Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention is concerned with the protection of
marine structures threatened by icebergs and growlers and is
particularly concerned with apparatus for and a method of
capturing and towing icebergs and growlers (for the sake brevity
hereinafter referred to generically as "icebergs" where the
context permits~.
Icebergs pose a grave risk to oil and gas rigs off the
east coast of Canada and many techniques have been used to
divert them or destroy them. The most successful approach has
been to capture the icebergs with a rope trailed from a towing
vessel which circles the iceberg and takes up the trailed end of
the rope. In some instances, it has proven possible to capture
growlers with a loop of rope trailed from the towing vessel.
The success of this technique has been limited by the
shape of the iceberg. l~he center of gravity of the iceberg is
well below the surface of the water and as the rope pulls on the
iceberg, it tends to cause the iceberg to roll and the rope
often moves over the top of the iceberg. In many instances, it
has proven impossible to capture an iceberg and in these
instances, it has proven necessary to move the rig which it
threatens and this is an enormously costly and complicated
procedure.
According to one aspect of the present invention, there
is provided a method of protecting a marine structure threatened
by an iceberg which comprises trailing an iceberg capturing
structure from a towing vessel, said structure comprising a net
having a buoyant head rope and a deeply submerged foot rope and
bridle lines connecting the net to the vessel, positioning the
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net so that the iceberg lies between it and the vessel, drawing
the net to capture the iceberg and towing the iceberg to a
non-threatening location.
When capturing a large iceberg it is appropriate that
the iceberg capturing structure should be trailed by the bridle
at one end of the net, the vessel being caused to circle the
iceberg and the other bridle being recovered so that the iceberg
lies within a loop formed by the net and bridles.
To capture a growler the iceberg capturing structure is
trailed as a loop from the vessel and the vessel manoeuvered to
dispose the loop about the growler.
The method preferably includes the step of adjusting
the lengths of the top and bottom lines of the bridles so the
head rope contacts the iceberg before the iceberg is contacted
by the foot rope, in this way to cause the iceberg to roll into
the net between the head rope and the foot rope.
According to another aspect of the present invention,
there is provided apparatus for protecting a marine structure
threatened by an iceberg which comprises a net having a buoyant
head rope and a non-buoyant foot rope, the length of the net
between the head rope and the foot rope being such that when
deployed, the foot rope is disposed below the center of gravity
of an iceberg which is to be captured, and bridles secured to
the ends of the net for connecting the net to a towing vessel.
Most desirably the length of the net between the foot and head
ropes is such that the foot rope is disposed below the iceberg
to be captured. Preferably the net ls reinforced by supports
connected between the head rope and the foot ropeO Additional
reinforcement may be provided extending between the end lines of
the net.
The head rope may be provided with a plurality of
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~loatation devices to support the head rope at the surface of
the water. The foot rope may be of chainO
According to yet another aspect of this invention there
is provided equipment for protecting a marine structure
threatened by an iceberg which comprises a towing vessel, a net
having head and foot ropes, the head rope being buoyant and the
length of the net between head and foot ropes being such that
the foot rope, when deployed, is below the center of gravity of
an iceberg to be captured, and bridles connecting the net to the
vessel.
hmbodiments of the present invention are illustrated,
schematically, in the accompanying drawings in which:
Figure l illustrates an iceberg capturing structure;
Figure 2 is a side view of a vessel in the process of
capturing an iceberg;
Figure 3 shows the iceberg after capture;
Figure 4 shows the manner in which the apparatus of
Figure 1 is used to capture a growler, and
Figure 5, 6 and 7 illustrate the manner in which the
device of Figure l is used to capture an iceberg.
The apparatus of Figure 1 comprises a net lO having a
head rope 12 provided with a plurality of floats 14 and a foot
rope 16 of chain. End lines 18 and 20 interconnect the ends of
the head and foot ropes. The net comprises a mesh indicated at
22 supported by support straps 24 which extend between the head
rope 12 and foot rope 16 and support straps 26 which extend
between the end lines 18 and 20. Bridles 28 and 30 are made up
of top lines 32 and 34 and bottom lines 36 and 38 respectively~
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The top and bottom lines o~ bridle 28 are connected by a shackle
40 to tow line 41 and those of bridle 30 are connected by
shackle 42 to tow line 43. The end lines are typically one
hundred feet long, but of course this will vary with the duty to
which the device is put.
In Figure 2 the bridles, of which only one is
illustrated, are connected, by the tow lines, to a towing vessel
V about to capture an iceberg B. The top line 32 of the bridle
is adjusted so that the head rope 12 of the net first contacts
the iceberg so that the iceberg will tend to roll, as viewed in
the drawings, clockwise so that the iceberg moves towards the
belly of the net. It is to be noted that the foot rope 16 of
the net is disposed below the center of gravity of the iceberg
so that the iceberg will be captured as illustrated in Figure 3
so that it may be towed to safety.
Figure 4 illustrates a technique used for capturing a
growler indicated at G. The vessel V trails the net capturing
structure as a loop with the bridles 28 and 30 being secured to
crash bars 44 and 46 respectively or to any sturdy part of the
vessel V. Iceberg lines ~8 and 50 are trained about winches 52
and 54 respectively. The vessel is manoeuvered to place the tow
line adjacent to the growler and then moves to the side so that
the growler passes the tow line to be disposed within the loop.
The vessel is then moved ahead so that the head rope 12 of the
net contacts the growler above its center of gravity tending to
cause it to roll into the belly of the net.
In Figures 5, 6 and 7 there is illustrated a technique
for using the device of Figure 1 to capture a large iceberg. In
this instance, the net 10 is trailed by bridle 28 with the
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bridle 30 trailing behind the net. If necessary, a messenger
line 56 is secured to bridle 30. As illustrated in Figure 6 the
vessel circles the iceberg B and moves to the position
illustrated in Figure 7 where it recovers messenger line 56.
The bridle 30 is then secured and the vessel moved ahead to
capture the iceberg and thereafter to tow it to safety.
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