On the displacement of ships
2024-06-14
When people talk about ships, they often use the quantifier "ton". For example, "300000 ton large oil tanker", "100000 ton aircraft carrier", "10000 ton large displacement", "thousand ton ocean going fishing vessel", and so on. Upon closer differentiation, it can be found that for ships, the connotations of these "tons" are not exactly the same. Some refer to weight tonnage, while others refer to volumetric tonnage. The "ton" of ships such as "300000 ton ore carriers" and "300000 ton oil tankers" usually refers to the volumetric tonnage, which is the cargo carrying capacity. It is calculated based on the standard of approximately 1 ton per 2.83 cubic meters after measuring and verifying the ship's hull volume. The "ton" of warships such as "100000 ton class aircraft carriers" and "10000 ton large displacement" usually refers to the weight tonnage, which is the weight of the water discharged by the ship in the water - displacement. Empty ships can be divided into self weight and load capacity, so displacement can indicate both the weight of the ship and its carrying capacity. According to the different conditions of the items carried by the ship, the displacement can be divided into empty displacement, standard displacement, normal displacement, full load displacement, and maximum displacement. The unloaded displacement of a warship refers to the displacement when only the weight of the hull, weapons, power equipment, control equipment, and fixed ballast is present, reflecting the lightest loading state that a warship can achieve after construction. Standard displacement refers to the amount of empty displacement plus the weight of personnel, food, fresh water, ammunition, etc., but does not include the displacement of oil and boiler water. On this basis, adding half of the weight of fuel, lubricating oil, and standby boiler water is the normal displacement, which is usually an indicator in ship design and commonly referred to as ship displacement. If the weight of all fuel oil, lubricating oil and standby boiler water is added, it is the full load displacement, which generally reflects the loading condition of the ship when sailing. For example, the displacement of the amphibious assault ship Anadolu of Türkiye Navy is more than 27000 tons, which means the full load displacement. The difference between standard displacement and full load displacement is of great concern. The larger the difference, the more water and oil can be loaded, which can support the ship to sail further. The displacement design of ships is also influenced by other factors, such as the design and construction level of relevant countries and enterprises, limitations of shipyards and port facilities, etc. Therefore, the displacement of ships is usually the result of comprehensive consideration of cost, performance, and task requirements. The maximum displacement, as the name suggests, refers to the displacement of a ship under full load, plus excess fuel, lubricating oil, boiler water, ammunition, as well as excess personnel, food, fresh water, and other weights. The submarine, known as the "water dragon", often floats and dives, so its displacement is divided into water displacement and underwater displacement. The definition of water displacement during submarine ascent is basically the same as that of surface vessels. When a submarine dives, it must fill the ballast tank with water, so its underwater displacement is the normal displacement above water plus the weight of all water in the main ballast tank. In the family of naval vessels, there is a distinction between ships and boats in terms of displacement. Usually, ships with a displacement of over 500 tons are called "ships", while those with a displacement of less than 500 tons are called "boats". However, submarines are a special case, and regardless of their tonnage, they are called "boats". (Lai Xin She)
Edit：Luo yu Responsible editor：Zhou shu
Source：PLA Daily
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