Note: Descriptions are shown in the official language in which they were submitted.
CA 02794933 2016-03-22
1
An icebreaking vessel
The invention relates to a vessel with an icebreaking hull to eliminate ice or
to render
ice harmless in a surface area of water in proximity of an off-shore
installation.
The vessel is for breaking ice drifting in a predominant direction relative to
an off-
shore installation such as eg a drilling vessel. The ice drifts with the
current, but it is
also influenced by the wind.
It is very important that off-shore installations in ice-filled waters are
protected against
the impacts of the ice. For instance, an oil or gas platform may be concerned.
In the following description, a drilling vessel will be used as an example of
an off-
shore installation. Upon impact, a drilling vessel must usually not be shifted
more
than about 2 % of the depth of the water before the drilling operation has to
be
discontinued, and, if it is shifted more than about 5 %, the drill pipe must
usually be
disconnected. It is therefore to be understood that impacts from ice, in
particular in
shallow waters, are extremely critical. Under no circumstances should large
pieces of
ice be allowed to hit the drilling vessel.
It is known within the prior art to use several, typically three, powerful
icebreakers
that cooperate (ice management) to ensure that large chunks of ice cannot
drift
towards the platform or that the ice is not capable of packing around it.
Pack ice and ridged ice are the types of ice that it takes the largest amount
of energy
to avoid. It is assumed that by means of conventional icebreakers it may be
necessary with a machine power of upwards of 60-70 Megawatt, when the ice is
thick
and the current is heavy. That magnitude of machine power is comparable with
nuclear-powered vessels, and in view of the fact that three vessels are often
used, it
will be understood that it is extremely resource-demanding and cost-intensive
to
secure a drilling vessel against the impacts of the ice.
It is desirable to provide a vessel which is considerably more resource-saving
than
the prior art.
CA 02794933 2016-03-22
2
In one aspect this may be provided by the opening through which the anchor
line
travels being located below (deeper than) the propeller shaft of the vessel.
By locating the opening through which the anchor line travels outwards below
sea
level, it is accomplished that the anchor line is not impacted by the ice, and
hence the
torquing on the vessel is avoided which might otherwise occur as a consequence
of
the ice influencing the anchor line.
According to the prior art one would, when one tethers a vessel to an anchor,
secure
the anchor line to the vessel at a large distance from the natural pivot point
of the
vessel. Thereby one hopes that the vessel will ¨ due to the momentum created
thereby between point of attachment and pivot point ¨seek to maintain a fixed
orientation relative to the ice/current or wind that influences the vessel.
By positioning the opening in the vessel and there below, the anchor line is
furthermore located in closer proximity to the natural pivot point of the
vessel, and
thereby it is accomplished that the above-referenced momentum is minimized
whereby it becomes easier to freely select a suitable orientation of the
vessel, while
the latter ¨ under the influence of the forces from the anchor - is moved
through the
ice, transversally to the direction of movement thereof and across the bed of
the
water under the influence of the ice.
According to an embodiment of the vessel, the opening through which the anchor
line
travels into the water is arranged ¨ substantially ¨ halfway between the
midpoint of
the vessel (ie the midpoint of the vessel in the longitudinal direction
thereof, which is
also designated the midship point) and the stern of the vessel.
Positioning of the opening in that place means that the vessel needs less fuel
for
manoeuvring, while simultaneously a sufficiently straightening momentum is
maintained between the opening and the natural pivot point of the vessel.
In this embodiment, the vessel may thus be moved across a surface area of the
water without the ice influencing the anchor line and without the need for
CA 02794933 2016-03-22
3
inexpediently much energy for maintaining a course/orientation which is
favourable
for icebreaking.
In practice, the ice also changes direction, and often no one will know in
advance
which direction it will change into. Therefore, the vessel may be equipped to
deploy
two or more anchors. Thereby, the vessel may use to advantage the one or the
other
anchor line for icebreaking. Of course, according to such embodiment, the
vessel
may also use the pull from two or more anchor lines for icebreaking and,
likewise, the
anchor handling winches may ¨ by suitable deployment of several anchors ¨ be
utilised as powering means for moving the vessel transversally to the
direction of
movement of the ice.
