Compute CB directly from volume or estimate a target via Froude & speed.
CB = —
Froude number: —
Suggested target: CB ≈ — (range —)
The block coefficient (CB) is a dimensionless hull-form parameter that describes how full a ship’s underwater volume is relative to a rectangular block defined by its length, beam, and draft. It provides a quick indication of hull fullness and is widely used during early-stage ship design.
CB is defined as the ratio between the displaced underwater volume and the product of the ship’s principal dimensions:
CB = ∇ / (L × B × T)
where ∇ is the submerged volume at draft T, L is the selected length reference (typically Lpp or LWL), and B is the moulded beam.
Typical block coefficient ranges vary by vessel type and operating profile. The following values are indicative and may vary depending on design intent:
CB is commonly used during preliminary ship design to compare hull fullness, assess resistance trends, and verify whether a proposed hull form aligns with expected performance characteristics for its speed range and vessel type.
Lower CB values generally indicate finer hull forms optimized for speed, while higher CB values correspond to fuller hulls optimized for cargo capacity.
The block coefficient is rarely evaluated on its own. The following calculators are commonly used together with CB during preliminary design and performance assessment:
Tip: CB must lie between 0 and 1. Out-of-range values usually indicate inconsistent units, incorrect draft selection, or a mismatch in length reference.