Page 220 - Ship Construction.DJ Eyres 6Ed

Ch19-H8070.fm Page 209 Wednesday, October 18, 2006 6:58 AM

19
Decks, Hatches, and Superstructures

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งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
Decks at different levels in a ship serve various functions; they may be
either watertight decks, strength decks, or simply cargo and passenger accom-
modation decks. Watertight decks are fitted to maintain the integrity of the
main watertight hull, and the most important is the freeboard deck which is
the uppermost deck having permanent means of closing all openings in the
exposed portions of that deck. Although all decks contribute to some extent
to the strength of the ship, the most important is that which forms the upper
flange of the main hull girder, called the ‘strength deck’. Lighter decks
which are not watertight may be fitted to provide platforms for passenger
accommodation and permit more flexible cargo loading arrangements. In
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general cargo ships these lighter decks form tweens which provide spaces in
which goods may be stowed without their being crushed by a large amount
of other cargo stowed above them.
To permit loading and discharging of cargo, openings must be cut in the
decks, and these may be closed by non-watertight or watertight hatches.
Other openings are required for personal access through the decks; and in
way of the machinery space casing openings are provided which allow the
removal of machinery items when necessary, and also provide light and air
to this space. These openings are protected by houses or superstructures,
which are extended to provide accommodation and navigating space. Forward
and aft on the uppermost continuous deck a forecastle and often a poop may
be provided to protect the ends of the ship at sea.

Decks

The weather decks of ships are cambered, the camber being parabolic or
straight. There may be advantages in fitting horizontal decks in some ships,
particularly if containers are carried and regular cross-sections are desired.
Short lengths of internal deck or flats are as a rule horizontal.
Decks are arranged in plate panels with transverse or longitudinal
stiffening, and local stiffening in way of any openings. Longitudinal deck
girders may support the transverse framing, and deep transverses the
longitudinal framing (see Figure 19.1).