238
A. NELSON-SMITH
allowance should be given for strong ocean or tidal currents. Calculations made when plotting the drift of " Torrey Canyon " oil showed it
to move in the direction of the wind at about 3.4% of its speed (Smith,
1968). This agrees well with measurements of surface drift in the
Atlantic made by Hughes ( I 956), using floating plastic envelopes which
travelled with the wind at 3.3% of its velocity. An oil-slick released
experimentally in Japanese waters travelled at 4% wind speed (reported by Brockis following Berridge et al., 1968a) while the German
Hydrographic Institute, plotting the movement of oil from the " Gerd
Maersk " after her accident in the North Sea in 1955, showed that it
moved a t about 4.2% wind speed (Tomczak, 1964). Earlier experiments
at sea off the United States in 1926-27 and off the British Isles in 1952
are referred to in the Faulkner Report (Ministry of Transport, 1953).
Slicks were followed for 90 miles over 72 h during the American experiment, when it was concluded that most persistent oils will form an
invisible film and thus " disappear " within 100 h of discharge; the
British experimenters tracked a slick for 20 miles over eight days.
Evidence from the Department of the Government Chemist, appended
to the Report, suggests that even very thin films can build up on a
windward shore to cause appreciable pollution. Berridge et nl. (1968b)
report that emulsions containing less than 50% water appear, on
casual inspection, to be undiluted oil. These emulsions probably form
thin films and ultimately disappear, whereas " mousses " containing
5 0 4 0 % water remain as a film over I mm thick. The 30 000 toils of
oil which were converted into " mousse " and polluted the north coast
of Brittany on 1 1 April 1967 were spilt from the " Torrey Canyon "
on 18-20 March and followed an irregular course eastwards for about
140 miles, touching Guernsey on 7 April before drifting south over the
remaining 40 miles. A further 40 000-50 000 tons, released on 26-30
March, moved southwards from about 2 April for nearly 200 miles,
passing Ushant on 1 7 April and penetrating well into the Bay of
Biscay by 1-3 May. After apparently successful sinking operations, a
small quantity eventually reached the south coast of Brittany on 1920 May (Smith, 1968).
When the slick reaches the coast, its behaviour depends on the
nature both of oil and shore. In all but the heaviest pollution, much
of the oil will be carried to the strandline along high-water mark by
successive tides. Well-weathered or heavy oils become mixed with
mineral or vegetabIe particles during this process, forming the oil-cakes
mentioned above. Those which are thin, because freshly spilt or by
the action of hot sun, may cause greater trouble by sinking into sand
and shingle or clinging to seaweeds. The most troublesome beach to
A. NELSON-SMITH
allowance should be given for strong ocean or tidal currents. Calculations made when plotting the drift of " Torrey Canyon " oil showed it
to move in the direction of the wind at about 3.4% of its speed (Smith,
1968). This agrees well with measurements of surface drift in the
Atlantic made by Hughes ( I 956), using floating plastic envelopes which
travelled with the wind at 3.3% of its velocity. An oil-slick released
experimentally in Japanese waters travelled at 4% wind speed (reported by Brockis following Berridge et al., 1968a) while the German
Hydrographic Institute, plotting the movement of oil from the " Gerd
Maersk " after her accident in the North Sea in 1955, showed that it
moved a t about 4.2% wind speed (Tomczak, 1964). Earlier experiments
at sea off the United States in 1926-27 and off the British Isles in 1952
are referred to in the Faulkner Report (Ministry of Transport, 1953).
Slicks were followed for 90 miles over 72 h during the American experiment, when it was concluded that most persistent oils will form an
invisible film and thus " disappear " within 100 h of discharge; the
British experimenters tracked a slick for 20 miles over eight days.
Evidence from the Department of the Government Chemist, appended
to the Report, suggests that even very thin films can build up on a
windward shore to cause appreciable pollution. Berridge et nl. (1968b)
report that emulsions containing less than 50% water appear, on
casual inspection, to be undiluted oil. These emulsions probably form
thin films and ultimately disappear, whereas " mousses " containing
5 0 4 0 % water remain as a film over I mm thick. The 30 000 toils of
oil which were converted into " mousse " and polluted the north coast
of Brittany on 1 1 April 1967 were spilt from the " Torrey Canyon "
on 18-20 March and followed an irregular course eastwards for about
140 miles, touching Guernsey on 7 April before drifting south over the
remaining 40 miles. A further 40 000-50 000 tons, released on 26-30
March, moved southwards from about 2 April for nearly 200 miles,
passing Ushant on 1 7 April and penetrating well into the Bay of
Biscay by 1-3 May. After apparently successful sinking operations, a
small quantity eventually reached the south coast of Brittany on 1920 May (Smith, 1968).
When the slick reaches the coast, its behaviour depends on the
nature both of oil and shore. In all but the heaviest pollution, much
of the oil will be carried to the strandline along high-water mark by
successive tides. Well-weathered or heavy oils become mixed with
mineral or vegetabIe particles during this process, forming the oil-cakes
mentioned above. Those which are thin, because freshly spilt or by
the action of hot sun, may cause greater trouble by sinking into sand
and shingle or clinging to seaweeds. The most troublesome beach to