TANKER CAE0O ' *
attings at the exhaust end of the coils as installed by Messrs. T. B.
Bilton & Sons, North Shields.
The trunkway increases the stability of the vessel by reducing the
surface area of the oil All liquid cargoes are unstable if the tanks are
not completely filled and this cannot be done in tankers, so when the
ship rolls at sea the free liquid shifts from side to side and if the quantity
were excessive the ship would be liable to capsize. The middle liiie
bulkhead being carried to the top of the trunk divides it so that the
volume of free oil is comparatively small and ineffective.
The side tanks may be used for oil, dry cargo or bunkers, if required
to put the ship down to her load line. When loading light spirit in the
summer season the main tanks are not in themselves usually of sufficient
capacity to put the ship down to her summer mark and the summer
tanks are then utilised. The specific gravity of oil vanes with its
temperature from about *98 in the case of heavy oils to about *85 for
petroleum.
Tube ventilators capable of being opened and closed are fitted to the
tanks to admit air, or to allow the gas to escape, and they may be
legulated to prevent undue evaporation from spirit cargoes, otherwise
there would be considerable loss in quantity. The air pipes may be
led from the tanks to a considerable height, sometimes up the masts,
to carry vapour well clear of the ship when loading or discharging
highly inflammable spirit, the tanks being, of course, kept closed during
the operation.
When the cargo is pumped out every precaution must be taken to
ensure that the empty tanks are gas free, the ship being provided
with suction fans to draw off heavy gases up through piping, or with
steam injectors which create a vertical current and serve the same
purpose.
Oil cargoes are pumped in and out through flexible metallic hose
either by pumps on board or on shore. The pumping and piping
system forms a most important part of a tanker's outfit, the plant
installed in modern ships being capable of pumping up to 500 tons of
oil per hour.
Two main, pipe lines are usually led from the several pump rooms
with "branch lines connecting up to each tank and fitted with control
valves, so that the tanks may be worked iiwjependently or in groups,
or oil may be passed from one tank to another by simply manipulating
the proper valves. Needless to say, one oi the first duties on joining
a tanker is to study closely her pumping plan, and to understand and be