Page 185 - Ship Construction.DJ Eyres 6Ed

Ch17-H8070.fm Page 174 Wednesday, October 18, 2006 6:57 AM

17
Shell Plating and Framing

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The shell plating forms the watertight skin of the ship and at the same time,
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
in merchant ship construction, contributes to the longitudinal strength and
resists vertical shear forces. Internal strengthening of the shell plating may
be both transverse and longitudinal and is designed to prevent collapse of
the plating under the various loads to which it is subject.

Shell Plating

The bottom and side shell plating consists of a series of flat and curved steel
plates generally of greater length than breadth butt welded together. The
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vertical welded joints are referred to as ‘butts’ and the horizontal welded
joints as ‘seams’ (see Figure 17.1). Stiffening members both longitudinal
and transverse are generally welded to the shell by intermittent fillet welds
with a length of continuous weld at the ends of the stiffening member. Con-
tinuous welding of stiffening members to the shell is found in the after peak,
the bottom shell within the forward 30 per cent of the length and where
higher tensile steel is used. Framing is notched in way of welded plate butts
and seams.

BOTTOM SHELL PLATING Throughout the length of the ship the width
and thickness of the keel plate remain constant where a flat plate keel is
fitted. Its thickness is never less than that of the adjoining bottom plating.
Strakes of bottom plating to the bilges have their greatest thickness over
40 per cent of the ship’s length amidships, where the bending stresses are
highest. The bottom plating then tapers to a lesser thickness at the ends of
the ship, apart from increased thickness requirements in way of the pound-
ing region (see Chapter 16).

SIDE SHELL PLATING As with the bottom shell plating the greater
thickness of the side shell plating is maintained within 40 per cent of the
vessel’s midship length and then tapers to the rule thickness at the ends.
The thickness may be increased in regions where high vertical shear stresses
occur, usually in way of transverse bulkheads in a vessel permitted to carry
heavy cargoes with some holds empty. There is also a thickness increase at