Turbines and electrical propulsion for a schooner

Discussion in 'OnBoard Electronics & Controls' started by james.smith, Mar 19, 2016.

  1. james.smith
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    james.smith Junior Member

    Jamie, hi,

    > The weight of the batteries is also a limiting factor...

    On a vessel of Cecelie's size? I think you'd need a good few tonnes of batteries before this became an issue.

    > If you can reduce your cruising speed requirements, when operating without wind...

    I think there's a misunderstanding here. The propulsion system, whether electric powered or whatever, would be used for manoeuvring only. Cecelie is a sailing ship.
     
  2. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Would you not use some power in very light winds, or no winds. In very light winds you can greatly increase what you get out of the wind with a relatively small amount of power. This is easier with a controllable pitch propeller, but with a CPP you also gain maneuverability, and efficiency over a greater range of speeds.
     
  3. Stumble
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    Stumble Senior Member

    How many days can you afford to be becalmed, and what do you do about it when you are? I have crossed the Gulf of Mexico in zero wind the whole way. Sure you could just sit there for a week waiting on breeze, but few are really willing to do so.
     
  4. Jamie Kennedy
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    Jamie Kennedy Senior Member

    I'll bet with the right propeller you could move along fairly good with just a 100 HP diesel running in it's sweet spot at 50% full power. That would be enough to turn a breath of wind into a breeze. With two 50 HP diesel engines you could run just one of them at 25 HP, give the other a rest, and let the wind do most of the work. If these were diesel generator setups, you could be tapping off what you need for house power and use the same two engines for everything, including your bow thrusters and whatever else. There would be conversion losses compared to a transmission, but because it is a low power motor sailor the losses are smaller. Not sure how easy it is to find a controllable pitch propeller of the right size. Does the bow thruster really need to be that huge? Maybe two controllable pitch propellers, and no bow thruster?
     
  5. gonzo
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    gonzo Senior Member

    Rastapop:
    The link to that article says that the Navy started the study in 2008 when a barrel of oil was $174. It is less than $42 nowadays. That will nullify any savings. Also, the Navy has a dedicated, highly trained crew of technicians to run the system. A group of amateurs are not likely to keep it running correctly. Further, these are high speed vessels that would have an HED system for low speed operation. The vessel in this post is always operating at lower speeds. A variable pitch propeller would be a much better investment.
     
  6. Rastapop
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    Rastapop Naval Architect

    And it also says they're going to start installing them this year. Could it be that UK Navy's financial assessment is inferior to yours?

    I don't why you assume they use oil anyway. If it did it would be a pretty unusual modern destroyer.

    What group of amateurs? You didn't limit your comments to diesel-electrics run by amateurs, you made them about diesel-electric in general - and you made them about efficiency, not maintenance.

    The statement "diesel propulsion is more efficient than diesel-electric" is not correct. For some vessels it's true, and for some the opposite is true.

    If only the UK Navy had thought to employ you to give them better advice than all their naval architects can!
     
  7. gonzo
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    gonzo Senior Member

    Your sarcasm aside, I pointed out that it works for the Navy where the only consideration in this case is fuel. They don't make any claims that the overall operational cost is less. For commercial and private vessels, the overall cost is the driving motivation. Also, my comment is for this post and not "in general" as you claim. The context of a post is the thread it is in. Lowering yourself to personal attacks does not strengthen your arguments. If you disagree, show data instead of insulting me.
     
  8. Rastapop
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    Rastapop Naval Architect

    Your post says EDIT:<gearbox> losses are less than hybrid losses, and ignores engine losses. That isn't specific to this thread only.

    The Navy is going hybrid "in a bid to lower fuel costs". (Read a little more carefully.)

    Unfortunately when I provide links you claim you know better than they do, and that they're wrong.

    Again: for some vessels conventional diesel is more efficient, for some vessels diesel electric/hybrid systems are more efficient.
     
