15 August 2002
Superflooding Feature. For drydock designs including the superflooding
feature, face the drydock seat recesses inboard and outboard to provide bearing
reaction from either direction (refer to Chapter 6).
Alternate Gaskets and Seats. The bearing of caisson ends and keel is
taken through special timber bearing blocks set on both faces of caisson keel and stem.
Rubber gaskets are set into the bearing blocks so that, when not under pressure, the
gaskets project beyond the block faces. Use white oak or greenheart for timber bearing
blocks. When pressure is applied, they compress to form watertight seals. The timber
bearing blocks in this seat design are subject to marine borer attack and decay. This
type of gasket and seat should not be used in locations where marine borer attack of
immersed timber is a problem. See Figure 9-3
Equipment. Mechanical and electrical equipment must conform to the
same specifications as the corresponding equipment in the drydock pumpwell.
Major Equipment. Provide the following major items of equipment. Each
system (caisson tank flooding, caisson tank dewatering, drydock flooding, etc.) must
consist of at least two parallel and independent systems for redundancy:
Vertical shaft pumping units as required. Control by start-stop pushbutton
mounted on or near the floor stand and/or at the control console.
Gate valves of rising stem type or butterfly valves as required for water
control. Use motor operated, except for small valves which may be hand
operated. Provide sea connection with screens and gratings.
Check valves in discharge pipes of main pump units.
Inclinometers of suitable type to show both list and trim.
Gages for indicating the water level in each ballast compartment and draft.
Float type rather than pressure type are necessary in air-operated
caissons due to high air pressure used in blowing out the tanks.
Heating and ventilating systems to suit climatic conditions.
Dock flooding via piping through the caisson and 76.2-mm (30-in) valves
with controls. Two valves are required in each pipe. Use valves suitable
for pressure from both sides to accomodate rotation of the caisson.
Locate pipes high enough to avoid sucking mud and debris on the harbor
bottom into the pipes. Consideration should be given to angling the ends
of pipes down to prevent the movement of ship blocking. Install flanges
on the caisson shell on both sides of the caisson to facilitate the
installation of blanks over the pipes. Refer to Chapter 6.
Electrical Equipment. Supply 460 volts, 3-phase, 60 Hertz per second
electric current from the drydock system to shore connection receptacles on the