The block coefficient (CB) is a measure of how “full” a ship’s hull form is, calculated by comparing the vessel’s underwater volume to the volume of a rectangular block with the same length, breadth, and draught; a higher CB indicates a fuller, less streamlined hull.
This coefficient directly influences squat— the increase in draught and trim that occurs when a vessel is underway—because fuller-form ships displace more water and generate stronger pressure variations beneath the keel as speed increases, particularly in shallow or restricted waters.
As a result, vessels with high CB values experience more pronounced squat effects than finer-form ships, making them more susceptible to under-keel clearance reductions and requiring more conservative speed management to maintain safe navigation.
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Source: Nautical Academy
