What is the block coefficient (Cb)?

The block coefficient is the ratio of a ship's displaced volume to the volume of the rectangular block formed by its waterline length, beam, and draft. A Cb of 1.0 would be a perfect rectangular barge; a finer hull like a fast yacht might have a Cb of 0.45. It is one of the most fundamental form coefficients in naval architecture.

What is a typical Cb for different vessel types?

Fast naval vessels and sailing yachts: 0.40–0.55. General cargo ships and ferries: 0.60–0.70. Bulk carriers and tankers: 0.75–0.85. Very large crude carriers (VLCCs): 0.82–0.88. Higher Cb generally means more cargo capacity but higher resistance at speed.

What is displaced volume?

Displaced volume (∇, nabla) is the volume of water a vessel displaces when floating at its design waterline. It equals the vessel's displacement mass divided by the water density (1.025 t/m³ for seawater). It can be obtained from hydrostatic curves or stability booklets.

How does Cb relate to ship resistance?

A higher Cb means a fuller, boxier hull that displaces more water per unit length — increasing wave-making resistance at speed. Ships designed to carry maximum cargo at moderate speeds (bulk carriers, tankers) accept a high Cb; fast ships (destroyers, ferries) use a low Cb to reduce resistance.

What is the difference between Cb and Cp (prismatic coefficient)?

Cb is the ratio to the bounding box. Cp (prismatic coefficient) is the ratio of displaced volume to the product of the midship section area and waterline length — it measures how the volume is distributed longitudinally. They are related by Cb = Cp × Cm, where Cm is the midship section coefficient.

Block Coefficient Calculator

Enter displaced volume and hull dimensions to calculate the block coefficient (Cb) of any vessel.

Hull Dimensions

Displaced Volume (∇) (m³)

Waterline Length (LWL) (m)

Molded Beam (B) (m)

Molded Draft (T) (m)

Enter dimensions and click Calculate Cb

Typical Block Coefficients by Vessel Type

Vessel Type	Cb Range
Racing yacht / Fast naval vessel	0.40 – 0.55
Passenger ferry / Container ship	0.55 – 0.68
General cargo / RoRo vessel	0.65 – 0.75
Bulk carrier	0.75 – 0.83
Tanker / VLCC	0.80 – 0.88

Summary

Enter displaced volume and hull dimensions to calculate the block coefficient (Cb) of any vessel.

How it works

Enter the vessel's displaced volume (in cubic meters or cubic feet).
Enter waterline length (LWL), molded beam (B), and molded draft (T).
The calculator computes Cb = ∇ / (LWL × B × T), where ∇ is displaced volume.
The result is displayed with a classification of the hull form type (fine, medium, or full).
Switch between metric (m³, m) and imperial (ft³, ft) units using the toggle.

Use cases

Evaluate the hull form efficiency of a vessel during early design stages.
Compare block coefficients across different ship types to benchmark a new design.
Estimate resistance and powering characteristics from hull form parameters.
Validate displaced volume calculations against known hull dimensions.
Classify a vessel's hull form for preliminary hydrostatic analysis.
Support naval architecture coursework and self-study.

Frequently Asked Questions

Last updated: 2026-09-19 · Reviewed by Nham Vu