Coefficients of form

Coefficients used in naval architecture: block coefficient, midship section coefficient, prismatic coefficient and waterplane coefficient.

Block coefficient – The ratio of the underwater volume of a ship to the volume of a rectangular block, the dimensions of which are the length between perpendiculars, the mean draught and the breadth extreme. The relationship is expressed as a decimal figure.

Cb = V/LppBT where V is the volume of displacement, in m3, at draught T.

Coefficient of fineness of a waterplane – The ratio between the area of the waterplane and that of a rectangle of the same length and breadth. The average value of this coefficient for merchant ships is usually between 0.75 and 0.8.

Longitudinal prismatic coefficient – The ratio of the volume of displacement to the volume of a prism with the length equal to the length between perpendiculars and a cross-section area equal to the midship section area.

Midship section coefficient, also coefficient of fineness of the midship section – The ratio between the actual underwater area of a midship section and that of a rectangle of the same depth and width. The average value of this coefficient is 0.9 for merchant ships.

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