DC Propulsion on semi- planning hull

Discussion in 'Propulsion' started by myastral, Nov 6, 2010.

  1. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    I don't need any information, you are here asking a question or selling something. I am trying to ascertain which. Many people promise many things, but they have no clue how to do the details, like were do you get a megawatt of electricity to power your boat. I am not familiar with any successful diesel electric boats. By successful I mean able to perform even basic functions next to a pure diesel boat. If you have the parts, motors, speed controls,chargers, batteries,generators etc... connecting such in a boat is not difficult. But whether it will fit and work in marine environment is a different story, a planning with its hp requirements is even another story.
  2. myastral
    Joined: May 2006
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    Location: Taiwan

    myastral Pan Asian Yacht Service

    Im a boat builder trying to get information on shafting and props for a higher speed electric boat, I only thought It would be helpful to have some basic details on the system to better explain what information Im looking for and how it would be applied.
    I had hoped that some one else might have been involved with a simmilar project in the past or may be working thru the same issues. It seems I was wrong to ask such a basic detial the way I read it is that Your full of **** if You dont provide all the details and Your selling something if You do provide details.
    I will ask them to remove the post as it looks like it was a rather large waste of time.
  3. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    You have built a bunch of boats, and don't know how to shaft them? What does that sound to you? A boat doesn't care how you get horsepower. The propeller and shafts are dependent on your hp, boat size, design and usage. But you should know that if your a boatbuilder. A lot of people come here and think they have invented a new idea. The problem is the laws of physics are against them. Others are just trying to get peoples moneys for their crazy ideas. Either way don't expect a bunch of real boatbuilders and engineers to allow the impossible to be promoted as fact.

    Moderator - you should leave this post as example to others.
  4. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Well, Myastral, how about giving some more data about your boat, so that the others could make few calcs and give you some useful info?
    The only thing you said so far is that it is 71 ft and semi-planing. That's close to nothing, mate.

    You should provide some more info, like:
    - WL length
    - WL beam
    - draft
    - displacement - empty, full
    - required speed
    - required range
    - intended use
    - river, sheltered, coastal or open-water cruising.
    Without these, it is impossible for the rest of us to help you.

  5. mark775

    mark775 Guest

    I was gung ho about this a few years ago and researched, actually talked to dozens of people that had tried it or were in the process. Visited a Canadian company that was installing Glacier Bay's system. Talked to the guy that was buying the Canadian boat and talked to a salesman that was supposed to be promoting the boats like in the picture on this PDF. http://www.sea.siemens.com/us/inter...m/General/Docs/ELFA_Overview_Presentation.pdf He told me "Don't, under any circumstances try this." He added, "The joke around here is to ask How many German engineers does it take to carry enough extension cord to run these boats" or something like that (they are AC). He said that they were going away from it, yet the Siemens site says (Don't get me wrong - Siemens is a great company and on the cutting edge of technology in many, many ways) something like "nearly 8,000,000 operating hours and no maintenance."
    I wanted to do this in the worst way on my boat (40' semi-displacement lightweight) and could find nobody that had successfully done it. Glacier Bay was full of "forward looking" statements about their DC system but could not supply me with a "product for your application at this time". Maybe Siemens got the bugs worked out on those "trawlers" like on the PDF, I don't know. If you can carry enough battery, get everything to work right, and get reasonable fuel burn out of a micro-turbine (HA - I've been down this path, as well!), more power to you. I'm trying to interact with animals and not alert them and would still switch out my reliable, efficient diesel engine if an electric was feasable. Maybe I'll come buy a system from you!
  6. Yellowjacket
    Joined: May 2009
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    Location: Landlocked...

    Yellowjacket Senior Member

    As others have noted, the energy balance doesn't add up. In order to push a typical 72 ft semi-planing hull you are going to need a lot more power than you are talking about. A typical 72 ft displacement hull has 400kw of power (2 x 200kw engines). You are going to need probably three or four times that much power to get anywhere near a typical semi-displacement speed, and you don't have that much generator power available. If you dip into the batteries for a few minutes you can probably do it, but after 15 mintues you are out of juice and back to displacement speeds.

    Hybrids make sense in land vehicles that are used in stop and go environments since you can recover energy lost in braking and the time average power demand is low. A boat is just the opposite, there is no opportunity to recover power with regenerative braking, and the time average power demand is high. This is why hybrids are a dumb idea in a boat. The only place they might make sense is in the application that mark775 was talking about, the need to cruise quietly at low speed for a limited amount of time. To make a practical semi-displacement boat in this size class you likely need two 800kw engines or more even if they are turbines and are much lighter than diesels.

    Your selection of what are essentially the Capstone microturbines is also a problem. There are very few users that will ever achieve 70,000 hours on these engine because of thermal fatigue of the heat recovery systems. If you turn on the engine and don't turn it off and run at a constant power it will run for a long time sitting on a slab in Iowa, but in the real world, in a boat, there are limitation on life related to thermal cycles of the heat exchanger and bearing life in a salt water environment.

    In a boat, where you might run for a few days at a time at the most, (and more typically just hours at a time) the heat exchangers will more likely be cracked and leaking in fewer than 20,000 hours. Users who run the engine as a prime power system typically see about 40,000 hours of use before teardown, and that is running the engines for a high percentage of the time.

    Also those heat exchangers don't have a way to be cleaned so buildup of salt results in a degredation in performance over time. Before they crack and leak, the performance will fall off due to salt buildup in the heat exchanger. Finally, the bearings in these generators are air bearings. Air bearings heat the air in the bearing and if there is a high salt content in the air, the salt will contaminate the bearing and things will come to a screeching halt. There are also other issues with air bearings having to do with shock resistance that make them a poor choice for a higher speed marine application.

    Operating a 400 volt battery system in a pleasure boat is IMHO a bad idea. That much voltage will instantly kill anybody who gets across the terminals, and can lead to a fire or explosion if a cable shorts out. I know high voltage power systems are used on commercial boats, but there are qualified ships engineers who can oversee the system and understand the dangers of these kinds of systems where a typical boat crew simply does not have the knowledge and experience to deal with a system like this.

    I wish you all the luck with your boat, but when the cost of these generators is considered (about $1000/kw when installed) and the limted power available, this appears to be more of a feel good "green stunt" than a practical boat. If you want to putt putt up the intercoastal water way at displacement speed and tell everybody you have a hybrid and you are "green" then go for it. Other than that I see no practical purpose for such a system.

  7. apex1

    apex1 Guest


    nicely summed up.


    The boat shown in the Siemens leaflet, does not longer carry this burden over the blue ocean! Both, the builder as the owner have finally understood that they shot themselves in the legs.
    The so proudly promoted N-hav.. Hybrid was ripped out of both boats for a hell of a lot of extra money.

    So much on that.

    Not that such setup, which was not a true hybrid, can not be a sensible alternative in some commercial applications, but on a yacht it still is just expensive ballast.

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