T H E PROBLEM O F OIL POLLUTION O F THE SEA
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11. SOURCES AND CONTROL
A. Tanker operation and general-cargo shipping
The largest and most dramatic spillages of oil at sea have resulted
from the collision or stranding of tankers. It has been argued that the
current trend towards very large bulk carriers should reduce this risk,
because fewer voyages are necessary to keep any one refinery or tankfarm supplied. Nevertheless, in the three years ending with April 1967,
91 tankers went aground and 238 were involved in collision. 19% of
the groundings and 9% of the collisions resulted in cargo spillage-a
total of 39 incidents. I n the first five months of 1968, a further 39
tankers were involved in various accidents, not all resulting in oil-spills
(Brockis, 1967; Select Committee, 1968). When a large tanker is
damaged, it is obvious that she is potentially capable of losing a great
deal of oil ; modern design trends do little to minimize this possibility.
Before the 1939-45 war, typical tankers carried 10 000-12 500 tons of
cargo at speeds up to 12 knots. To meet wartime demands, American
shipyards went into mass-production of the T2 tanker, carrying some
16 500 tons at a sustained speed of 144 knots. For some years after
the war, this type formed the backbone of tanker fleets before it was
ousted by " supertankers " (as they were called in the early 1950s) of
about 24 000 tons.
Tankers are constructed on a basic plan of three longitudinal series
of tanks ; in the T2 and related designs, these were about 36 ft long.
After the closure of the Suez Canal in 1956, even larger and faster
tankers became economically desirable ; the implications of their
deviation from earlier designs are reviewed in the Batelle-Northwest
Report (1967). To reduce hull weight and simplify the plumbing,
alternate wing-tank divisions became swash bulkheads (incomplete
divisions which merely reduce cargo movement) ; in later designs this
practice was extended to the centre tanks. Many recently-built vessels
of 40 000-60 000 tons have tanks which are effectively 80-100 ft long.
A greater capacity (and larger tanks) can be incorporated in older
tankers by the process of " jumboizing ", in which a new and larger
centre-section is inserted between the original bows and stern, which
contain expensive machinery, crew-quarters, etc. Many T2 tankers
were enlarged in this way, although the best-known example is now
( ( Torrey Canyon ", which " grew " from 67 000 to 118 000 tons. The
capacity of today's '( supertankers "in the 100 000-500 000 tons range
is obtained by increasing draught and breadth rather than length, so
that a tank only three times as long as those in the T2 design may contain fifty times as much oil-the entire cargo of a pre-war tanker. Some
219
11. SOURCES AND CONTROL
A. Tanker operation and general-cargo shipping
The largest and most dramatic spillages of oil at sea have resulted
from the collision or stranding of tankers. It has been argued that the
current trend towards very large bulk carriers should reduce this risk,
because fewer voyages are necessary to keep any one refinery or tankfarm supplied. Nevertheless, in the three years ending with April 1967,
91 tankers went aground and 238 were involved in collision. 19% of
the groundings and 9% of the collisions resulted in cargo spillage-a
total of 39 incidents. I n the first five months of 1968, a further 39
tankers were involved in various accidents, not all resulting in oil-spills
(Brockis, 1967; Select Committee, 1968). When a large tanker is
damaged, it is obvious that she is potentially capable of losing a great
deal of oil ; modern design trends do little to minimize this possibility.
Before the 1939-45 war, typical tankers carried 10 000-12 500 tons of
cargo at speeds up to 12 knots. To meet wartime demands, American
shipyards went into mass-production of the T2 tanker, carrying some
16 500 tons at a sustained speed of 144 knots. For some years after
the war, this type formed the backbone of tanker fleets before it was
ousted by " supertankers " (as they were called in the early 1950s) of
about 24 000 tons.
Tankers are constructed on a basic plan of three longitudinal series
of tanks ; in the T2 and related designs, these were about 36 ft long.
After the closure of the Suez Canal in 1956, even larger and faster
tankers became economically desirable ; the implications of their
deviation from earlier designs are reviewed in the Batelle-Northwest
Report (1967). To reduce hull weight and simplify the plumbing,
alternate wing-tank divisions became swash bulkheads (incomplete
divisions which merely reduce cargo movement) ; in later designs this
practice was extended to the centre tanks. Many recently-built vessels
of 40 000-60 000 tons have tanks which are effectively 80-100 ft long.
A greater capacity (and larger tanks) can be incorporated in older
tankers by the process of " jumboizing ", in which a new and larger
centre-section is inserted between the original bows and stern, which
contain expensive machinery, crew-quarters, etc. Many T2 tankers
were enlarged in this way, although the best-known example is now
( ( Torrey Canyon ", which " grew " from 67 000 to 118 000 tons. The
capacity of today's '( supertankers "in the 100 000-500 000 tons range
is obtained by increasing draught and breadth rather than length, so
that a tank only three times as long as those in the T2 design may contain fifty times as much oil-the entire cargo of a pre-war tanker. Some