Dry-Docking: When ships are inspected, cleaned, painted and repaired

All ship owners / managers prefer to reduce the docking time, as costs involved are very high and maintenance sometimes goes into millions of dollars.

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The term ‘Dry-docking’ refers to when a vessel is taken into the dry-dock of a shipyard so that the underwater areas of the hull can be inspected, cleaned, painted, and repaired if required.

Dry-docking is a more broad term, where the entire period of repair, and inspection is termed as “Dry-docking”. In the actual world, ships may be at the Dock for only 4-5 days for the mandatory hull cleaning and painting. The other time (before and after) is spent at the lay berth where other docking-related surveys and maintenance are carried out, which may not be possible to do when the vessel is in service. So the Dry-docking is also a major maintenance period for any vessel. All ship owners/managers prefer to reduce the docking time, as the costs involved are very high and maintenance sometimes goes into millions of dollars.

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Regulatory requirement:

SOLAS regulations, set out by the International Maritime Organisation (IMO), require all merchant ships to undergo an intermediate survey within 36 months and a comprehensive inspection of the hull in a dry dock twice within a five-year period. This survey is often referred to as “Docking survey”. Docking includes mandatory inspection and maintenance of the hull, propeller, rudder, etc., and other parts which are always immersed in water and are generally inaccessible by the ship’s crew when the ship is in service.
Before the age of 15 years, the actual docking can take place every 5 years +- 6 months, with the intermediate one being relaxed to an IWS (In-water survey), where specialist divers inspect the hull and clean if required, to the satisfaction of the vessel’s Classification society.

Phases of Dry-Docking:

Phase 1: Preparation.

This involves thorough planning. In this stage, every aspect of the dry-docking procedure is carefully planned. Dry dock specs are prepared by the vessel and sent across to the vessel manager. The vessel managers discuss the plan with owners and certain jobs are added/removed from the final list. The list of jobs is provided to the shipyard and quotations are obtained. Lots of to-and-fro emails between the office and shipyard. Finally, the Shipyard is booked. Some non-mandatory jobs may be deleted, depending on the budget of the ship owner.

Phase 2: Arrival at the shipyard.

The vessel arrives at the shipyard empty (only with Ballast water) and is safely docked at a lay berth/anchorage. Jobs are identified by the Shipyard and discussed with the crew. Daily meetings ensure this

Phase 3: Docking of the vessel.

This is a critical phase and I will not get into the technical details. Before docking, the stability of the vessel is worked out by the Master & Chief officer and exchanged with the Dock Master. Once agreed, the Dock Master then sets the wooden/concrete blocks for the vessel at the Dock, as per the Docking plan of the vessel which was provided earlier. The vessel needs to have minimum Ballast on board with a desirable trim by the stern. Usually at this stage, the ship's engines are not operational and all movements are done by Tug boats. On the day, the vessel is towed into the Dry Dock and positioned by using various tugs. Once in line, the gates are closed and water is pumped out. Gradually the vessel sits on the blocks. In between, Divers go down to check the positioning of the vessel with respect to the blocks placed before. Once the vessel is fully on the blocks, the bottom plugs are opened by the shipyard and the balance Ballast water is left to drain by gravity. If possible, the vessel's ballast pumps are also used to assist in quickly emtying the Ballast tanks. At a Dry-Dock, most of the vessel's machinery is in-operational, and shore power is provided by the shipyard.

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Phase 4: Maintenance and Repair.

Though the maintenance and repair happen at all stages and on a daily basis, here we are referring to the maintenance for the Hull which cannot happen when the ship is afloat. The Hull is inspected by the Class inspector and others. The maintenance plan is discussed and the Hull maintenance starts, which ends with a painting of the Hull with “Anti-Fouling” Paint. Various other openings, Rudder, Propeller, etc. are also inspected and maintenance carried out.

Phase 5: Undocking.

This is another critical part of dry-docking. The watertight integrity of the plugs removed before and of various openings is checked using a vacuum test. Just one day before undocking, the Chief officer takes in the same amount of Ballast water, just like how it was before. Since the vessel’s pumps are usually in-operational, the water is provided by the shipyard using fire hoses. On the day, the shipyard pumps water in the dock and slowly the vessel starts floating. Once afloat, the dock gate is opened and the vessel is towed to a lay berth, to complete the balance maintenance jobs.

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Phase 6: Testing Trials, and Departure from shipyard.

During this stage, various machinery which have been opened up for maintenance are to be tried out satisfactorily, some in the presence of a Class surveyor. If major jobs are done on the Main Engine, then sea trials may also be done. Once all machinery is tried out and all certification completed, the vessel is allowed to sail out from the shipyard, thus completing its docking period and going back into trading service.

I have just provided a brief introduction to the docking of ships. All technical details are excluded, as the article would then become boring. Now let the photos and videos do the talking.

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Note: All photgraphs and videos are taken by the Author. No permission, either express or implied, is granted for the electronic transmission, storage, retrieval, transfering or printing of the photographs.-

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