Full resolution (JPEG) - On this page / på denna sida - The Öresund Power Cable of 1958, by Anders Bergman, Wilhelm Carlshem and Gottschalk von Geijer
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Fig. 5. Landing operation.
The distance from the anchorage to the Swedish
shore was about 770 metres. At 05.25 hrs the mist
dispersed and the sun appeared. The mist still lay over
Öresund shortly before 06.00 however. At the same
time the wind veered to the south-east and began
to increase slightly. The work was interrupted
pending new weather reports. These were not so
favourable as before. Nevertheless, after the forecast had
been checked at 07.00 the weather conditions were
considered sufficiently favourable to allow the
work to be continued. Paying out the cable was
recommenced at 07.30 and was carried out quickly.
At 09.30 the end of the cable had been brought
ashore on the Swedish side. Fixing the cable end
occupied a relatively long time on account of the
constantly increasing current and wind. At 12.30 the
cable end had been connected and sinking of the
shore cable began. This operation was completed
at 13.20 and at 13.30 towing of the drum began.
In the meantime the wind had increased to 10—12
metres per second and the sea had become choppy.
At the same time the current had increased to 2—3
knots. In order to maintain the towed cable in a
straight line the towed section had to be supported
by the auxiliary vessels. The average speed attained
during the crossing of the straits was about 1 knot
and the crossing took 2 hours, the Danish shore
being reached at half-past three p.m. During the
crossing visibility was very poor at times, which
prevented the simultaneous use of the beacon marks
on the two shores part of the time. Under these
conditions the Decca system could be employed for
navigation. On reaching the Danish shore the cable
was laid out on oil barrels along the shore. The
cable was then cut and the remaining part, together
with the drum, was towed to one side. This
operation was completed at 21.00 hrs. After the Danish
shore had been reached the wind dropped and
towards evening conditions of dead calm set in,
with perfect visibility. After the cutting, the floating
cable end was drawn ashore, the oil barrels were
removed and the work of sinking the cable began.
This operation took 3 hours and was completed at
24.00. For the last three hours work was carried
on under the illumination of searchlights. The
distance from shore to shore over the cable route had
been measured by triangulation to 5 169 metres. The
calculated length of cable required for laying was
5 270 metres and this length had been ordered. The
drum, however, actually held about 5 400 metres,
the last hundred metres having been added by
Sieverts Kabelverk as a reserve. After checking the
length of cable laid, it was found that 5 270 metres
had been used. It may be said, therefore, that about
one hundred metres represent slack, that is to say,
2 % of the total cable length. This must be regarded
as satisfactory from the viewpoint of raising the
cable for repairs if necessary.
Shore protection
In order to protect the cable against grinding ice
near the shores, it has been laid in a trench. In
order to sink the cable to a sufficient depth in the
trench on the Swedish side, in addition to sand
suction it was also necessary to resort to blasting.
The trench was formed about 5 metres to the side
of the cable to avoid damaging. The clearing of the
cable trench was carried out by a small bucket
excavator and a sand-suction device. The trench
is 100 metres in length and the depth from the
surface of the water to the bottom at the end points
has been calculated to about 1.5 metres. After
laying the cable in the trench and filling up the latter,
the whole line was covered with cement sacks. As a
protection against grinding ice outside the trench
the cement sack covering has been continued down
to a depth of 2.5 metres which represents a distance
of 200 metres from the shore. The arrangements for
the shore protection of the cable were much simpler
on the Danish side. There it was possible to
construct a trench with the sand-suction device, in
which the cable was laid with the help of
conventional divers. Here too, cement sacks were employed
as a covering.
Theodolite measurements
To provide an additional check that the floating
drum did not deviate from the straight line to any
great extent two theodolites were set up on the
Swedish shore. One of them was located 30 metres
to the north of the straight line and the other 30
metres to the south of it. On the Danish side two
coloured posts placed 60 metres apart were arranged
symmetrically around the straight line. Two similar
.124 ELTEKNIK 1959
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