Diesel/electric engine for big cat

Discussion in 'Hybrid' started by guerreiroazul, Jul 18, 2010.

  1. Alik
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    Alik Senior Member

    Agree, depends on direction; but one can't just drift (not able to control the boat), can't sail there either. Waiting for wind/current change - good idea... :)

    Diesel-electrical - agree, so how many kW one needs to push big cat in head wind, at least 6kts? Say, 50kW Kohler genset weights 1100kg. Diesel of similar power weights much less... It is cheaper to use diesel.

    It is widespread myth that with electrical propulsion one needs less power. Still one needs 3-4kW per ton of displacement just to move the boat...
  2. capt vimes
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    capt vimes Senior Member

    this is absolutely not the point i tried to make...

    on a cruising sailing yacht where you go under sails for lets say 90% of the times and the main engine is used primarely to charge the batteries for weeks and months - be on the way or at anchor - a generator makes simply more sense...
    and for the 10% you are running under motor it is not a big loss if you use el motors to drive the prob...

    everything comes down on the purpose and the intended use of the yacht...
    a globetrotter to live aboard has different requirements then a weekend sailing ship which is motored from the marina to the next bay and back in the evening... with the sails up for probably only 30% of the time...
    here a D/E propulsion would be a waste of money - agreed...

    when on the other hand 80% of its running time the main diesel is only used to charge batteries, i think THIS is a waste of money and resources!
    and if the performance under motor, for the 10% of time where its used, is less then with a proper diesel - who cares...
    it is a sailing yacht to sail with and not a motoryacht... ;)

    another point:
    el motors are working at lower revs - lower revs at the shaft gives you the opportunity for more efficient probs with wider diameters - more efficient probs allows for less kW at the shaft and still keep the same performance... ;)
  3. apex1

    apex1 Guest


    none of the commercial vessels have that.

    Only Cruise Ships, due to their high Hotel load.

    Icebreakers, due to the high torque at low speed. (bearing with the insane inefficiency of the system)

    Few harbour tugs, for the same reason as Icebreakers and with the same penalty to pay.

    The entire merchant fleet is propelled by one single Diesel engine only.

    Wrong again! The KW required are the KW required! No matter how they are supplied. Of course a larger wheel can provide higher torque at lower RPM, but that does not mean you can skimp on power.

    Do a bit of homework or go a few weeks to sea, before contradicting! (much better, leave it)

    edit: sorry came out a bit harsh, was not meant to be........

  4. Alik
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    Alik Senior Member

    This is partial true. Yes, You can use bigger props, but how big they can be? Can they exceed the draft? :) In practice this works only at idle speeds; once You are looking to push boat to weather or run it at required speed (1.8*LWL^0.5) this advantage does not count anymore.

    I did sample calculations few years ago: big props work only at 3...4 kts for 40' boat.
  5. capt vimes
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    capt vimes Senior Member

    all of my statements came from a sailors viewpoint... because i am one.
    so - sails are the main means of propulsion and everything else is... helpfull? nice to have? comforting? required by law!...
    my opinoin in general:
    if u cannot get out of a situation by ur primary means - get stuffed! ;)

    you mean with "high Hotel load" the need for electricty all the time?

    a sailing yacht does need the power when?

    sorry - to my knowledge all the commercial fleet has swaped already... i was mistaken obviously... or could it be that the merchant fleet is still facilitating old ships?

    i will do... ;)

    nevertheless - if your main power is the sails (i am an sailor!) and the other 'thing' is nothing more then an auxilliary (proper spelled?) to me... why should
    i be bothered with 'power-considerations'?
    i want to have my batteries charged - thats it!
    i want to have my auxilliary drive to go into a marina (because u have to use it that way... under sails - forbidden!)
    i want to have my auxilliary to enter shallow, unknown bays...

    do i need to have 'endless' power for that or anything which is capable of driving me against a 10kt current?

    what i do not want to have my auxilliary drive for, is charging my damn batteries most (actually its the majority) of the times!

    and please, try to think that through from a sailors viewpoint - leeshore?
    you made a freaking, motherfuck****, big mistake before that....
    it is your fault, and if you think, yuo can propel yourselves out of this by means of an auxilliary drive... byebye and farewell! :)
    and who says that an D/E propulsion does not provide the same performance?
    there are losses - granted! but who cares?
    its in the word 'sailor' - the one who goes with sails... (ok - i made that one up.. ;))

    you are a motorboat guy... i am not - and i do not see the reason for having an 'powerfull' main drive on board, when the only usage of it, is to charge my damn batteries?
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  6. apex1

    apex1 Guest

    I am a motorboat guy yes. That does not mean I don´t sail.