According to one embodiment of the invention, the vessel has two openings
arranged
below the water line, and both between the midship point of the vessel (which,
as
explained above is the centre of the vessel) and the stern.
According to one embodiment of the invention, the vessel has two openings
arranged
below the water line and both between the midship point of the vessel and the
bow.
According to one embodiment, an icebreaking supply vessel with one or two
azimuth
propellers is used, ie propellers that can be rotated 3600 about an
essentially vertical
axis. Usually, the vessel has lateral propellers, too, but they play a minor
part
compared to the azimuth propellers, in particular when it is the heel that is
made to
face towards the ice. Thereby the azimuth propellers may, on the one hand,
grind the
ice and, on the other, push the ice chunks away along with the propeller
water.
When the heel is disposed against the ice, the anchor handling winch can be
used to
pull the vessel upwards against the movement of the ice to the effect that
machine
power is used only to grind the ice and to push the ice around the drilling
vessel.
By using vessels according to the invention, a larger number of vessels can be
anchored and operate quite closely to the drilling platform without an
ensuring risk of
them colliding. Thereby the water around the drilling vessel can be kept free
of ice in
CA 02794933 2016-03-22
4
a particularly efficient manner, and much money can be saved on ice-doublings
of
the drilling vessel.
In one aspect, the invention provides a vessel with an icebreaking hull to
eliminate
ice or to render ice harmless in a surface area of water in proximity of an
off-shore
installation, said vessel comprising: an anchor configured to be deployed in
an
anchor line at a distance from the vessel; motive force means that provide
power for
moving the vessel while it is anchored; an anchor handling winch configured to
wind
or unwind the anchor line through a substantially straight internal passage
that
extends from a first opening in the vessel arranged below the motive force
means
and between a mid section of the vessel and one of a bow and a stern of the
vessel
through to a second opening arranged in a top most deck of the vessel, wherein
the
hull is a mono hull and the first opening is arranged in a flat portion
defined on bottom
of the hull; wherein the bow and the stern of the vessel are equipped with a
portion
configured to break ice upon contact with the portion so that the vessel is
capable of
performing icebreaking tasks while it is anchored, said vessel being, by the
motive
force means or the anchor handling winch, movable across a surface area of the
bed
of the sea, which has a significantly larger expanse than the expanse of the
vessel,
while anchored, whereby the vessel is capable of eliminating or rendering the
ice
harmless in a surface area of the sea.
The invention also relates to a method. In one aspect, the invention provides
a
method for breaking ice in proximity of an off-shore installation, comprising:
providing
a vessel that includes: an anchor which can be deployed in an anchor line at a
distance from the vessel; an anchor handling winch configured to wind or
unwind the
anchor line through a substantially straight internal passage that extends
from a first
opening in the vessel arranged below a motive force means and between a mid
section of the vessel and one of a bow and a stern of the vessel through to a
second
opening arranged in a top most deck of the vessel, wherein the hull is a mono
hull
and the first opening is arranged in a flat portion defined on a bottom of the
hull;
motive force means the provide power for moving the vessel while it is
anchored,
wherein the bow and the stern of the vessel are equipped with a portion
configured to
break ice upon contact with the portion so that the vessel is capable of
performing
icebreaking tasks while it is anchored, said vessel being movable across a
surface
CA 02794933 2016-03-22
=
area of the bed of the sea, which has a significantly larger expanse than the
expanse
of the vessel, while anchored, whereby the vessel is capable of eliminating or
rendering the ice harmless in a surface area of the sea; positioning the
vessel at a
distance from the off-shore installation and in a direction which, as seen
from the off-
5 shore installation, is substantially in parallel with the direction of
movement of the ice
to the effect that the vessel is capable of breaking ice drifting towards the
off-shore
installation, deploying the anchor in the anchor line which is conveyed
through the
internal passage in the vessel and out through the opening which is arranged
under
the sea level, positioning the vessel such that a holding force of the anchor
can be
transferred from the anchor to the vessel via the anchor line and the anchor
handling
winch, adjusting the direction of the anchor line and/or its length via
machinery and/or
the anchor handling winch of the vessel to the effect that the vessel can be
moved
across a surface area of the sea bed which has a considerably larger expanse
than
the expanse of the vessel, whereby the vessel is capable of eliminating ice
and/or
rendering ice harmless in a surface area of the water.
