Semisubmerged

Semisubmerged is an adjective used to describe an object that is partly below the surface of a fluid, such as water. In this state, a portion of the object's volume is submerged while another portion remains above the surface.

The concept is rooted in buoyancy. According to Archimedes’ principle, the buoyant force on a floating body equals the weight of the displaced fluid. In static equilibrium, the submerged volume adjusts so that the buoyant force equals the object's weight. The fraction of the volume that is submerged roughly corresponds to the object's density relative to the fluid; a less dense object sits higher, while a denser object sinks deeper.

Contexts and examples vary. In nautical settings, ships and boats typically have most of the hull underwater but with some freeboard above the surface; semisubmerged could describe a vessel in a low-freeboard condition or one taking on water. In offshore engineering, semisubmerged configurations are used for certain floating structures that remain partially submerged, such as semisubmersible platforms that rely on ballast and vertical columns to achieve stability while keeping much of the hull underwater.

Implications of partial submersion include effects on stability, drag, and buoyancy. Extreme semisubmerged states can threaten stability or lead to flooding if ballast and watertight integrity are not properly maintained.

Related terms include buoyancy, draft, freeboard, and semisubmersible platform.