Buoyancy Formula for Hold-Down Weight

Easy. The weight of the tank empty has to exceed the weight that is expressed by the gross volume of the tank were that volume occupied by water. That way, the tank sinks. If it is lighter than that, then there is a risk of the tank becoming a boat at some point in its life.

Buoyancy Say, "Thank you, Wikipedia!" Have at it . . .

smart ass!

Thanks!

What do you mean by "hold down". Do you mean a neutral buoyancy or a negative buoyancy?

By neutral buoyancy,the tank floats in the water and negative buoyancy, it sinks.

Which ever case you can determine for yourself.

Archimedes' principle states( or paraphrase) that any body would floats in water if the upthrust(buoyancy) is equal to the weight of the body.

Determine these parameters as follows;

1. Determine the weight of the tank i.e the volume of the steel material x the density of steel.

2. Determine the volume of the tank enclosure i.e length x breadth X height.

I believe the tank is empty and sealed or open top and projecting over the water level.

If the tank is completely immersed in the water (as completely covered with water) Multiply the total volume of the enclosure and the density of water to give weight of displaced water that would give a resulting buoyancy.

If the water is not completely covered, find the volume of displaced water = cross sectional area of the base x height of water on the tank side. This gives the resulting buoyancy.

Then check as follows

1. if the resulting buoyancy equals the weight of the tank, therefore the tank would floats

2. if the resulting buoyancy is less than the weight, the tank would sinks.

US volume of tank in gallons X 8.33 lbs - weight of empty tank = neutral buoyancy weight.

or

UK volume of tank in gallons X 10 lbs - weight of empty tank = neutral buoyancy weight.

or

Volume in liters X 1 Kilo - weight of empty tank = neutral buoyancy weight.

In all cases add a bit of weight for negative buoyancy.

Whatever you are covering it with, you will find the weight here: http://www.reade.com/Particle_Briefings/spec_gra2.html

Typical - Gravel, loose, dry = 95 lbs per cubic foot

or Gravel, w/sand, natural = 120 lbs per square foot

Buoyancy is equal to the weight (density X volume) of the displaced water, compared to the weight (density X volume) of the displacing object.

1) Calculate the volume of the displacing object. (your tank, in cubic meters m3)

2) Worst case scenario is that the tank is empty and the water table is higher than the tank so.

3) measure the weight of the empty tank (kg)

4) 1 m3 of water is equal to 1000 kg

5) calculate the the weight (kg) of the displaced volume (m3) of water. and compare to the weight of the empty tank. If the empty tank is less than that, then you must add weight.

6. If you only throw dirt over the thank, then the buoyant forces must only overcome those which it must lift. One way to secure the tank is to place a rigid plate over top of the tank, and then when/if the thank lifts, it must lift ALL the extra weight. When those weights are equal, then there will be no lift, even in the worst case scenario.

Chris