The text mentions the use of azimuth propellers; of course, they can also be
other
means providing motive force/thrusters/propellers known to the person skilled
in the
art.
By the phrase "expanse of the vessel" is intended the area comprised by:
= the largest length of the vessel, and
= the largest width of the vessel.
The largest length and the largest width of the vessel are also designated:
L.O.A.
The invention will now be explained in further detail with reference to a
number of
embodiments, reference being made to the drawing, wherein:
Figure 1 illustrates the prior art;
Figure 2 shows an embodiment of a method for ice management;
Figure 3 shows an alternative embodiment of a method for icebreaking within a
given
area; while
CA 02794933 2016-03-22
6
Figure 4 shows yet an embodiment; while
Figure 5 illustrates ice management with three vessels;
Figure 6 shows an embodiment of a vessel according to the invention;
Figure 7 shows an embodiment of the invention executed on a vessel comprising
a
so-called "skeg"; and
Figure 8 shows a vessel as shown in figure 6, seen from above.
Figure 1 shows a drilling vessel 1 in Arctic waters. The drilling vessel is
retained by
means of eg eight anchors. The associated anchor lines are illustrated by
means of
the eight arrows in the figure. Figure 1 also shows a number of large ice
floes Fl, F2
and F3 that are broken by means of icebreakers 2, 3 and 4 to the effect that
only
relatively few and small chunks of ice K1, K2 and K3 drift along and past the
drilling
vessel, since the ice drifts in the direction of the shown arrow P. If an ice
floe the size
of floes Fl, F2 or F3 hits the drilling vessel, the anchors thereof cannot
uphold the
requisite, exact position.
Icebreakers 2, 3 and 4 are in mutual communication with one another to obtain
the
most efficient icebreaking possible. However, this does not prevent the energy
consumption onboard the three vessels to be high, see the explanation of this
in the
introduction. The invention entails a considerable reduction in the
consumption of
resources necessary for breaking the ice sufficiently.
Figure 2 illustrates a method whereby a vessel 5, eg an ice-breaking supply
vessel,
goes sailing and sets an anchor 6 to the effect that the vessel 5 will go in
the
direction of the drilling vessel 1 when the anchor line is deployed. The
anchor line
may typically have a length of 1000 m (depending on the depth of water, but
typically
it is three times the depth of water). The ice moves essentially in the
direction of the
arrow P, but for the sake of overview it is not shown in figure 2.
CA 02794933 2016-03-22
=
7
The mere fact that the vessel 5 is still without active motive-power machinery
will
entail that the ice which is moving towards the drilling vessel 1 is broken.
It will
appear from the figure that the vessel turns the heel towards the ice, and by
means
of a pair of fixed propellers, it is easy to turn the vessel relative to the
direction of
movement of the ice (see below) and to thereby use to advantage the pressure
exerted by the ice to shift the vessel 5 transversally of the direction of
movement of
the ice. In certain conditions, one single vessel operating in this manner
suffices for
protecting the drilling vessel 1.
Figure 3 shows an alternative or a supplementary method for shifting the
vessel 7 in
the transverse direction to the effect that a sufficiently wide belt is
provided where the
ice is rendered harmless. This is done by deployment of two anchors 8 and 9
and by
utilizing the anchor handling winches of the respective anchor lines to
balance the
forces in and the lengths of the anchor lines to the effect that such measure
contributes to controlling the position of the vessel. By simultaneous use of
propellers, the captain has many options for breaking the ice optimally.
According to one embodiment one (or more) icebreaking supply vessel(s) is
(are)
used that are provided with an azimuth propeller at both sides in the stern of
the
vessel. Those propellers that can be rotated 360 are particularly efficient
for use in
the exercise of the method according to the invention. When the anchor line
holds
the vessel up against the pressure of the ice, the propellers can be set in a
transverse position to the effect that they both press the one side of the
vessel
towards the ice, the propeller close to the ice crushing it, while the other
disposes of
the ice with the propeller water.
