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Drydocking of Ships

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Checking of Rudder and Propeller


Newly launched ship using Synchrolift

Dry Docking

"Why is it so quiet?" I woke up asking myself. Not even the generators are running! Very unusual!

Then I realized. My ship was in dry dock. This was the only time when the generators were not running. Even while the ship was at anchorage or alongside the wharf, the noise from the generators was ever present. But not now.

The dry dock is the repair or service yard for the ship. The whole ship is brought to dry land so that the submerged portions of the hull can be cleaned or inspected. This dry docking is done every 12 months to 24 months. Of course, because there will be machinery and systems that cannot stop while the ship is in use, these are also serviced, repaired or replaced at the same time.

Large ships are brought in to a graving dock that consists of a large basin with a gate that can be closed watertight. After the ship is positioned over carefully arranged resting blocks, the water from the basin is pumped out. As the water level drops, the ship gradually rests on the blocks. Wooden wedges are then knocked in to take up any clearances between the hull of the ship and the resting blocks.

In another arrangement, the whole basin can be floated and submerged at will like a submarine. The basin is first submerged and the ship is brought into position as before. Once the ship is in position, the basin is floated up, bring the ship above the water level. This is called a floating dock.

Smaller ships have other arrangements like synchrolift that can lift up the ship like a car in a garage. Once the ship is lifted up, there may be some roller and track arrangements to transport the whole thing to a different place in the shipyard. Slipways are also used when there is enough space. It makes use of a sloping ramp where a small ship resting on a carriage can be pull up using wire ropes.

For a routine dry-docking, the usual work to be done are:

Hull cleaned of marine growth. Painting with anti-corrosive and anti-fouling paints. Sacrificial anodes renewed.
Hull inspection and repairs.
Shipside gratings cleaned and repaired. All overboard and sea suction valves overhauled.
Cleaning and surveying of tanks.
Rudder, carrier ring, pintles, locking devices clearances examined.
Propeller damage, nut looseness, blade polishing done.
Tail shaft bearing wear down checked.
Tail shaft removed and inspected. Coupling bolts and holes deformation.
Anchor chain examined, cleaned and re-marked.
All underwater stuffing boxes repacked.

To the ship's personnel, this is a busy time. Although shipyard workers will do a lot of work, many of the repair and servicing work will be assigned to them. As with everybody working on the ship, this is a time to be extra careful on safety. Many people are working in the same place at the same time.

Some rigging workers are lifting heavy materials using chain blocks, while some machinery workers are dismantling foundation bolts for the engine below. Some welders are cutting pipes just a few feet away. Some workers have removed floor plates so that they can crawl down to inspect the cofferdam. Engine mechanics have dripped lubrication oil on the floor while removing the main bearings. People on the next level are cleaning the boiler tubes, and soot has spilled on the floor.

The whole ship, especially the engine room has become a mess.

For safety purposes, fire hoses connected to shore hydrants are laid on deck and pressurized. Precautions are taken to avoid tools or other materials from falling from the sides of the ship. Safety helmets are a must. Cables or hoses do not obstruct excess to passageways. Fire extinguishers are made available near welding sites. For long stay or cold climates, water in engines or pipes has to be drained away to prevent freezing.

Some of the normal utilities may not be functional at that time. Often, the seamen will have to use the shore shower and toilet facilities. If for any reason cooling seawater is not supplied to the air-conditioning system on board by hoses, then there will not be air-conditioning. Sometimes repair work has to be done on the seawater piping. The boilers have been dismantled, so there is no heating in the living quarters. Sometimes shipping companies arrange special accommodation for their crew on shore during dry-docking.

Dry-docking is not the normal routine work for the seafarer. There may be some time to explore the land too. It could be fun!

2004 Yoon Chee Tuck    Contact me

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