Beam-to-draft ratio (B/T)

The beam-to-draft ratio B/T is the molded beam divided by the draft, a form parameter that shapes both stability and resistance. A high B/T (wide and shallow) raises the transverse metacentric radius BM = I_T / V and so the GM, giving a stiff, stable hull but a short, uncomfortable roll period and more wave-making and form drag. A low B/T (narrow and deep) gives a tender, slow-rolling hull with less form resistance. Typical merchant values run about 2.2 to 3.0; barges and shallow-draft river craft go higher. Designers trade B/T against the block coefficient and the length-to-beam ratio to balance stability, seakeeping, powering, and any canal or port draft limit.