Page 271 - Ship Construction.DJ Eyres 6Ed

Ch22-H8070.fm Page 260 Wednesday, October 18, 2006 6:59 AM
260 Ship Construction
transverses have a maximum spacing of between 2.5 m and 3.5 m depending
on length of ship, and are connected to transverses arranged under the decks
in line with the side transverses. Forecastles have web frames to support any
longitudinal side framing, and the forecastle deck may be supported by
pillars at its centre line.

ICE STRENGTHENING With the growing export of oil from Russia an
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increasing number of new tankers are being provided with ice strengthen-
ing forward (see Chapter 17) so that they can trade to parts of the Baltic
Sea that can be frozen in winter. These include several 20,000 tonne dead-
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weight ice breaking oil tankers.

After End Structure

The machinery is arranged aft in ocean-going tankers, and a transversely
framed double bottom structure is adopted in way of the machinery space.
Constructional details of this double bottom are similar to those of the con-
ventional dry cargo ship with floors at each frame space, additional side
girders, and the engine seating integral with the bottom stiffening members.
ึ
Transverse or longitudinal side and deck framing may be adopted in
way of the engine room and aft of this space. If transversely framed, web
frames are fitted not more than five frame spaces apart below the lowest
deck and may be supported by side stringers. The web frames may be
extended into the poop; and where an all-houses aft arrangement is
adopted they may also extend into the superstructure. Similar transverse
webs are introduced to support any longitudinal framing adopted in a
machinery space. Transverse webs have the same spacing as web frames
except in tween decks above the aft peak where the maximum spacing is
four frame spaces.
The aft peak and stern construction follows that of other merchant ship
types, a centre line bulkhead being provided in the aft peak. Any ice
strengthening is similar to that required in other ships (see Chapter 17).

Superstructures

To permit the assignment of deeper freeboards for oil tankers, the condi-
tions of assignment of load line (see Chapter 31) stipulate the requirements
for protective housings enclosing openings in the freeboard and other decks.
They also require provision of a forecastle covering 7 per cent of the ship’s
length forward.
Structurally the houses are similar to those of other vessels, special atten-
tion being paid to the discontinuities in way of breaks at the ends of the