15. karo1776

    karo1776 Senior Member

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    My grandfather's advice had nothing to do with whether you had or could do the work... but with being able to get a crew to work for you. In his case he was not technically inclined but could out work anyone... and could do and had done all the crap jobs.

    As to the DE concept yacht... I think you have to consider it like you were Feadship the F45s or Amels. And, look at it as a pre-engineered package for general yacht service.

    I cannot talk real specifically as to my private use due to not wanting to get upside down with tax authorities. But you would not be far off the mark as follows:
    Per annum
    1000 hrs total use per annum maximum running likely much less
    Primarily family use by 60+ yrs people 3-4 people at a time... 6 would be rarely.
    Some use to put unwanted house guests for a few days... a very few times a year... with short cruise of 1-3 days.
    No long voyages... to the south seas or ever to Arctic or some where like that.
    Berthed in marina most of the time... often day use for a few hours in the afternoon when I want to get away from the house... and don't want to be at office.
    1 or 2 dinner cruises each week during the season in the med.
    2-3 weeks (may be broken up) "vacation use in the Med" maybe once in a while venturing nearby.
    1-3 weeks (usually one trip) "vacation use in the Caribbean"
    No family or guests on crossings...
    Ability for very quiet anchoring out... some places are nearly impossible to get a berth... like Capri for example in season.
    No large parties... no "Grand Prix Weeks"
    2 times a month short trips of 1-3 days.

    Maximum annual expense operating 3 million euro (hoped for)... less berth fees. Never had to consider fuel economy an big issue.
    At least on hauling out per year... mostly two... for maintenance and cleaning.
    Keep 5-7 years... resale not important.
  16. HTMO9

    HTMO9 Senior Member

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    Composition of a DE propulsion

    Speaking in terms of setup of Gensets / electric motors or drives for ship / boat / yacht propulsion, the type of vessel and its usage is most decisive.

    The decision whether a DE setup is choosen or not, might not always be fuel consumption of fuel efficiency. The reason can be the enviroment, noise, vibration, construction or naval architectually based. The DE setup might be less efficient or more expensive, but for some reason necessary or wanted.

    As a ship owner, for a long range, constant speed merchant vessel, I would only choose a DE setup, if dictated by the construction of the vessel. For economical reasons, a DE setup on those type of ships does not pay back. Adding a shaft generator as hybrid propulsion or get me home device, is no contradiction.

    But for a setup with gas turbines for propulsion (like LNG tankers or large high speed vessels, f.e.), I would always choose a DE construction with GTs, because, except for military applications (CODAG / CODOG), driving a generator (for multiple reasons) is the best use for a gas turbine on a ship.

    For a large cruise ships, a DE setup is common practice. It gives much more flexibility with the internal layout and is much more efficient and flexible, because of the large hotel power needed. Here, the common setup is two or three large diesel gensets plus a number of smaller gensets for the hotel load.

    For a large yacht (above 280 feet LOA), when choosing a DE setup, I would use an array of identical gensets (as often done by a well known yard in northern europe), which in size, they would be as small as the normal night hotel load of the yacht (when on anker). The amount of gensets would depend on the power needed for hull speed plus full hotel load plus one emergency genset. The load would be calculated at cos phi 0.8, in order to have some reserve. That means, under normal circumstances, some of the gens are not needed and the used ones run at optimum load. That takes care of all possible profiles a large yacht may have. High speed (for any reason), long range ferry, trolling or loitering, DP mode or just hotel load, when on the hook. But when taking the decision for a DE setup, I would also go for pod drives, like the Schottel SCD plus Schottel SPJ, for true DP capability and the smoothes ride possible. Battery backup for a large yacht (with the technology available at the moment) is not practicable at all.

    For smaller yachts, I would go for a diesel-mechanical setup as long as possible, unless a specific yacht type or usage needs DE. That does not exclude an inovative generator setup for the hotel load or an get me home device.

    Only for much smaller boats in the range of smaller than 45 ft LOA, I would start thinking about DE or hybrid propulsion. Here are systems available on the market, which are proven and reliable. I have seen a 32 ft steel roamer, a 37 feet sailboat and a 42 feet sailing catamaran with DC-DE-hybrid propulsion. They worked flawless and perfectly. But large Li battery banks, IMO are not ready for boat use jet. They are to expensive and to dangerous when mistreated. 2 Volt traction batteries are in my opinion the best batteries for propulsion and hotel load of boats at the moment. They last very long, are very flexible for higher voltage setups and are very tolerable against deep discarge (idiot proof).

