Cargo Estimation

Hydrostatic Trim and Water-Density Correction

Adjusting draft-based displacement calculations for bow-to-stern hull trim and port water salinity.

Hydrostatic trim and water-density correction refines draft-based cargo tonnage inference by accounting for hull attitude and port salinity rather than treating a vessel as a flat-bottomed box in uniform seawater. In operational AIS streams, reported drafts frequently reflect stern immersion or dynamic squat while underway, and riverine or estuarine grain ports such as New Orleans or Santos sit in fresh or brackish water well below standard open-ocean density of 1.025 tonnes per cubic meter, causing the same cargo mass to sink deeper. Overwatch applies longitudinal center of flotation polynomials and speed-aware trim inference to adjust aft-biased drafts toward midships, then scales immersed displacement by observed or reference port water density before differencing arrival and departure mass.

Read the cargo validation methodology for validation context.

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