Block Coefficient and Waterplane Coefficient ( Cb and Cw)
In this article, we take a look at the definitions and formulae for Block Coefficient and Waterplane Coefficient (Cb and Cw)
Block coefficient (Cb)
Block coefficient (Cb), or coefficient of fineness of displacement, at any draft is the ratio of the underwater volume of the ship at that draft to a rectangular box having the same extreme dimensions.
Formulas : Cb= (Underwater volume) / L x B x d
Underwater volume = L x B x d x Cb
You may also like: MARPOL Annex 4 Certificate: Everything You Need to Know
The term block coefficient may also be used with respect to a tank in which case it would be the ratio of the volume of the tank to the volume of a rectangular box having the same extreme dimensions
as the tank.
Waterplane coefficient (Cw)
Waterplane coefficient (Cw), or coefficient of fineness of the water-plane area, is the ratio of the area of the water-plane to the area of a rectangle having the same length and maximum breadth.
Formulas: Cw = (Area of water-plane)/L x B
Area of water-plane = L x B x Cw
Ref: Ship stability part 1 by Capt. H. Subramaniam