Flytgräns

Flytgräns, literally “float boundary” in Swedish, is a term used in buoyancy and related fields to describe the boundary between floating and sinking for a body in a fluid. The concept rests on Archimedes’ principle: the buoyant force equals the weight of the displaced fluid. A body will float when its average density is less than or equal to the surrounding fluid’s density, and it will sink if it is denser than the displaced fluid.

In naval architecture and marine engineering, flytgräns is often used to refer to the practical loading or draft limit that allows a vessel to remain afloat under specified conditions. It can denote the maximum displacement or the waterline position (draft) at which safety margins for buoyancy and stability are maintained. Design calculations consider buoyant volume, hull form, ballast, and load distribution to ensure the ship stays above the flytgräns under expected waves and weather.

Smaller-scale applications include flotation devices, buoys, and underwater equipment, where flytgräns defines the threshold between surface flotation and submergence. Various factors influence the boundary in practice, including fluid density, temperature, salinity, hull hydrodynamics, surface tension for very small objects, and dynamic effects from waves and currents.

See also: buoyancy, Archimedes’ principle, density, draft, stability.