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Description


In dry docking, a ship is removed from the water to enable work to be performed on the exterior part of the ship below the waterline. Ships are constructed on dry docks. In launching, the new or repaired ship is either floated in place or slid from its berth.
  • To prepare the dry dock, keel blocks are set into position and lines and men to handle the vessel are readied. A qualified dockmaster supervises the operation. Dock-based winches are usually used to position the ship in the dock.
  • The most dangerous time in drydocking occurs when support for the ship is changing from water buoyancy to dry dock blocks. If the strength of the blocks is insufficient, they can be crushed, overturning the ship.1
  • Very large ships (tankers, aircraft carriers) are often constructed in graving docks.1
  • Ships are often launched as soon as the hull is completed sufficiently to float safely. They are then moved to an outfitting dock for completion.2
  • Launching from a building berth may be endwise, sidewise, or by in-place flotation.2
  • Launching from a building dock is performed by flooding the dock to the depth required to float the ship.
  • Careful planning and considerable expertise are required to launch a ship by sliding it into the water. Drag chains of predetermined weights are used to control the ship's entry into the water. Tugs are needed to control the ship after entry into the water.3
Equipment
  • Marine Railway - a cradle of wood or steel on rollers. The ship is placed on the cradle and hauled out along a fixed inclined track. This process is usually limited to ships less than 5000 tons.1
  • Floating Dry Dock - a structure with sealed wing walls between which the ship is positioned. Water is pumped out of the wing walls to raise the ship clear of the water line. Water is pumped back into the wing walls to lower the ship back into the water.1
  • Graving Dock - an excavation in the ground that can be flooded when a caisson (i.e., gate) is opened. Once flooded, the ship is floated in, the caisson closed, and the water is pumped out of the excavation.1.
Associated Hazards
  • Injuries, fatalities associated with overturning ship during dry docking and launching operations - catastrophic accidents are unlikely, provided that appropriate procedures are followed.
References

1 Best, A.M. "Dry dock operations." Loss Control Engineering Manual (1975).

2 "Shipbuilding." McGraw-Hill Encyclopedia of Science and Technology (1977).

3 "Shipbuilding." Encyclopedia of Occupational Health and Safety. Geneva: International Labour Organization (ILO), 1983.