Light Ship

The light ship weight (also called lightship displacement or lightweight) is the mass of a vessel when fully equipped and ready for service but without cargo, fuel, ballast, fresh water, stores, crew, or their effects. It represents the fixed structural weight of the hull, machinery, permanently installed equipment, and the fixed outfit. The light ship weight is determined by an inclining experiment conducted by the classification society, usually at the newbuilding stage and repeated if significant structural changes alter the weight. It is the baseline from which deadweight is added to arrive at the full-load displacement. For the chief mate, the light ship weight is a constant that appears in the ship's stability booklet as the starting point for all loading calculations. When calculating the vessel's condition at any point in a voyage, the chief mate enters the light ship KG (height of the centre of gravity above the keel) and then adds the moments contributed by each item of cargo, bunkers, ballast, and fresh water. Any uncertainty in the light ship weight or its centre of gravity coordinates introduces a systematic error in all subsequent stability calculations. Regulatory loading instruments (SOLAS Chapter II-1, Regulation 10) must account for the light ship baseline accurately.