Block Coefficient

The block coefficient Cb is the ratio of a hull’s underwater volume to the volume of the circumscribing box defined by waterline length, beam, and draft: Cb = V / (L x B x T). It indicates fullness of form, running from about 0.55 for fast fine hulls to over 0.85 for slow full-form tankers and bulk carriers. Cb feeds empirical resistance and powering methods such as Holtrop-Mennen, fixes the form factor and wave-making behavior, and appears in the IMO minimum propulsion power guidelines. It is one of the primary non-dimensional coefficients in hull-form definition alongside prismatic and midship-section coefficients.