A floating marine vessel rests in hydrostatic equilibrium when the upward buoyant force generated by water pressure equals the total downward gravitational weight of the ship. According to Archimedes' principle, the buoyant force equals the weight of the displaced volume of seawater (∇). As the vessel heaves vertically in waves, differential hydrostatic pressure across the submerged hull geometry supplies a linear restoring spring force that drives natural heave oscillation.