Home > Design Articles > Fluids > Definitions

Prismatic coefficient

This coefficient is calculated by dividing the displacement by the product of the waterline length by the maximum cross sectionnal area. It is represented by the formula Cp=D / (L x Amax)

Block coefficient

This coefficient is calculated by dividing the displacement by the product of the waterline length, the waterline breadth and the hull depth. It is represented by the formula Cb=D / (L x B x T)

Waterplane area coefficient

This coefficient is calculated by dividing the waterplane area by the product of the waterline length and the waterline breadth. The waterplane area is the area enclosed in the waterline on a plan view. It is represented by the formula Cwa=Awp / (L x B)

Transverse and longitudinal GM

This is a measure of the small angle stability of a particular hull form. The higher the GM, the more stable the boat will be at small angles of heel / trim.

Righting arm curve

The righting arm curve shows a plot of righting arm against angle of heel. The righting arm is the amount of righting moment the boat has i.e. how much wind will cause it to heel (lean over) at a given angle. It is from this curve that you can see at which angle capsize will become unavoidable. In the case of the example, this occurs at 133 degrees of heel.