Electric Hydrofoil Powerboat

Discussion in 'Boat Design' started by intrepid71, Dec 28, 2015.

  1. WestVanHan
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    WestVanHan Not a Senior Member

    I am by no means an expert on Li but I know how to read.
    My weight is correct then, but like I said-it depends on how they are counting..do they have 40 kwh of useable power or is it just a 40 kwh pack?

    But it seems the battery pack is actually 40 kwh in total before any discharge,if Li batteries are fully discharged their life does shorten considerably. So in agreeing with Kerosene to prolong their life,discharge to about 70%...which is about 28 kwh of useable power.

    Probably just a pump and dump scheme,or a way to get grant money from governemnts.

    Also FF is correct,I was going to mention but forgot,Tesla makes much money from carbon offsets from other car makers,and sells electric cars incentivized by government tax refunds on EVs.
    https://www.teslamotors.com/en_CA/support/incentives
     
  2. kerosene
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    kerosene Senior Member

    and so far tesla has not made profit ever afaik.
     
  3. Joakim
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    Joakim Senior Member

    Li batteries can handle 500-2000 100% cycles so using the whole 40 kWh does not shorten their life considerably and a 100% cycle is very likely used for calculating the range. It's more of problem that you really need to leave 30% of the capacity unused, since you need some safety reserve to get home.
     
  4. kerosene
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    kerosene Senior Member

    "
    Table 2 compares the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. All other variables such as charge voltage, temperature and load currents are set to average default setting.
    Depth of discharge
    Discharge cycles

    Table 2: Cycle life as a function of
    depth of discharge
    A partial discharge reduces stress and prolongs battery life. Elevated temperature and high currents also affect cycle life.
    100% DoD, 300 – 500
    50% DoD, 1,200 – 1,500
    25% DoD, 2,000 – 2,500
    10% DoD, 3,750 – 4,700

    "
     
  5. Stumble
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    Stumble Senior Member

    They may not be making a profit, but they are cash flow positive. The difference is they are pouring any income into building infrastructure which means they aren't realizing it as profit.

    In the same way Amazon hasn't made much of a profit in its history either. They a) reduce prices to drive market share and b) reinvest in infrastructure for the next round of products.
     
  6. intrepid71
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    intrepid71 Junior Member

    Well they probably need most of their 56 hp to get up on the foils. After that maybe they can throttle back to 12 hp to maintain a cruising speed of 25 knots.

    One interesting design feature is the double foils forward. You don't often see that for fully submerged foil design. I am guessing they needed to get the wetted surface area down to have a chance at making the 40 knot top speed. The double foil arrangement provides the ability to get that upper foil out of the water at the highest speeds, which would greatly reduce the wetted surface area.
     
  7. Turnpoint
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    Turnpoint Junior Member

    I really like that someone is making the attempt... electric boats are definately the future.
    The hull shape does not make much sense to me though. I think it has more to do with what people expect a performance powerboat to look like. Just a guess but take off speed is probably around 14 to 17 knots and that hull shape would need a lot of power to get to that speed. This is one big advantage of an electric drive is that it can easily put out 3 times it's rated hp for quick bursts and help it power up onto it's foils. It also might explain the double foil in that it might be needed to get the boat on foils as soon as possible. But with the hull shape you are putting all your eggs in one basket ie if you could not foil you could be stuck at 8 knots with drastically reduced range. In this regard a slender multi hull with a displacement hull would make a better hydrofoil platform in that it can more easily reach take off speeds and is still efficient when not on foils and at sub foiling speeds.
     
  8. Joakim
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    Joakim Senior Member

    When you take the same amount of energy you need 2x cycles from 50%, 4x from 25% etc. That the table becomes

    100% 300-500
    50% 600-750
    25% 500-625
    10% 375-470

    So ~50% may be the optimum, but 100% isn't worse than 10%. And you get plenty of those 100% cycles. For that boat you could do at least 300*60 M = 18 000 M. It would probably be more than 20 years with that kind of boat and 20 years is about as long as lithium batteries are predicted to survive with little use.

    Also the given 300-500 is a very low value. E.g. Torqueedo claims 800 100% cycles for their battery: http://www.torqeedo.com/en/products/batteries/power-26-104/2103-00.html
    And this article shows several thousands 100% cycles: http://www.saftbatteries.com/force_...ry_life__TechnicalSheet_en_0514_Protected.pdf
     
  9. Heimfried
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    Heimfried Senior Member

    As far as I understood several publications about Li batteries, the 100% DoD is not a characteristic of Li cells in a chemical or electrophysical sense. It is just defined in this way because the built-in electronic control unit interrupts the current before the cells are damaged by deep discarge.

    The link to the specifications of the torqeedo Li battery you posted above, shows manyfold "computer" control of every of the 336 cells of which the battery consists.

    I'm not sure that all manufacturers of Li batteries are defining the energy capacity (100% DoD) in this way.
     
  10. OzFred
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    OzFred Senior Member

    Under company it claims the engine is 60 to 100hp (45 to 75kw), a claim also made by Gustav Hasselskog in this interview (at 11:40). A very interesting system, the foils seem to be computer controlled as well so something else to consume power.
     
  11. kerosene
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    kerosene Senior Member

    Torqueedo specifically states useful capacity so it can be used to that 100% naturally.

    They are not using 100% of nominal cell capacity - in a sense they are more honest than others (most) who list theoretical capacity.

    In fact this only proves my point.
     
  12. Joakim
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    Joakim Senior Member

    So they are saying it has a 2797 Wh capcity, nominal voltage is 25.9 V and nominal 108 Ah. Well 25.9*108=2797. And they also say it has 36 cells with 2.25 Ah capacity and 3.7 V nominal voltage. 36*2.25*3.7=2797 as wel.

    So doesn't 100% mean using 2797 Wh or 108 Ah? Aren't they using the nominal cell capacity they give?

    Or are you saying some other manufacturers would claim a higher capacity for that same battery? So they would include the not meant to be used capacity below say 2.7 V/cell?
     
  13. kerosene
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    kerosene Senior Member

    I couldn't find source now, but i have understood that torqeedo specifically states "in use" capacities vs. pure cell factory ratings. I might be wrong though - even that has happened.
     
  14. gonzo
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    gonzo Senior Member

    It depends on what you call 100%. The formation cycle is the initial reaction and it is non-recoverable. That is about 3-5% depending on the chemistry. There are many different types of Lithium Ion. They are formulated for high capacity, fast charge, etc. We are mainly experimenting with low temperature capacity, which ha been the major downfall of Li Ion batteries.
     

  15. Heimfried
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    Heimfried Senior Member

    336 cells, not 36 cells.
     
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