Page 40 - Ship Construction.DJ Eyres 6Ed

Ch03-H8070.fm Page 29 Wednesday, October 18, 2006 6:52 AM
Development of Ship Types 29
Aquitania, built in 1914 and having direct drive turbines with twenty-one
double–ended scotch boilers, is compared with the Queen Elizabeth 2. The
latter as originally built had geared drive turbines with three water tube
boilers. Many modern passenger ships have had their machinery placed aft;
this gives over the best part of the vessel amidships entirely to passenger
accommodation. Against this advantage, however, allowance must be made
for an increased bending moment if a suitable trim is to be obtained. The
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more recent provision of electric podded propulsors as fitted on the Queen
Mary 2 has, with the removal of shaft lines, permitted optimisation of the
internal arrangements of the passenger liner and cruise ship.
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Passenger accommodation standards have increased substantially, the
volume of space allotted per passenger rising steadily. Tween deck clear-
ances are greater and public rooms extend through two or more decks,
whilst enclosed promenade and atrium spaces are now common in these
vessels. The provision of air conditioning and stabilizing devices have also
added to passenger comfort. Particular attention has been paid to fire
safety in the modern passenger ship, structural materials of low fire risk being
utilised in association with automatic extinquishing and detection systems.
There has been a demise of the larger passenger liner and larger passenger
ships are now either cruise ships, short haul ferries or special trade passenger
ึ
(STP) ships. The latter being unberthed immigrant or pilgrim passenger
ships operating in the Middle East to South East Asian region.
Whilst the safety of passenger ships in general has been good in recent
years the growth in the size and number of cruise ships has led IMO to ini-
tiate a review of passenger ship safety. In particular it is looking at placing
greater emphasis on the prevention of a casualty from occurring in the first
place. That is future passenger ships should be designed for improved sur-
vivability so that in the event of a casualty passengers and crew can stay
safely on board as the ship proceeds to port.
The development of high speed passenger ferries of lightweight con-
struction and often of radical hull form and/or non-displacement modes of
operation has been notable since the early 1980’s. Initially relatively small,
these craft may now be more than 100 metres in length and carry upwards
of 500 persons plus 100 cars/30 trucks or more. The lightweight con-
struction is usually of aluminium alloy but some have been constructed of
lighter higher tensile steels and fibre reinforced plastics may be used in the
superstructure and accommodation areas. With speeds of up to 50 knots
many craft are of twin-hull form and include conventional catamarans,
wave piercers with twin hulls and a faired buoyant bridging structure
forward, also small waterplane twin hulled (SWATH) ships. The latter
have a high proportion of their twin-hull buoyancy below the waterline
(see Figure 3.7). Other high speed craft include hydrofoils, and various sur-
face effect ships (SESs) including hovercraft which maintain a cushion of
air, fully or partially, between the hull and the water to reduce drag. The