    Cheers
  17. Innomare

    Innomare Senior Member

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    On this subject, I think the type of "hybrid drive" from Veth propulsion is an interesting proposition. This was used on an inland container vessel (Semper Fi) built here in Holland last year.

    It uses Veth Hybrid Z-drives. These are pod drives with contra-rotating propellers, which have two inputs at a right angle: one for a direct diesel, the other for an electric motor/generator.

    Veth Propulsion - Project Semper Fi

    The advantage is you have both the efficiency of the direct-diesel drives (no conversion losses going through electric), yet the possibility to drive the pods on generator power with low loads (dynamic positioning, entering the harbour etc.). On Semper Fi, they had four identical generators, but on a yacht - I think you would rather have two larger propulsion engines and two smaller generators, given the big difference between hotel load and propulsion load usually.

    There is also the possibility to use direct diesel and generators together when more power is needed, or to run only the main diesels and use the motor/generators as a kind of shaft generator (allthough this was not implemented on Duandra).

    On the subject of shaft generators: people seem to think that this is "power for free", but it still takes power from your main engine, and when you use the same fuel as on the gennies (no yacht uses HFO), this will probably not even save you fuel (albeit some running hours on the gensets). The biggest limitation is that you have to stick to a certain rpm on your main engines. Most cargo ships running a shaft generator have controllable pitch propellers, to maintain some maneuverability when using the shaft generator.

    Apart from any fuel saving, it's worth to note that on Semper Fi, they have complete exhaust gas cleaning, also for the main diesels, with CRT particulate filters and ureum injection for NOx reduction. Makes you wonder: if this is possible on an inland container vessel, why has this never been done on a megayacht? It may be so that the extra investment doesn't pay dividend with the typical low running hours a of yachts' main engines, but that's a question of doing the math at the start of the project. And surely a cleaner, quieter and more maneuverable propulsion system would justify some extra cost?

    Bruno
    Last edited: May 9, 2013
  18. HTMO9

    HTMO9 Senior Member

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    Thank you very much for that find, Innomare! I will have my R&D departement look into that system. It seems like a good idea for a newbuild.

    Cheers
  19. Innomare

    Innomare Senior Member

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    Inland shipping is worth looking at, that's where most innovation is taking place, because of the strict emission norms coming up (needs to be competitive with road transport, which has cleaned up a lot in the last decade).

    In the past few years, following types of inland waterway vessels have been built in Holland: of course direct diesel, diesel-electric with drop-down thrusters for less ballasting with low load, direct-driven dual fuel (LNG+diesel) with LNG for e-power, hybrids such as Semper Fi and most recently a very promising LNG-electric vessel.

    The problem with the Semper Fi-setup may be that it moves the entire engine room aft, where most yachts now prefer to have a beach club with direct access to the sea. Also, with most (displacement) yachts either sailing at cruising speed or not sailing at all, I think it may not give any reduction in fuel at all, but as said, it's often more a choice for "comfort under certain circumstances" than a "green" choice, which is why I get irritated when I see (serial) diesel-electric touted as the "green solution", when even without doing the math you can see it will only burn more fuel.

    Perhaps people concerned with the environment should shift their focus from the power production (which is pretty efficient with modern diesels and direct-driven propellers, also at partial loads), to reducing the amount of wasted energy and to the cleaning up of their exhausts.

    So contrary to what you might expect, I think for large yachts, Semper Fi is more interesting for its catalytic converters and ureum injection, than for its hybrid Z-drive propulsion system with diesel-electric option. I think she will mostly sail on both her direct diesels, and the good thing about that system is that that option is still there (contrary to a serial DE system). For a yacht, this is even more the case, as there are hardly any different load conditions (no upstream/downsteam and loaded/empty).

    I have to admit, "hybrid drive" sounds so much more sexy than "ureum injection", but shouldn't we let the numbers at the bottom line drive the designs, rather than the marketing lingo? And with numbers, I don't just mean the € or $, but also the NOx, CO, particles and CO2.

    Bruno
  20. HTMO9

    HTMO9 Senior Member

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    I am looking at this project under the commercial point of view, as I am also involved in inland cargo vessels. Taking a larger inland cargo vessel in a DE setup (like the 300+ ft Rhine Vessel), especially when transporting reefer boxes, you may reach a point, where the optimum DE setup (for propulsion) may not leave enough electrical power for the reefer boxes behind. With this system you would not have to compose the DE setup for the worst case, because you have an alternative propulsion.

    I will kepp you informed about our researches.