Buoyancy

Buoyancy is the upward force produced by the pressure distribution around a body in a fluid. In still water, pressure is higher at greater depth, so the vertical pressure components do not cancel. The resulting force acts through the center of buoyancy, which is the centroid of the displaced fluid volume.

For a floating vessel in static equilibrium, the buoyant force equals the vessel weight:

where \rho is fluid density, g is gravitational acceleration, and \nabla is displaced volume. This relationship is simple, but it carries much of naval architecture: loading, ballast, draft, reserve buoyancy, damaged stability, and floating-platform design all depend on the displaced volume and its position.

Engineering use

Buoyancy is used to estimate whether a body floats, how deep it sits, how much load it can carry, and how it responds when it heels, trims, floods, or changes density environment. It applies to ships, offshore platforms, pontoons, submarines, buoys, docks, tanks, remotely operated vehicles, and submerged equipment.

In stability analysis, the magnitude of buoyancy must be paired with its line of action. When a vessel heels, the underwater shape changes and the center of buoyancy shifts. That shift creates a righting arm if the geometry and center of gravity are favorable.

Common mistakes

A common mistake is treating buoyancy as a fixed upward force independent of loading condition. Buoyancy changes with displaced volume and fluid density. Another mistake is using buoyant force alone to judge safety; a vessel can float and still have inadequate stability, insufficient freeboard, poor damaged survivability, or unacceptable motion in waves. A strong buoyancy review states displacement, water density, loading condition, draft, trim, center of gravity, and stability assumptions.