Page 210 - Ship Construction.DJ Eyres 6Ed

Ch18-H8070.fm Page 199 Wednesday, October 18, 2006 6:58 AM
Bulkheads and Pillars 199
Where a doorway is cut in the lower part of a watertight bulkhead care
must be taken to maintain the strength of the bulkhead. The opening is
to be framed and reinforced, if the vertical stiffeners are cut in way of the
opening. If the stiffener spacing is increased to accommodate the opening,
the scantlings of the stiffeners on either side of the opening are increased to
give an equivalent strength to that of an unpierced bulkhead. The actual
opening is kept as small as possible, the access to the shaft tunnel being
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about 1000 to 1250 mm high and about 700 mm wide. In passenger accom-
modation the openings would obviously be somewhat larger.
Mild steel or cast steel watertight doors fitted below the water line are
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either of the vertical or horizontal sliding type. A swinging hinged type of
door could prove impossible to close in the event of flooding and is not
permitted. The sliding door must be capable of operation when the ship is
listed 15°, and be opened or closed from the vicinity of the door as well as
from a position above the bulkhead deck. At this remote control position
an indicator must be provided to show whether the door is open or closed.
Vertical sliding doors may be closed by a vertical screw thread which
is turned by a shaft extending above the bulkhead and fitted with a crank
handle. This screw thread turns in a gunmetal nut attached to the top of the
door, and a crank handle is also provided at the door to allow it to be closed
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from this position. Often horizontal sliding doors are fitted, and these may
have a vertical shaft extending above the bulkhead deck, which may be
operated by hand from above the deck or at the door. This can also be
power driven by an electric motor and worm gear, the vertical shaft working
through bevel wheels, and horizontal screwed shafts turning in bronze nuts
on the door. The horizontal sliding door may also be opened and closed by
a hydraulic ram with a hydraulic hand pump and with control at the door
and above the bulkhead deck (see Figure 18.3). With the larger number of
watertight doors fitted in passenger ships the doors may be closed by means
of hydraulic power actuated by remote control from a central position
above the bulkhead deck.
When in place all watertight doors are given a hose test, but those in a
passenger ship are required to be tested under a head of water extending to
the bulkhead deck. This may be done before the door is fitted in the ship.
In approved positions in the upper tween decks well above the waterline,
hinged watertight doors are permitted. These may be similar to the weather-
tight doors fitted in superstructures, but are to have gunmetal pins in the hinges.

Deep Tanks
Deep tanks were often fitted adjacent to the machinery spaces amidships to
provide ballast capacity, improving the draft with little trim, when the ship
was light. These tanks were frequently used for carrying general cargoes,