Page 211 - Ship Construction.DJ Eyres 6Ed

Ch18-H8070.fm Page 200 Wednesday, October 18, 2006 6:58 AM
200 Ship Construction
and also utilized to carry specialist liquid cargoes. In cargo liners where
the carriage of certain liquid cargoes is common practice it was often an
advantage to have the deep tanks adjacent to the machinery space for cargo
heating purposes. However in modern cargo liners they may require to be
judiciously placed in order to avoid excessive stresses in different con-
ditions of loading. Most ships now have their machinery arranged aft or
three-quarters aft, and are fitted with deep tanks forward to improve the
--- ใช้เพื่อการศึกษาเท่านั้น---
trim in the light conditions.

งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
CONSTRUCTION OF DEEP TANKS Bulkheads which form the bound-
aries of a deep tank differ from hold bulkheads in that they are regularly
subjected to a head of liquid. The conventional hold bulkhead may be
allowed to deflect and tolerate high stresses on the rare occasions when
it has to withstand temporary flooding of a hold, but deep tank bulkheads
which are regularly loaded in this manner are required to have greater
rigidity, and be subject to lower stresses. As a result the plate and stiffener
scantlings will be larger in way of deep tanks, and additional stiffening may
be introduced.
The greater plating thickness of the tank boundary bulkheads increases
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with tank depth, and with increasing stiffener spacing. To provide the greater
rigidity the vertical stiffeners are of heavier scantlings and more closely
spaced. They must be bracketed or welded to some other form of stiffening
member at their ends. Vertical stiffener sizes may be reduced, however, by
fitting horizontal girders which form a continuous line of support on the
bulkheads and ship’s side. These horizontal girders are connected at their
ends by flanged brackets and are supported by tripping brackets at the toes
of the end brackets, and at every third stiffener or frame. Intermediate
frames and stiffeners are effectively connected to the horizontal girders
(see Figure 18.5).
Where deep tanks are intended to carry oil fuel for the ship’s use, or oil
cargoes, there will be a free surface, and it is necessary to fit a centre line
bulkhead where the tanks extend from side to side of the ship. This bulk-
head may be intact or perforated, and where intact the scantlings will be the
same as for boundary bulkheads. If perforated, the area of perforations is
sufficient to reduce liquid pressures, and the bulkhead stiffeners have consider-
ably reduced scantlings, surging being avoided by limiting the perforation area.
Both swedged and corrugated plating can be used to advantage in the
construction of deep tanks since, without the conventional stiffening, tanks
are more easily cleaned. With conventional welded stiffening it may be
convenient to arrange the stiffeners outside the tank so that the boundary
bulkhead has a plain inside for ease of cleaning.
In cargo ships where various liquid cargoes are carried, arrangements
may be made to fit cofferdams between deep tanks. As these tanks may also