1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    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


    User Avatar
    Science Advisor

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook