Standard buoyancy calculations refer to atmospheric air pressure. However, the effect of the weight of air underneath the waterline is not included as well as displaced air in tanks, structure and equipment above the waterline. A review of the theoretical mistakes in calculating buoyancy which includes comparison tables of data of different ship types. Suggestions for correcting the apparent mistakes are made. While per mille values for ships are small, per mille buoyancy is a few thousand kN. Documentation of real ships is used for correction of the actual mentioned air weights, thereby yielding precise ship weight and draft values.

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