THE PROBLEM O F OIL POLLUTION OF THE SEA
223
average by the value of the oil saved (Brummage et al., 1967 ; Brummage, 1968). The 1958 Convention set an upper limit of 100 p.p.m.
oil in water discharged at sea, whereas the last of the slop-tank water
reaches a concentration of 400-1 000 p.p.m. ; but the turbulence of
the wake is such that in the immediately surrounding water this is
reduced to 0.17 p.p.m. IMCO amended the Convention in October
1969, setting a new limit in terms of distance travelled. Sixty litres of
oil per nautical mile will now be permitted which, in trials, produces
no detectable slick. I n some of the latest large tankers (" Universe
Ireland " and " Universe Kuwait ", for example), two wing-tanks
function exclusively as ballast-tanks ; in those which will still require
washing, special coatings and redesigned internal structures reduce
the amount of " clingage " (see Davis, 1968).
It is probable that as many as half a million tons of persistent oils
are nevertheless discharged into the sea each year (Dudley, 1969).
Their source is partly tanker-operators who still do not observe proper
precautions and partly shipping other than tankers. Most generalcargo ships, when sailing only partially loaded, require extra weight
low down in the hull. This is usually provided by filling empty bunkertanks in the double bottom with water which thereby becomes contaminated with fuel oil (in addition to any other pollutants or disease
organisms present in the waters of the port of origin). A typical
freighter carries about 1 000 tons of ballast, which may contain up to
10 tons of oil; in 1964, 16 000 such vessels discharged their ballast
water in U.S. ports alone (U.S. Department of Interior Report, 1967).
Some countries require ships ballasted in this way to carry oil-water
separators but this does not guarantee that they will be used and many
designs are very inefficient (see Shackleton et al., 1960; Permutit Co.
Report, 1966). Many depend on gravity separation, even though the
density of fuel oils is often very near that of the sea in European waters
and may exceed that of tropical or fresh waters (Blade, 1966).
I n any mechanically-powered vessel, particularly oil-fired or motor
ships, the engine-room bilges will also become oily and may exceed
the 100 p.p.m. limit. Ideally, such oily water, as well as recovered oil
from separators, sludge filtered from fuel lines, and other oily wastes
should be discharged to special reception facilities a t the destination
port. I n most European and North American ports these exist and
may even include mobile separator- or tank-barges, but in many others,
facilities are inadequate or lacking (IMCO, 1964). The Faulkner Report
(Ministry of Transport, 1953) points out that 1-2% of the total oil
consumed escapes unburnt through the funnel of an oil-burning ship.
A large vessel on the transatlantic service may burn 6 000 tons in it
223
average by the value of the oil saved (Brummage et al., 1967 ; Brummage, 1968). The 1958 Convention set an upper limit of 100 p.p.m.
oil in water discharged at sea, whereas the last of the slop-tank water
reaches a concentration of 400-1 000 p.p.m. ; but the turbulence of
the wake is such that in the immediately surrounding water this is
reduced to 0.17 p.p.m. IMCO amended the Convention in October
1969, setting a new limit in terms of distance travelled. Sixty litres of
oil per nautical mile will now be permitted which, in trials, produces
no detectable slick. I n some of the latest large tankers (" Universe
Ireland " and " Universe Kuwait ", for example), two wing-tanks
function exclusively as ballast-tanks ; in those which will still require
washing, special coatings and redesigned internal structures reduce
the amount of " clingage " (see Davis, 1968).
It is probable that as many as half a million tons of persistent oils
are nevertheless discharged into the sea each year (Dudley, 1969).
Their source is partly tanker-operators who still do not observe proper
precautions and partly shipping other than tankers. Most generalcargo ships, when sailing only partially loaded, require extra weight
low down in the hull. This is usually provided by filling empty bunkertanks in the double bottom with water which thereby becomes contaminated with fuel oil (in addition to any other pollutants or disease
organisms present in the waters of the port of origin). A typical
freighter carries about 1 000 tons of ballast, which may contain up to
10 tons of oil; in 1964, 16 000 such vessels discharged their ballast
water in U.S. ports alone (U.S. Department of Interior Report, 1967).
Some countries require ships ballasted in this way to carry oil-water
separators but this does not guarantee that they will be used and many
designs are very inefficient (see Shackleton et al., 1960; Permutit Co.
Report, 1966). Many depend on gravity separation, even though the
density of fuel oils is often very near that of the sea in European waters
and may exceed that of tropical or fresh waters (Blade, 1966).
I n any mechanically-powered vessel, particularly oil-fired or motor
ships, the engine-room bilges will also become oily and may exceed
the 100 p.p.m. limit. Ideally, such oily water, as well as recovered oil
from separators, sludge filtered from fuel lines, and other oily wastes
should be discharged to special reception facilities a t the destination
port. I n most European and North American ports these exist and
may even include mobile separator- or tank-barges, but in many others,
facilities are inadequate or lacking (IMCO, 1964). The Faulkner Report
(Ministry of Transport, 1953) points out that 1-2% of the total oil
consumed escapes unburnt through the funnel of an oil-burning ship.
A large vessel on the transatlantic service may burn 6 000 tons in it