Page 39 - Ship Construction.DJ Eyres 6Ed

Ch03-H8070.fm Page 28 Wednesday, October 18, 2006 6:52 AM
28 Ship Construction
of alternative tanker designs, the United States legislation did not, and no
alternative designs were built.
As the result of the break up of the tanker Erika and subsequent pollu-
tion of the French coastline in 1999 IMO members decided to accelerate
the phase out of single hull tankers. As a result in April 2001 a stricter time-
table for the phasing out of single hull tankers entered into force in
September 2003. In December 2003 a decision to further accelerate the
--- ใช้เพื่อการศึกษาเท่านั้น---
phase out dates of single hull tankers was agreed. Pre – MARPOL tankers
being phased out in 2005 and MARPOL tankers and small tankers in 2010
(see Chapter 2 for definitions).
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
Oil tankers now generally have a single pump space aft, adjacent to the
machinery, and specified slop tanks into which tank washings and oily res-
idues are pumped. Tank cleaning may be accomplished by water driven
rotating machines on the smaller tankers but for new crude oil tankers of
20,000 tonnes deadweight and above the tank cleaning system shall use
crude oil washing.

Passenger Ships
ึ
Early passenger ships did not have the tiers of superstructure associated
with modern vessels, and they also had a narrower beam in relation to the
length. The reason for the absence of superstructure decks was the
Merchant Shipping Act 1894 which limited the number of passengers
carried on the upper deck. An amendment to this Act in 1906 removed this
restriction and vessels were then built with several tiers of superstructures.
This produced problems of strength and stability, stability being improved
by an increase in beam. The transmission of stresses to the superstructure
from the main hull girder created much difference of opinion as to the
means of overcoming the problem. Both light structures of a discontinuous
nature, i.e. fitted with expansion joints, and superstructures with heavier
scantlings able to contribute to the strength of the main hull girder were
introduced. Present practice, where the length of the superstructure is
appreciable and has its sides at the ship side, does not require the fitting of
expansion joints.
The introduction of aluminium alloy superstructures provided increased
passenger accommodation on the same draft, and/or a lowering of the light-
weight centre of gravity with improved stability. This was brought about by
the lighter weight of the aluminium alloy structure. Subsequent experience
however has shown that for passenger liners, that are required to maintain
a service speed in a seaway, the maintenance costs of aluminium alloy
superstructures can be higher.
A feature of the general arrangement is the reduction in size of the
machinery space in this time. It is easy to see the reason for this if the