    A small 1kva Honda is a probably proper solution btw.

  7. Alik
    Joined: Jul 2003
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    Alik Senior Member

    2capt vimes:

    When I was '100% sailboat guy' and sailed only dinghies I never considered using engine as well :) My mind changed once I found myself on board of 87' multihull, with huge windage and limited windward performance.

    Here I discuss some points on electrical propulsion, and give reference to good publication by Nigel Calder in PBM:
    http://www.amdesign.co.th/Contact/Sea yachting_JAN-FEB 2010_2.pdf
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    FAST FRED Senior Member

    you are a motorboat guy... i am not - and i do not see the reason for having an 'powerfull' main drive on board, when the only usage of it, is to charge my damn batteries?

    Lifestyle , these days electric is a requirement.Radio, Freezer , auto pilot , just to name a few.

    The ONLY hassle with using the propulsion engine as a gen set is the common set up was Optimized for propulsion.

    For a few more bucks the same propulsion engine could be optimized for use as a DC power plant.

    A pair of 24V 300A coach alternators (if needed) would be a good way to pump batteries back to full.

    They would have to be a quite large set to use 600A as the charge amperage is usually only 20% of the batt bank cap do the batts would be 3000A (and close to 3000lbs) .

    Fancy spiral wound batts with real good temperature monitoring and perhaps water cooling could load the propulsion engine to 80%+ of its rated load , and be efficient .

    The good news with big alternators is the loads on the engine could be set to be high (and therefore efficient) even as the charge load and RPM go down.

    This would give the "best" of both worlds , a vessel that can cruise well (SL 1.2) on its aux diesel with outstanding range, and a charge system that is dedicated to DC battery charging , and can refill the house set in as short a time as one can do, today OTS.

    For in and out of docks noiselessly, the electric trolling motor from the outboard would work fine.

    Tho it might make more sense to put it on a bracket at the bow , and use it as a bow thruster most times.

  9. DougCim
    Joined: Jul 2010
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    DougCim Junior Member

    I have seen from earlier threads where people suppose that since so many trains use a diesel-electric setup, that it might be a good thing for a boat's main engines. It's generally not, but you need to understand the reason that trains use them to know why.

    Trains have a unique engine requirement among vehicles, in that a train locomotive needs maximum engine torque at zero wheel RPM when the train is trying to start rolling. There's only two types of engines ever developed that can do that: external combustion steam engines and electric motors. There's never been any mechanical transmission that can do that. There is nothing else that is considered workable.

    There's never been any way to make batteries that could store as much energy as the same bulk/weight of liquid fuel, so when train builders wanted to try using big electric motors instead of steam, they hooked up the most-efficient (diesel) engines they could to generators, and used the electrical power to run electric wheel motors.

    What drove steam locomotives out of use and ushered in diesel-electrics was not that the diesel-electrics were much more efficient; the overall fuel costs for each were fairly close at the time they co-existed. What killed off steam locomotives was that compared to the diesel-electric engines, the steam engines required relatively frequent and expensive maintenance.

    So now you see,,,,,,, trains use diesel-electric, only because it can deliver VERY high torque when the train is at zero MPH, and is lower-maintenance than steam. There is always a double-loss converting the engine power to electric and then back to mechanical--but with the diesel spinning at its ideal RPM for power, the whole setup still puts more zero-RPM torque down for less overall cost than any other engine/drivetrain setup can.


    To clarify--I am not arguing with what CDK or Apex said, I am agreeing with it.
    Unless you require high torque at very-low RPMs, a hybrid drivetrain is almost always going to be less efficient overall than a regular internal-combustion engine connected mechanically to the load.
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  10. apex1

    apex1 Guest

    A valid argument.

    Closer to marine applications than the locomotive propulsion is the Icebreaker mentioned above. Extreme high torque requirement at very low, to zero speed.

