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First solar powered circumnavigation

Discussion in 'General Yachting Discussion' started by Norseman, May 6, 2012.

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  1. Norseman

    Norseman Senior Member

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    Just a big panel on the bimini top, probably 180 watts or so, not quite enough
    to "run" the boat, but rather to charge up the 8 batteries between trips.
    The use will be around The Fort Lauderdale canals, New River and harbour area, I hardly go for more than 3-4 hrs now so this rig should be perfect for my use.
    Queit, no fumes, no trips to the gas station and free power..:cool:
  2. SomeTexan

    SomeTexan Member

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    I can understand that. Upsidedown cake=good, upside down boat=bad. You said the motor was rated at 10hp, is that peak or hp at cruise or top speed. Electric motors hp usually drops as the rpm increases. Maybe at 10hp at zero, 5ish at max. Does seem slow unless 6 knots is hull speed.
  3. SomeTexan

    SomeTexan Member

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    That's cool. Hopefully the repair work is minimal and you can be enjoying it shortly.
  4. Chapstick

    Chapstick Member

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    No, no, no.

    Power output at 0 rpm is zero.

    Torque is maximum near 0 rpm, not power.

    Power output for a DC electric motor will be max at around half the maximum torque.
  5. SomeTexan

    SomeTexan Member

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    If there isn't power at zero rpm, then it wouldn't have the power to start turning. So, torque must be power. If hp is zero and torque it at max, that's where the power is. I had an idea that if I posted that you would have something to say.
  6. ScotL

    ScotL Senior Member

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    ......
  7. Chapstick

    Chapstick Member

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    Sorry SomeTexan, but you are completely and utterly wrong. The sentences you've written here are nonsensical.

    You apparently understand neither power nor torque. Torque is not power.
  8. SomeTexan

    SomeTexan Member

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    Outside of engineerland, quite a few people are coming to this way of thinking. You said hp is power, and power is zero at zero rpm in this electric motor. Well, if it has no power available, how does it overcome inertia and resistance to start turning? That's takes power, aka torque.
  9. K1W1

    K1W1 Senior Member

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  10. SomeTexan

    SomeTexan Member

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    With r/c cars back in the day, I have have changed brushes, turned comms. Never messed with brush holders, just the brushes and springs. Had you read, you would have noticed that the electric motor in question belongs to Norseman, I've never seen or touched it.
  11. Chapstick

    Chapstick Member

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    It's not a case of me saying hp is power. That is what hp is: a unit of power. Watts is the metric version. They are the same thing, scaled by a constant. They both are units of energy per second (power).
    When we talk about distance we talk in terms of feet, or metres, or miles.
    When we talk about power we talk in terms of hp or watts.

    At 0 rpm it is outputting no power. (Think about it this way: how many light globes can you light from a generator spinning at 0 rpm?)
    To increase rpm above zero you increase power input - which causes power output to become greater than zero.

    Torque is not power. For your own sake, please go and learn what torque and power are. Ask your engineer friend or your step-father to teach you.

    EDIT:
    Because you like dynos, here is some dyno output, from this page:2012 McLaren MP4-12C: Dyno Tested
    [​IMG]

    At any point we can draw a vertical line through rot.speed(rpm), power(hp), and torque(lb-ft), and see their relationship: hp = rpm * lb-ft / 5252

    For example at 3000rpm: 3000rpm * 260lb-ft / 5252 = 148.5 hp => exactly what the dyno shows

    Or at 7000rpm: 7000rpm * 375lb-ft / 5252 = 499.8 hp

    This relationship is ALWAYS true, for any point on any dyno output.
  12. SomeTexan

    SomeTexan Member

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    You said no hp or power is available at zero rpm, only torque. We aren't talking about the power being fed to the motor, we are talking output. If there is zero power available, there wouldn't be enough power to overcome the resistance from the bearings and the brushes themselves and start turning the motor. Like it or not, there are people trying to get these incorrect rules and definitions updated. These rules you talk about are wrong. There are flaws in them. Once they are corrected we will start seeing real innovations in power and economy.
  13. Chapstick

    Chapstick Member

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    Prepare to be disappointed. Zero rpm means zero power. Or alternatively, if you prefer, zero power means zero rpm. When you you input more power, rpm will rise above zero. These aren't rules. They're descriptions of physics.