very long tanks. The shape of the tanks generally prevents good utilization
of the underdeck space.
SEMI-PRESSURIZED (OR SEMI-REFRIGERATED) TANKS The
capacity of semi-pressurized ships ranges up to about 5000m3 the cargoes
carried being similar to fully-pressurized ships. The independent Type C
tanks are generally constructed of ordinary grades of steel suitable for a
temperature of − 5 °C and are designed for a maximum pressure of about
8kg/cm2. The outer surface of the tank is insulated and refrigeration or
reliquefication plant cools the cargo and maintains the working pressure.
Cargo tanks are often horizontal cylinders mounted on two saddle supports
and many designs (see Figure 23.1) incorporate bio-lobe tanks to better
utilize the underdeck space and improve payload.
FULLY-REFRIGERATED TANKS The capacity of fully-refrigerated ships
ranges from 10 000m3 to 100 000m3 the smaller ships in the range being
multi-product carriers whilst the larger vessels tend to be single product
carriers on a permanent route. Tanks fall almost exclusively into the prismatic,
independent Type A category with tops sloped to reduce free surface
and bottom corners sloped to suit the bilge structure. In most cases they are
subdivided along the centreline by a liquid-tight bulkhead which extends to