Page 204 - Ship Construction.DJ Eyres 6Ed

Ch18-H8070.fm Page 193 Wednesday, October 18, 2006 6:58 AM
Bulkheads and Pillars 193
structural compensation is introduced. In container ships the spacing is
arranged to suit the standard length of containers carried.
Each of the main watertight hold bulkheads may extend to the upper-
most continuous deck; but in the case where the freeboard is measured
from the second deck they need only be taken to that deck. The collision
bulkhead extends to the uppermost continuous deck and the aft peak
bulkhead may terminate at the first deck above the load waterline pro-
--- ใช้เพื่อการศึกษาเท่านั้น---
vided this is made watertight to the stern, or to a watertight transom floor.
In the case of bulk carriers a further consideration may come into the
spacing of the watertight bulkheads where a shipowner desires to obtain a
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
reduced freeboard. It is possible with bulk carriers to obtain a reduced free-
board under The International Load Line Convention 1966 (see Chapter
31) if it is possible to flood one or more compartments without loss of the
vessel. For obvious reasons many shipowners will wish to obtain the maxi-
mum permissible draft for this type of vessel and the bulkhead spacing will
be critical. Additionally SOLAS amendments now require that bulk carriers
constructed after 1 July 1999 and of 150 metres or more in length of single
side skin construction and designed to carry solid bulk cargoes of
1000 kg/cubic metre or more when loaded to the summer load line must be
able to withstand flooding of any one cargo hold.
ึ
SPACING OF WATERTIGHT BULKHEADS – PASSENGER SHIPS Where
a vessel requires a passenger certificate (carrying more than 12 passengers),
it is necessary for that vessel to comply with the requirements of the Inter-
national Convention on Safety of Life at Sea, 1974 (see Chapter 29). Under
this convention the subdivision of the passenger ship is strictly specified,
and controlled by the authorities of the maritime countries who are signato-
ries to the convention. In the United Kingdom the controlling authority is the
Marine and Coastguard Agency.

CONSTRUCTION OF WATERTIGHT BULKHEADS The plating of a
flat transverse bulkhead is generally welded in horizontal strakes, and
convenient two-dimensional units for prefabrication are formed. Smaller
bulkheads may be erected as a single unit; larger bulkheads are in two or
more units. It has always been the practice to use horizontal strakes of
plating since the plate thickness increases with depth below the top of the
bulkhead. The reason for this is that the plate thickness is directly related to
the pressure exerted by the head of water when a compartment on one side
of the bulkhead is flooded. Apart from the depth the plate thickness is also
influenced by the supporting stiffener spacing.
Vertical stiffeners are fitted to the transverse watertight bulkheads of
a ship, the span being less in this direction and the stiffener therefore
having less tendency to deflect under load. Stiffening is usually in the form
of welded inverted ordinary angle bars, or offset bulb plates, the size of the