How much power is needed to pull 2 persons through water

[glenn0010]

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

 

[CWatters]

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.

 

[jbriggs444]

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.

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.