Group Weights in a Ship

The first estimate that the Naval Architect makes for a new ship is to estimate the lightweight.

Lightweight: This is the weight of the ship itself when completely empty, with boilers topped up to working level. It is made up of steel weight, wood and outfit weight, and the machinery weight. This lightweight is evaluated by conducting an inclining experiment normally just prior to delivery of the new vessel. Over the years, this value will change (see Chapter 33).

Deadweight: This is the weight that a ship carries. It can be made up of oil fuel, fresh water, stores, lubricating oil, water ballast, crew and effects, cargo and passengers. This deadweight will vary, depending on how much the ship is loaded between light ballast and fully-loaded departure conditions.

Displacement: This is the weight of the volume of water that the ship displaces:

Hence

Water draft: This is the vertical distance from the waterline down to the keel. If it is to the top of the keel, then it is draft moulded. If it is to the bottom of the keel, then it is draft extreme. Draft moulded is used mainly by Naval Architects. Draft extreme is used mainly by masters, mates, port authorities and dry-dock personnel.

Air draft: This is the quoted vertical distance from the waterline to the highest point on the ship when at zero forward speed. It indicates the ability of a ship to...