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.
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