Pounding
When a ship meets heavy weather
and commences heaving and pitching, the rise of the fore end of the ship
occasionally synchronizes with the trough of a wave. The fore end then emerges
from the water and re-enters with a tremendous slamming effect, known as
pounding. While this does not occur with great regularity, it may nevertheless
cause damage to the bottom of the ship forward. The shell plating must be
stiffened to prevent buckling. Pounding also occurs aft in way of the cruiser
stern but the effects are not nearly as great.
Panting
As the waves pass along the ship
they cause fluctuations in water pressure which tend to create an in-and-out
movement the shell plating. The effect of this is found to be greatest at the
ends of the ship, particularly at the fore end, where the shell is relatively
flat. Such movements are termed panting and if unrestricted, could eventually
lead to fatigue of the material and must therefore be prevented.
The structure at the ends of the
ship is stiffened to prevent any undue movement of the shell.
Arrangement
to resist Panting & Pounding:
Arrangement to resist panting:
The structure of the ship is
strengthened to resist the effect of panting from 15% of the ships length from
forward to the stem and aft of the after peak bulkhead.
In the forepeak:
o
Side stringers are fitted to the shell at
intervals of 2M below the lowest deck.
o
Channel beams are fitted at alternate frames in
line with the stringers and connected to the frames by brackets. Intermediate
frames are bracketed to the stringer. The free edge of the bulkhead stringer
may be stiffened by one of the beam.
o
The tank top is not carried into the peak, but
solid floors are fitted in each frame. Floor are thicker & flanged on free
edge.
o
The solid frames are 610mm a part and being so
well supported.
o
The deck beams are supported by vertical angle
pillars on alternate frames, which are connected to the panting beams (channel)
and lapped onto the solid floors.
o
A partial
wash plate is usually fitted to reduce the movement of the water in the tank.
o
Inter-coastal plates are fitted for two or three
frame spaces in line with the centre girder.
o
Between the collision bulkhead and 15% length
from the forward, the main frames together with their attachment to the margin,
are increased in strength by 20%. In addition, the spacing of the frames from
the collision bulkhead to 20% of the length from forward must be 700mm.
o
Shell plating thickness is increased by 5% to
15% depending upon ships length.
o
The collision bulkhead is stiffened by vertical
bulb plates spaced about 600mm apart inside the peak.
o
The structure in the aft peak is similar in
principal to that in the fore peak. The stringers and beams may be fitted 2.5m
apart.
Arrangement to resist pounding:
The
structure of the ship is strengthened to resist the effect of pounding
(slamming forces) from collision bulkhead to 25% of the ships length from
forward.
o
The flat bottom shell plating adjacent to the
keel on each side of the ship is increased in thickness between 15% - 25% depending
upon the length.
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The frame spacing in this region is 700 mm
compare with 750mm – 900mm amidships.
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Longitudinal girders are fitted 2.2m apart,
extending vertically from shell to the tank top.
¥
Intermediate half height girders are fitted to
the shell reducing the unsupported width to 1.1M.
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Solid floors are fitted at every frame space and
are attached to the bottom shell by continuous welding.
o
In longitudinally framed ship:
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The spacing of the longitudinal is reduced to
700mm and they are continued as far as forward as to the collision bulkhead.
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Transverse floor may be fitted at alternate
frames.
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Full height side girders may be fitted 2.1m a
part.
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Fore End Structure:
