# Working out the load applied to anchors used to hold a car stationary in a river.

1. Feb 8, 2012

### Tom T

Hi

I am trying to work out the load applied to some anchors used to hold a car stationary in a man made river channel. I know it will be something to do with the surface area and the speed/volume of water. Can anyone help, admittedly I am a practical person not a acaedamic so layman terms please.

Tom

2. Feb 9, 2012

### Tom T

So I have a car side ways on to a flow of water moving around 15mph, I imagine there is around 5 square meters of surface area that the water hits, how much load will be applied to the anchor holding the car in the channel.

3. Feb 9, 2012

### Studiot

You have mixed imperial and metric units, but I am going to work in imperial.

The maximum possible force is larger than you might think and is given by

$$F = \frac{{wa{v^2}}}{g}$$

F is the force in lbs,
w is the weight of water in lbs per cubic foot = 62.4 lbs per cubic foot
a = wetted area of car = 54 square feet
v is the velocity in feet per second = 22 feet per second
g is the acceleration due to gravity = 32 feet per second per second

F = 62.4*54*22*22/32 = 51,000 lbs

Max pressure would be F/a = 944 lbs per square foot or 6.5 psi or about half an atmosphere.

go well

Last edited: Feb 9, 2012
4. Feb 10, 2012

### Tom T

Thanks

yeah its a complicated situation because buoyancy also affects the car, the heavier the car the more friction it is subjected to on the river channel, reducing the load, thanks for you time

tom