Page 237 - Ship Construction.DJ Eyres 6Ed

Ch20-H8070.fm Page 226 Wednesday, October 18, 2006 6:59 AM

20
Fore End Structure

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Consideration is given in this chapter to the structure forward of the
collision bulkhead. The chain locker is included as it is usually fitted
forward of the collision bulkhead below the second deck or upper deck, or
in the forecastle itself. An overall view of the fore end structure is shown in
Figure 20.1, and it can be seen that the panting stiffening arrangements are
of particular importance. These have already been dealt with in detail in
Chapter 17 as they are closely associated with the shell plating.
On the forecastle deck the heavy windlass seating is securely fastened,
and given considerable support. The deck plating thickness is increased
locally, and smaller pillars with heavier beams and local fore and aft inter-
costals, or a centre line pillar bulkhead, may be fitted below the windlass.
ึ

Stem งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี

On many conventional ships a stem bar, which is a solid round bar, is fitted
from the keel to the waterline region, and a radiused plate is fitted above
the waterline to form the upper part of the stem. This forms what is referred
to as a ‘soft nose’ stem, which in the event of a collision will buckle under
load, keeping the impact damage to a minimum. Older ships had solid bar
stems which were riveted and of square section, and as the stem had no
rake it could cause considerable damage on impact because of its rigidity.
Small ships such as tugs and trawlers may still have a solid stem bar extend-
ing to the top of the bow, and some existing large passenger ships may have
steel castings or forgings forming the lower part of the stem. A specially
designed bow is required for ships assigned ‘icebreaker’ notation and addi-
tional scantlings are required for the stems of ships assigned other ice
classes (see Chapter 17).
The solid round bar is welded inside the keel plate at its lower end, and
inside the radiused stem plate at its upper end, the shell being welded each
side (Figure 20.1). It is necessary to support that part of the stem which
is formed by radiused plates with ‘breast hooks’, i.e. horizontal plate webs,
between the decks and below the lowest deck, in order to reduce the unsup-
ported span of the stem. Where the plate radius is large, further stiffening is
provided by a vertical stiffener on the centre line. The thickness of these