Drydocking is the process of removing a ship entirely from the water into a dry dock — a specially designed basin that can be flooded to float the ship in, then pumped dry — for inspection, maintenance, and repair work impossible to perform while the vessel is waterborne.
Why It’s Mandatory
Classification societies and flag states require vessels to be drydocked at regular intervals (typically within a 5-year cycle, with an intermediate inspection partway through, though exact intervals vary by vessel age and class rules) — this isn’t optional maintenance but a certification requirement to maintain class and flag state seaworthiness certificates.
What Happens During Drydocking
- Hull inspection — full examination of the underwater hull for corrosion, damage, or structural concerns not visible while afloat
- Hull cleaning and repainting — removing marine growth (biofouling) and reapplying antifouling coating
- Propeller, rudder, and thruster inspection and service
- Sea valve and underwater fitting overhaul
- Tank inspections — internal examination of ballast and other tanks
- Thickness measurements — verifying steel plating hasn’t corroded below safe limits
Planning and Cost
Drydocking is a major planned event — vessels are typically off-hire (earning no charter revenue) for the drydock duration, making efficient planning and execution a significant commercial priority alongside the technical requirements.
Exam Relevance
Drydocking requirements, class survey cycles, and typical drydock work scope are standard Ship Knowledge topics in senior deck and engineering officer competency exams.