Page 181 - Ship Construction.DJ Eyres 6Ed

Ch16-H8070.fm Page 170 Wednesday, October 18, 2006 6:57 AM
170 Ship Construction
If the double bottom is longitudinally framed in the pounding region, where
the minimum designed draft forward may be less than 4 per cent of the ship’s
length, solid plate floors are fitted at alternate frame spaces, and intercostal
side girders fitted at a maximum spacing of 3 times the transverse floor
spacing. Where the minimum designed draft forward may be more than
4 per cent but less than 4.5 per cent of the ship’s length, solid plate floors may
be fitted at every third frame space and intercostal side girders may have a
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maximum spacing of 4 times the transverse floor spacing. As longitudinals
are stiffening the bottom shell longitudinally, it should be noted that less
side girders need be provided than where the bottom is transversely framed
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
to resist distortion of the bottom with the slamming forces experienced.
Where the ballast draft forward is less than 1 per cent of the ship’s length the
additional strengthening of the pounding region is given special consideration.
Greater slamming forces (i.e. pounding) are experienced when the ship is
in the lighter ballast condition, and is long and slender, by reason of the increased
submersion of the bow in heavy weather with impact also on the bow flare.

BOTTOM STRUCTURE OF BULK CARRIERS Where a ship is classed
for the carriage of heavy, or ore, cargoes longitudinal framing is adopted
for the double bottom. A closer spacing of solid plate floors is required, the
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maximum spacing being 2.5 m, and also additional intercostal side girders
are provided, the spacing not exceeding 3.7 m (see Figure 16.6).
The double bottom will be somewhat deeper than in a conventional
cargo ship, a considerable ballast capacity being required; and often a pipe
tunnel is provided through this space. Inner bottom plating, floors, and
girders all have substantial scantlings as a result of the heavier cargo
weights to be supported.

TESTING DOUBLE BOTTOM COMPARTMENTS Each compartment is
tested on completion with a head of water representing the maximum pressure
head which may be experienced in service, i.e. to the top of the air pipe.
Alternatively air testing is carried out before any protective coatings are
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applied. The air pressure may be raised to 0.21kg/cm , and then lowered to a
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test pressure of 0.14kg/cm . Any suspect joints are then subjected to a soapy
liquid solution test. Water head structural tests will be carried out on tanks
selected by the surveyor in conjunction with the air tests carried out on the
majority of tanks.

Machinery Seats
It has already been indicated that in the machinery spaces additional
transverse floors and longitudinal intercostal side girders are provided to
support the machinery effectively and to ensure rigidity of the structure.