DryDock & Repaires

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.
• Very large ships (tankers, aircraft carriers) are often constructed in graving docks.
• 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.
• Launching from a building berth may be endwise, sidewise, or by in-place flotation.
• 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.