Displacement Tonnage

Displacement is the mass of water the hull pushes aside, equal by Archimedes’ principle to the vessel’s own mass at that draft. In seawater of 1.025 t/m3, displacement (t) is the underwater volume (m3) times 1.025. Lightship displacement is the empty vessel; loaded displacement at the summer mark less lightship gives deadweight. Naval ships are sized by displacement rather than deadweight, since their payload is weapons and systems, not revenue cargo.