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How much power is needed to pull 2 persons through water

  1. Jun 18, 2015 #1
    Hey guys,

    I am planning to do a project which can pull 2 persons through water at some speed. For example a casualty and a lifeguard This would be similar to a sea scooter which divers use, however it floats on the water only it does not dive.

    I am not sure whether to post it here or in the differential equation section.

    Is there some kind of equation that I can use? I am looking for an equation which takes the 2 persons into consideration (average) and also you can enter thee seed at which you want them to travel. Hopefully it takes into account the drag as well. The output I want is power in watts so that I can choose the appropriate electric motor.

    Best Regards Glenn
  2. jcsd
  3. Jun 18, 2015 #2


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    Homework Helper

    Perhaps what you need is this equation..

    Power = force * velocity
    or in this case
    Power = drag * velocity

    The easiest way to find out the drag force is to actually tow two people behind a boat at the required velocity and measure the tension in the tow rope.
  4. Jun 18, 2015 #3


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    An excellent suggestion.

    In practice, one may find that the controlling factor is force -- how much grip strength does the lifeguard have on the tow line and on the person being rescued? Paddling a kayak, I can pull 1/4 inch nylon through a swimmer's hands pretty easily.
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