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Ship Construction
Bow and Stern
Pounding
and the additional provisions to withstand such pounding:
Heavy pitching assisted by heaving as the
whole vessel is lifted in a seaway may subject the forepart to severe blows
from the sea. The greatest effect is experienced in the light ship condition.
To compensate for this the bottom is strengthened from 0.5L to between 0.25L
and 0.3L from forward depending on the block coefficient, unless the ballast
draught forward is over 0.04L.
Bottom
framed Longitudinally
Longitudinals are to be spaced 1000mm
apart between 0.2L and 0.3L from forward and 700mm apart between 0.2L from
forward and the collision bulkhead. Plate floors are to be fitted alternate
frames, side girders not more than 2.1m apart.
Bottom
framed Transversely
Frame spacing abaft 0.2L from forward is
not to exceed 1000mm and between 0.2L and the collision bulkhead 700mm. Forward of the collision bulkhead 610mm. Plate floors are to
be fitted at every frame. Intercostal side girders are to be not more than 2.2m
apart with half height side girders not more than 1.1m apart, the girders
extending as far as is practicable.
Panting
This is a stress, which occurs at the ends
of a vessel due to variations in water pressure on the shell plating as the
vessel pitches in a seaway. The effect is accentuated at the bow when making
headway.
Panting arrangements are to extend 0.15L
from forward and abaft the after peak bulkhead.
Tiers of beams spaced not more than 2000mm
apart vertically are to be fitted at alternate frames in the fore peak or below
the lower deck above the water line if the forepeak is small. Alternatively
perforated flats may be fitted in lieu of panting beams 2.5m apart vertically.
Tiers of beams are to be supported at the
centreline by a partial wash bulkhead or pillars. Beams are to be bracketed to
frames and the frames to which no beams are attached are to be bracketed to the
stringer. Stringer plates attached to the shell are to be fitted at each tier
of beams.
Abaft the collision bulkhead intercostals
side stringers having the same depth as the frames are to be fitted in line
with those forward of the collision bulkhead and are to extend aft for 0.15L
from the fore end. Stringers may be omitted if the shell plating is of
increased thickness.
Abaft the after peak bulkhead the
structure is to be efficiently stiffened by deep floors and tiers of beams in
association with stringers spaced 2500mm apart vertically.
Stern
Frame
Stern frames may be cast/ forged or
fabricated from steel plate. In the case of cast or forged steel frames they
may be in one piece or in two or more sections riveted or welded together (thermit welding).
Where a riveted connection is used the two
sections of the bar are scarphed together and the
class rules for the scarph are 3D and the depth as
one and one third D, where D is the depth of the bar used in the construction
of the frame.
A scarph fitted
in a rudder post should not be above the highest gudgeon.
Cast steel and fabricated stern frames are
to be strengthened at intervals by transverse webs. All stern frames are to be
efficiently attached to the adjoining structure and the lower part of the stern
frame is to be extended forward to provide an efficient connection to the flat
plate keel.
With larger stern frames there is a
tendency for the whole stern or propeller post and adjacent sections to be
fabricated.