Page 30 - Ship Construction.DJ Eyres 6Ed

Ch03-H8070.fm Page 19 Wednesday, October 18, 2006 6:52 AM
Development of Ship Types 19
1970’s many of the cargo liner trades had been taken over by the container
ship and much of the short haul trade undertaken by the conventional dry
cargo ship had passed to the ‘roll-on roll off’ (ro-ro) type of vessel.

CONTAINER SHIPS A feature of the container ship is the stowage of the
rectangular container units within the fuller rectangular portion of the hull
and their arrangement in tiers above the main deck level. In order to facili-
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tate removal and placing of the container units of internationally agreed stan-
dard (ISO) dimensions hold and hatch widths are common. The narrow
deck width outboard of the hatch opening forms the crown of a double shell
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space containing wing ballast tanks and passageways (see Figure 17.9).
Later container ship designs feature hatchless vessels which provide a faster
turnaround in port. These may have hatch covers on the forward holds only,
or none at all, and are provided with substantial stripping pumps for remov-
ing rain and green water from the holds. In recent years the size of con-
tainer ships making oceanic voyages has substantially increased with one
classification society reporting more than 60 vessels of at least 8000 TEU
classed. Although much larger ships can be built, at the time of writing one
of the limiting ship-related factors was the number of tiers of containers
that can be loaded. 10 tiers equating to a load of 356 tonnes on the lowest
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container being that limit. On deck where 60 per cent of the total cargo is
often carried the securing of increasing numbers of containers also presents
a challenge for rough sea navigation and faster port turnarounds. It has
been predicted that vessels capable of 12000 TEU will be built when the
youthful fleet of the turn of the century is due for replacement.

BARGE CARRYING SHIPS Another development in the cargo liner
trade was the introduction of the barge-carrying vessel. An early version of
this type of ship had a particular advantage in maintaining a scheduled ser-
vice between the ports at mouths of large river systems such as between the
Mississippi river in the USA and the Rhine in Europe. Standard unit cargo
barges (sometimes referred to as LASH – lighter aboard ship – barges) are
carried on board ship and placed overboard or lifted onboard at terminal
ports by large deck mounted gantries or elevator platforms in association
with travelling rails. Other designs make provision for floating the barges in
and out of the carrying ship which can be ballasted to accommodate them.
This development appears not to have been as successful as was initially
envisaged in the late 1970’s, and whilst the merits of this type of craft are
still often referred to, the type is now rarely seen.

RO-RO SHIPS These ships are characterized by the stern and in some
cases the bow or side doors giving access to a vehicle deck above the water-
line but below the upper deck. Access within the ship may be provided in
the form of ramps or lifts leading from this vehicle deck to upper decks or