Common Buoyancy Calculations

1. Dry weight of an object such as steel, wood, or concrete: Weight = density (lb/ft3) x volume (ft3)

2. Buoyant force (B) is equal to the weight of the water displaced by an object:

3. Submerged weight of object in water equals weight of object in air minum buoyant force:


Positively buoyant: Object rises

Neutral buoyancy: Object floats while submerged

Negatively buoyant: Object sinks

Submerged Weight = dry weight - buoyant force

4. Specific gravity (SG). The density of an object in seawater, in lb/ft3, can be determined by multiplying the specific gravity by 64, or in freshwater by multiplying the specific gravity by 62.4.

5. Irregular shape volume is calculated when the dry weight and density are known: Volume = dry weight (lb)/density (lb/ft3)

B = density of water x volume of the object

o where:

W = dry weight

D = density

V = volume

SG = specific gravity

D^ = density of freshwater

D0 = density of object

B = buoyant force

Wuw = underwater (wet) weight

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