Ship Displacement Calculator
The ship displacement calculator estimates the total weight of water a vessel displaces when floating freely, which under Archimedes' principle equals the actual weight of the ship.
Understanding Ship Displacement
Unlike ground vehicles, a vessel's weight is measured by how much water it pushes aside when floating. Based on Archimedes' Principle, the buoyant force supporting a floating object equals the exact weight of the fluid displaced by that object. Therefore, a ship that displaces 10,000 tonnes of water weighs exactly 10,000 tonnes.
What is the Block Coefficient ($C_b$)?
A ship's hull is not a perfect rectangular box. The Block Coefficient ($C_b$) represents the ratio between the actual underwater volume of the hull and a conceptual box defined by the Waterline Length (LWL), Beam, and Draft.
- High $C_b$ (0.75 – 0.85): Large cargo carriers, oil tankers, and barges with blunt, boxy hulls designed for storage efficiency rather than speed.
- Medium $C_b$ (0.60 – 0.70): Standard passenger vessels, container ships, and heavy cruisers.
- Low $C_b$ (0.40 – 0.55): High-speed yachts, destroyers, and sailing boats with slender, fine hull lines optimized to slice through water.
Freshwater vs. Saltwater Visual Impact
Ocean water contains dissolved salts, giving it a higher density ($\approx 64 \text{ lbs/ft}^3$ or $1025 \text{ kg/m}^3$) than freshwater ($\approx 62.4 \text{ lbs/ft}^3$ or $1000 \text{ kg/m}^3$). Because marine saltwater is denser, it creates more buoyancy. When a vessel travels from the ocean into an inland fresh river, it will sink slightly deeper into the water (increasing its draft) to displace the extra volume required to match its total static weight.