Are electric horses really bigger?

Discussion in 'Electric Propulsion' started by DennisRB, Apr 9, 2016.

  1. Caroute Motor
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    Caroute Motor Junior Member

    I mean the low RPM electric motor which is under water. There is no gear box or shaft, the power is directly out. Their efficiency is normally higher than same HP gas motor. But this kinds motor can not make larger HP, just can be used for some smaller boats. Gas motor is still a good choice if engineer can not slove the batteries storage problem.
     
  2. powerabout
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    powerabout Senior Member

    I dont get when you say efficiency higher than the same HP gas motor?
     
  3. powerabout
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    powerabout Senior Member

    well said Gonzo
     
  4. Caroute Motor
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    Caroute Motor Junior Member

    The thrust and boat speed will larger and quicker for same HP, same small boat and same cruising enviroment. I mean HP below 10PH electic motor and samller boat. For large boat, the gas motors still have their advantage.
     
  5. powerabout
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    powerabout Senior Member

    ok I get it as constant torque will assist acceleration
    but if we had a drag race and I carry the fuel and you carry the battery and the boat planes it would be a different story
     
  6. Caroute Motor
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    Caroute Motor Junior Member

    Yes, you are right. It just can be used for cruising. For racing, unless you have super batteries. The battery is still a problem.
     
  7. powerabout
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    powerabout Senior Member

    cruising is worse as you have long term in-efficiency of about 30% than the same diesel input with shaft drive.
    If you can cruise with solar it then becomes a no brainer
     
  8. Caroute Motor
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    Caroute Motor Junior Member

    New techinical will do power management from electric motor's IC. For low HP electric boat motor is not problems now. Like TESLA, it has solved the car's problem.
     
  9. powerabout
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    powerabout Senior Member

    let me know when we have a Tesla truck and down hill water
     
  10. Caroute Motor
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    Caroute Motor Junior Member

    :)That's why I told before it's for small boat, not large boat. Electric boat motor is just a trend for some area. Gas motor is still mainstream.
     
  11. gonzo
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    gonzo Senior Member

    You still haven't justified you claim about higher efficiency of an electric motor. Efficiency is the ratio of power out/power in. Where is the electricity coming from to run the electric motor, and what is the efficiency of its production?
     
  12. kerosene
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    kerosene Senior Member

    Caroute. I am a potential client of your products. I am looking at electric outboards above the typical trolling motors and find torqeedo too pricey.

    Whether its language barrier, marketing person trying to explain engineering - you are hurting your case. When you start talking about the efficiency of combustion engine affecting how effective the horsepowers are you lose all credibility.
    Equally you tout 65% efficiency for your motor while totally messing inputs and outputs.
    If the 65% is for your electric motor its pathetic. If its accounting for motor and controller losses and propeller losses its pretty good. Right now we have to guess. Either way to suggest that gas motor would be 30% efficient from engine shaft (that is where the hp is measured btw. Not battery draw like your marketing numbers) to propulsion is an inaccurate blanket statement. Gas engine can have a well matched prop too...
     
  13. kerosene
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    kerosene Senior Member

    And I am a king of USA just because I say so. Jus saying our HP is more than your HP without explainind why is pointless. Right now the ONLY efficiency benefit I can see is that compared to a gas outboard your motor doesn't need right angle drive / bevel gears. That does not make the difference between 3hp and 7hp...
     
  14. serow
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    serow Junior Member

    I see what you're getting at but i don't think this is quite right. What follows is a guess. A large propeller coupled directly to a small engine may not allow the engine to reach substantial rpm, the engine may stall because it doesn't have enough power at low rpm. Sadly it is not possible to get to high rpm without starting a low rpm. So if for some reason you decided to put an over-large prop on a small engine you would need a gearbox or a different kind of torque converter. I'm not making a great case for electric drive, but my guess is that you could over prop an electric motor and might find that the torque converting characteristics allowed it to turn slowly until speed builds up and it performs as 'advertised', hopefully before burning out, whereas with a small outboard with a too big prop this might stall.So on this basis power for power an electric motor may be able to carry a larger prop and propel the vessel more efficiently at normal running speeds. To compete maybe the outboard would need a high and low ratio.
    I've looked on the Amazon site at this 150# model. If that can really develop 150# bollard pull i should be surprised; the pole looks to small for a start. Image it clamped horizontally with someone standing on the business end.
     

  15. DennisRB
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    DennisRB Senior Member

    Your argument seems to ignore that gearboxes are very normal and only consume a few percent. Comparing a direct drive electric with direct drive combustion is a false dilemma.

    Also you need to understand the power curve required by a propeller. As it increases in speed it needs exponentially more power. Therefore if the engine struggles with it at low rpm it has no chance of even reaching moderate rpm. Even if you gave it a boost somehow to reach higher rpm, it would be significantly more overloaded there not less loaded. With a certain amount of extra rpm, you might get 4 times the available engine power, but the prop might need 20 times the power as its requirement for power rises much more sharply than an engine power curve.
     
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