Fouling grows quietly and costs fuel. Hull cleaning is the removal of marine growth—slime, weeds, and shell—from the underwater surface of a ship’s hull to restore hydrodynamic performance.

Cleaning may be done by divers with brushes or by remotely operated vehicles, either in water or during drydock. Soft growth can be removed gently; hard growth may require more aggressive methods that risk damaging coatings. Many ports restrict in-water cleaning to limit the spread of invasive species.

Operators schedule cleaning when speed-loss data show that the fuel penalty exceeds the cost of the operation. Proactive cleaning and good antifouling coatings reduce the frequency of heavy interventions. A clean hull is one of the most direct ways to cut fuel consumption on an existing ship.

• Removal of marine growth from the underwater hull
• Done by divers or underwater robots
• Restores speed and reduces fuel use
• Subject to environmental restrictions in many ports