Page 205 - Ship Construction.DJ Eyres 6Ed

Ch18-H8070.fm Page 194 Wednesday, October 18, 2006 6:58 AM
194 Ship Construction
stiffener being dependent on the unsupported length, stiffener spacing,
and rigidity of the end connections. Rigidity of the end connections will
depend on the form of end connection, stiffeners in holds being bracketed
or simply directly welded to the tank top or underside of deck, whilst upper
tween stiffeners need not have any connection at all (see Figure 18.1).
Vertical stiffeners may be supported by horizontal stringers permitting a
reduction in the stiffener scantling as a result of the reduced span. Horizon-
--- ใช้เพื่อการศึกษาเท่านั้น---
tal stringers are mostly found on those bulkheads forming the boundaries of a
tank space, and in this context are dealt with later.
It is not uncommon to find in present day ships swedged and corrugated
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
bulkheads, the swedges like the troughs of a corrugated bulkhead being so
designed and spaced as to provide sufficient rigidity to the plate bulkhead
in order that conventional stiffeners may be dispensed with (see Figure 18.2).
Both swedges and corrugations are arranged in the vertical direction like
the stiffeners on transverse and short longitudinal pillar bulkheads. Since
the plating is swedged or corrugated prior to its fabrication, the bulkhead
will be plated vertically with a uniform thickness equivalent to that required
at the base of the bulkhead. This implies that the actual plating will be
somewhat heavier than that for a conventional bulkhead, and this will to a
large extent offset any saving in weight gained by not fitting stiffeners.
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At the lower end of transverse hold bulkheads in bulk carriers a bulkhead
stool is generally fitted (see Figure 18.3) at the lower end of the bulkhead.
This provides a shedder surface for cargo removal rather than a tight corner
at the bulkhead/tank top interface. Inclined shedder plates or gussets are
also fitted between the corrugations directly above the stool. The addition
of a vertical plate bracket under the inclined shedder plate at mid – point of the
corrugation stiffens and supports the corrugation against collapse under load.
The boundaries of the bulkhead are double continuously fillet welded
directly to the shell, decks, and tank top.
A bulkhead may be erected in the vertical position prior to the fitting of
decks during prefabrication on the berth or assembly into a building block.
At the line of the tween decks a ‘shelf plate’ is fitted to the bulkhead and
when erected the tween decks land on this plate which extends 300 to
400 mm from the bulkhead. The deck is lap welded to the shelf plate with
an overlap of about 25 mm. In the case of a corrugated bulkhead it becomes
necessary to fit filling pieces between the troughs in way of the shelf plate.
If possible the passage of piping and ventilation trunks through watertight
bulkheads is avoided. However in a number of cases this is impossible and to
maintain the integrity of the bulkhead the pipe is flanged at the bulkhead.
Where a ventilation trunk passes through, a watertight shutter is provided.

TESTING WATERTIGHT BULKHEADS Both the collision bulkhead,
as the fore peak bulkhead, and the aft peak bulkhead provided they do
not form the boundaries of tanks are to be tested by filling the peaks with