Page 32 - Ship Construction.DJ Eyres 6Ed

Ch03-H8070.fm Page 21 Wednesday, October 18, 2006 6:52 AM
Development of Ship Types 21
hold below. Ro-ro ships may be fitted with various patent ramps for loading
through the shell doors when not trading to regular ports where link span
and other shore side facilities which are designed to suit are available.
Cargo is carried in vehicles and trailers or in unitized form loaded by fork
lift and other trucks. In order to permit the drive through vehicle deck a
restriction is placed on the height of the machinery space and the ro-ro ship
was among the first to popularize the geared medium speed diesel engine
--- ใช้เพื่อการศึกษาเท่านั้น---
with a lesser height than its slow speed counterpart. The dramatic loss of the
ro-ro passenger ships Herald of Free Enterprise in 1987 and Estonia in 1994,
respectively, saw much attention directed at the damage stability of this type of
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
passenger ship when water entered the open un-subdivided deck space.
This has resulted in international regulation requiring, amongst other
things, strengthening and surveillance of bow doors, surveillance of internal
watertight doors used at sea, enhanced damage stability criteria (SOLAS
90) and additional simplified stability information for the master. The Esto-
nia loss led to further stringent damage stability requirements adopted on a
regional basis by northern European countries (Stockholm Agreement
1997). A midship section of a ro-ro passenger/vehicle/train ferry complying
with the requirements of the latter agreement is shown in Figure 17.10.
ึ
HULL FORM Between the 1940’s and 1970 there was a steady increase in
the speed of the dry cargo ship and this was reflected in the hull form of the
vessels. A much finer hull is apparent in modern vessels particularly in
those ships engaged in the longer cargo liner trades. Bulbous bow forms
and open water sterns are used to advantage and considerable flare may be
seen in the bows of container ships to reduce wetness on deck where con-
tainers are stowed. In some early container ships it is thought that this was
probably overdone leading to an undesirable tendency for the main hull to
whip during periods when the bows pitched into head seas. Larger
container ships may have the house three-quarters aft with the full beam
maintained right to the stern to give the largest possible container capacity.

CARGO HANDLING EQUIPMENT Cargo handling equipment, which
remained relatively unchanged for a long period, has received con-
siderable attention since the 1960s. This was primarily brought about by an
awareness of the loss of revenue caused by the long periods of time the
vessel may spend in port discharging and loading cargoes. Conventional
cargo ships are now fitted with steel folding and/or rolling steel hatch covers
of one patent type or another or liftable slab covers of steel, which reduce
maintenance as well as speed cargo handling. Various new lifting devices,
derrick forms and winches have been designed and introduced with marine
shipborne cranes now almost completely replacing rigged derrick installa-
tions on modern ships. These provide further increased rates of loading and
discharge.