  9. gonzo
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    gonzo Senior Member

    The engine losses are the same whether it is turning a propeller or a generator. I never claimed to know better than they do. That is totally untrue. The fact is that the Navy has crews trained and paid with tax money and it doesn't enter into the cost equation. They are only considering the fuel savings of a high speed vessel (from the link you posted) operating far below their optimal speed (again from the link you posted). Those operational parameters can not be compared to those of an auxiliary sailing vessel powered for harbor maneuvering and providing power for house use. Perhaps you should read the links before posting them and then engaging in personal attacks.
     
  10. Rastapop
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    Rastapop Naval Architect

    Wrong of course.
    A generator in a diesel-electric will be running at peak efficiency.
    The engine of a diesel propulsion vessel that would benefit from diesel-electric will often be running at an rpm other than peak efficiency, and so engine losses will be greater.

    You said "That will nullify any savings." and "A variable pitch propeller would be a much better investment."

    I feel extremely comfortable assuming that the UK Navy in fact has far more expertise in both finance and naval architecture than you do, and that you are wrong in both statements.

    If you want to have a discussion on that by all means start it, and I'll likely participate.
    But this conversation is me pulling you up (again) and correcting your claim that diesel-electric is less efficient than diesel.

    For some vessels it is, and for some vessels it isn't.

    Of course. As I have repeatedly pointed out, when diesel-electric/hybrid beats diesel in efficiency it's because the vessel would otherwise spend significant time running their main engines at less than peak efficiency.

    And I've made no such comparison.

    I've come to this thread and corrected your incorrect, blanket, non-vessel-specific claims that diesel is more efficient than diesel-electric.
     
  11. gonzo
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    gonzo Senior Member

    You are again taking parts of my statements and creating a false statement. It is a lie that I claim a variable pitch propeller would be a much better investment for the UK Navy. It is a better investment for the OP. Stop all this nonsense and give any advice, if you have any, to the OP.
     
  12. Rastapop
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    Rastapop Naval Architect

    True, I can see that, I missed some context, my apologies.
    Apparently it's only financial analysis you feel capable of advising the UK Navy on.

    Anyway, your ability or otherwise to advise navies is of no interest to me, it's just amusing. I listed the two sentences only in response to your post, it's not the point.

    The point is, again, that despite what you seem to keep claiming around the forums diesel is not more efficient than diesel-electric. (In this thread specifically that only gearbox losses need to be held up against diesel-electric losses)

    It is more efficient for some vessels, and for some vessels diesel-electric is more efficient - because those vessels need to spend significant time with their engines away from peak efficiency rpm.
     
  13. gonzo
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    gonzo Senior Member

    Take a chill pill dude and stop lying. Unless you can name the post where I allegedly advise the Navy, admit to yourself you are lying and move on. Stop hi-jacking threads with your nonsense.
     
  14. Rastapop
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    Rastapop Naval Architect

    The UK Navy thinks it'll save fuel with this. You financial analysis though is that oil prices will "...nullify any savings." in post #20.

    I notice you don't mention efficiency. Efficiency is where you made your incorrect claims, and efficiency is where I corrected you.

    Diesel-electric/hybrid is less efficient than diesel for some vessels, and more efficient than diesel for some vessels (because of engine losses).
    Get used to this fact, it isn't going away.
     

  15. DCockey
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    DCockey Senior Member

    Let's go back and read the article about the "Hybrid Electric Drive"http://news.usni.org/2015/09/23/navy-set-to-install-hybrid-electric-drives-in-destroyer-fleet-staring-next-year system being installed on some US Navy ships.

    The original propulsion system remains with the addition of an electric motor which can also turn the shaft. Nothing about any modifications to the existing reduction gear or shaft. The electric motor will be used in place of the gas turbines for power at low speeds where the gas turbines are inefficient. The gas turbines will be used at high speed.

    This is a parallel system where either the electric motor or the gas turbines can turn the shaft.

    It is not a serial system where the prime mover (Diesel engine, gas turbine, etc) is not mechanically connected to the shaft, but rather powers a generator which supplies power to an electric motor which turns the shaft.

    No mention of any batteries being installed to store electricity to power the electric motor. My guess is the ship already has a large Diesel or gas turbine powered generator installed, and sufficient electric power is usually available to also power the electric motor. If the output of the generator set is needed for other purposes then the electric motor the propulsion gas turbines can be used for propulsion instead.
     
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