# Human Horsepower on the Water

ForeverSwim
Pittsburgh, PennsylvaniaCharter Member

I was curious the other day, after racing a low-power boat at Keystone Lake, how much horsepower a swimmer could generate on the water. After briefly researching this topic, I found out that the UCLA Physics department was able to calculate the output (horsepower) of a human, by timing (seconds) the human (weight) up a flight (distance) of stairs.

The calculation is as follows:

Weight (lbs) x Distance (feet) / Time (seconds) X 1/550ft-lbs-sec (1hp)

If this were the case, I figured that I would like to see how much horsepower a swimmer could generate over a shorter distance as well. I thought a 25-yard freestyle sprint would make for the highest amount of output (horsepower). I used my personal statistics as an example:

225 (lbs) x 75 (feet)/10.5 X 1/550 =

16,875/10.5 X 1/550 =

1,607.14/1 X 1/550 =

1,607.14/550 = 2.922hp

In conclusion, a 225lb person, swimming 75 feet in 10.5 seconds would generate 2.922hp. I cannot say I am a physics scholar, so please let me know if I am wrong in assuming the length of a pool would be the same in this calculation as the flight of stairs!

Just thought everyone would enjoy this calculation!

The calculation is as follows:

Weight (lbs) x Distance (feet) / Time (seconds) X 1/550ft-lbs-sec (1hp)

If this were the case, I figured that I would like to see how much horsepower a swimmer could generate over a shorter distance as well. I thought a 25-yard freestyle sprint would make for the highest amount of output (horsepower). I used my personal statistics as an example:

225 (lbs) x 75 (feet)/10.5 X 1/550 =

16,875/10.5 X 1/550 =

1,607.14/1 X 1/550 =

1,607.14/550 = 2.922hp

In conclusion, a 225lb person, swimming 75 feet in 10.5 seconds would generate 2.922hp. I cannot say I am a physics scholar, so please let me know if I am wrong in assuming the length of a pool would be the same in this calculation as the flight of stairs!

Just thought everyone would enjoy this calculation!

www.darren-miller.com Pittsburgh, Pennsylvania U.S.A.

## Comments

Generally:

Power = 1/2(density of the fluid)(velocity cubed)(reference area)(drag coefficient)

Which is also why it is much more efficient to maintain a constant speed while swimming. It just requires less power. Remember it's velocity to the 3rd power!

evan.marathonswimmers.org

@evmo, funny, I never actually used one of those things, however we did do the "stretch cords", which were the rubber tubing-block-swimmer devices. I wish I would have, might have made me more of a meat-head than I am today ;)

www.darren-miller.com Pittsburgh, Pennsylvania U.S.A.

Power = Force x Velocity

Force = (1/2) x (density) x (velocity)^2 x Drag Coefficient x Area

Assume: Drag Coefficient = 0.5, velocity = 2.27 m/s, Area = 0.15m^2

Power = (1/2) x (1000 kg / m^3) x (2.27 m/s)^2 x (0.5) x (0.15 m^2) x (2.27 m/s)

Power = 438 Watts

Power = 0.58 hp

evan.marathonswimmers.org