Dry Dock
A Dry Dock is a basin that can be flooded to allow a vessel to enter, then drained so the vessel rests on supports with its hull fully exposed for inspection, repair, painting, propeller work, sea-chest cleaning, and other underwater maintenance. Dry-docking is fundamental to ship maintenance — most class societies require ships to be dry-docked twice every 5 years.
Dry docks come in several types: graving docks (excavated into the shoreline with a sealing gate), floating docks (submersible barges that lift the vessel), and marine railways (slipways with cradles). Major shipyards operate multiple dry docks of varying sizes — some accommodating ULCC tankers and aircraft carriers.
The dry-docking workflow is complex: pre-arrival inspection, docking plan, scaffolding, hull blast and paint, propeller and rudder work, anode replacement, sea valve overhauls, defects from PMS, class survey items, owner's additional works, undocking, and sea trials. All managed against a tight schedule and budget.
Dry-docking is the most expensive and complex event in a ship's operating life, and class requires it twice every five years. Every day in dock is off-hire and cost, so tight control of scope, schedule and budget is what decides whether a docking stays within the maintenance plan or blows through it.
hull exposed
props · anodes
& repairs
& sea trial
How often must a ship be dry-docked?
Most class regimes require two dockings within any five-year period, with a maximum interval between them — though some ships qualify for extended in-water survey arrangements.
What is the difference between a graving dock and a floating dock?
A graving dock is excavated into the shoreline and sealed with a gate, then drained. A floating dock is a submersible structure that sinks to let the ship in, then rises to lift it clear of the water.