    There we have a similar situation and the same solution. Steam or D/E is the sensible way to go.
    The steam engine still is absolutely competitive in terms of efficiency, in some cases even the better choice! In predictable ice conditions the steam production can be very fine tuned to meet the demand. A Diesel has to run at his fixed rpm regardless of demand.
    And the steam engine produces higher torque than any other propulsion.
    The old 2000 hp/i steam Icebreakers have had the same performance as their 8000 hp successors!
    And believe me I know what I am talking here, I operated both systems from stoking, to commanding them.

    Steam engines fell out of duty for several reasons.

    First was the labour cost and unbelievable hard conditions for stokers.
    A train can change personal at every station, but on a ship you need three shifts of stokers and trimmers!
    The engine mentioned needs at least 3 engineers / oilers to be run, in three shifts again.
    Thats 9 stokers, 9 engine men and a chief and a second. 20 people!
    The D/E does with 4.

    Second the weight penalty. A 2000 hp/i engine has a weight of about 90 tonnes. The steam specific auxiliaries bring another 20 - 30 tonnes in. The boilers in this example additional 200 tonnes operational.
    Thats about ten times a rugged Diesel Electric setup!

    Last the maintenance, which is not soo much in favour of the D/E as one would assume, but noticeable of course.
    A professionally operated and serviced steam engine outlasts every other system by centuries and has not much wear and tear except for the bearings, which are replaced fast and cheap.

    The link Albert provided above is a good one and especially the Nigel Calder article in ProBoat.

  11. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Well said Richard.

    There is one more reason to use D/E in locs. The traction is divided over several axles due to the wheel-to-rail friction limitations. It would be very complex to do that mechanically. Furthermore, electric drive units are more or less standard components for trains, so the D/E choice is a logical one.

    For the icebreaker a designer who hates electricity (purely hypothetical of course, why should someone hate that) could use a hydraulic torque converter.
  12. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    Here's another repost of an old post of mine,people who were promised that an electric motor with a fraction of the hp of their old propulsion,was the same due to lower speeds and more torque...:

    The builder / owners of a Wharram Tiki 46 catamaran recently removed their 2 x 25 HP electric motors, genset and electric drive batteries. Here's their analysis of electric auxilary propulsion on KittyWake:

    As some of you may know, we have 2 electric motors in addition to the outboard.
    There is one hanging between the skeg and keel on each hull.

    ************We are way underpowered by these and their only usefulness is with docking maneuvers.***************

    They also make a ton of noise as the props spin so that even when we’re just sailing we hear motor noises which is quite irritating.

    To reduce the noise we’ve considered removing the props, but then the motors are really just added weight and drag. We also tried turning them just slightly on to the recharging setting to stop the prop spin, but then noticed that even with only one motor on our speed decreased by almost a knot. Unacceptable.
    Now we have our work cut out for us removing these motors and repairing the hull.

    After removing the electric motors KittyWake notes the following:

    The motors are gone. The hulls look so sleek right now without those blobs hanging underneath. Now we are debating what to do about the 48 volt generator. It’s been up on Ebay for a few days but like all the other generators listed, there are no bids. We did post 6 of the batteries on Craigs list tonight and within a few hours already had them sold. Hopefully the rain will stop so we can patch the holes tomorrow.

    And we actually got to sail for a while. The sound of water rushing past the hulls was, well, the only sound. Exactly as it should be. I’m really glad the motors are gone.

    KittyWake's blog: http://kittywake.us/
  13. MatthewDS
    Joined: Mar 2010
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    MatthewDS Senior Member

    Relating to Icebreakers, I took a tour of the USCGC Healy last week. She is the largest US Coast Guard Icebreaker in operation.


    Several things stood out, relating to this thread. First, she is powered by 4 diesel generators, each about the size of a shipping container. I don't recall the combined horsepower, but it was tremendous.

    Secondly, they had a direct video feed from the shaft to the bridge, so that the prop rotation could be monitored visually. I think this backs up Apex's comment about icebreakers needing extremely high power at low speed.

    Very interesting all around, but I can't imagine using a hybrid system unless there was a very specialized need for it. ( Such as ice breaking )
  14. WestVanHan
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    WestVanHan Not a Senior Member

    I think maybe another good reason is when they are breaking thick ice,they can only break short distances at a go-so are often continually going back and forward.

  15. apex1

    apex1 Guest

    That is not common. The usual way is to move at a continuous pace forward. Ramming is not successful and only stresses the material.
    Icebraking is nothing but moving the weight on the ice surface to break it.


    Icebreakers have NO HYBRID system! That is plain, simple Diesel Electric propulsion.

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