Figure 4 shows a further, alternative embodiment, wherein two supply vessels
10, 11
are used that are anchored by each their anchor 12 and 13, respectively. In
this way,
the width of the belt where the ice has been rendered harmless is widened, and
it is
noted that it is possible to situate the vessels 10, 11 fairly close to the
drilling vessel 1
without an ensuing risk of them colliding with each other as the very large
forces in
the direction of movement of the ice are absorbed by the respective anchor
lines
which are essentially parallel.
CA 02794933 2016-03-22
=
8
Fig 5 illustrates ice management by means of a method.
The drilling vessel is still shown by 1, but now three icebreaking supply
vessels 14,
15 and 16 are used that are anchored by means of respective anchor lines 17,
18
and 19, respectively. The figure also shows three large floes of ice 20, 21
and 22.
The small chunks of ice are not shown. They were crushed by the six azimuth
propellers of the three vessels to a size which is harmless for the drilling
vessel 1.
The middle vessel is retained by its anchor line 18 and grinds ice off the ice
floe 22
which is pushed away by the propeller water. The outermost vessels 14 and 16
also
machine the ice floe 22 simultaneously with the floes 20 and 21 being pushed
to
each their side, around the drilling vessel 1. In this manner, the water
around the
drilling vessel can be kept free from ice to such degree that it is not
necessary to ice-
double the drilling vessel significantly. Thereby further economies can be
obtained by
the method according to the invention in addition to the great economies
obtained on
fuel and the ensuing reduction of pollution.
Of course, it is common that the direction of the current/the ice changes. It
may
therefore also be necessary to move anchors and vessels to continuously
eliminate
2 0 ice and/or render ice harmless around an off-shore installation. In
order to monitor
the movement of the ice, it is an option to deploy, in an area around the off-
shore
installation, one or more GPS apparatuses (loggers) ¨ known per se ¨ on the
ice.
Thus, by means of the GPS apparatuses, it is possible to monitor the movement
of
the ice around the off-shore installation and to obtain a (an early) warning
of
substantial changes to the direction of movement of the ice. Thereby it is
also
possible to issue a warning about and to implement movement of anchors in due
time to the effect that it is possible to continuously render the ice harmless
(or to
keep the sea completely free from ice) around the off-shore installation.
3 0 Figure 6 is a schematic sectional view of an embodiment of a vessel
according to the
invention.
The vessel comprises a bow (51) and a stern (52), both of which are configured
with
an icebreaking portion (54, 55). They are separated by and are situated above
the
CA 02794933 2016-03-22
9
most deeply situated part of the vessel which ¨ in the embodiment shown, is
the so-
called flat bottom (53) ¨ in the horizontal plane.
In the stern of the vessel, an internal passage (60) is shown which ¨ in the
embodiment shown ¨ contains an anchor line 61. At the one end, the anchor line
is
wound around an anchor handling winch/wheel (62) and, at the other end, it is
attached to an anchor (not shown). According to one embodiment of the
invention,
the opening through which the anchor line passes out into the water is located
as far
towards the stern as possible in the flat bottom of the vessel. As far towards
the stern
as possible usually means so far towards the stern that the opening is caused
to be
further up than the horizontal plane of the flat bottom.
This text uses the term anchor handling winch/wheel which is different from a
conventional capstan in that it is usually designed for far greater forces
than
conventional capstans. Thus, an anchor handling winch may exert pulls of 600-
1000
tons (corresponding to about 6,000,000-10.000,000 Newton) and have a braking
power of 1,000-1,500 tons (corresponding to about 10,000,000-15,000,000
Newton).
The vessel comprises one or more thruster(s) (50) arranged in the stern of the
vessel
(52.) In the shown embodiment, the thruster is journalled rotatably about an
axis (90).
Of course, vessel and thruster (s) may also be made such that one or more
thruster
(s) is (are) not rotatable.
For the sake of stability as well as performance, the thrusters of the vessel
are
arranged such that the propellers are located above the horizontal plane of
the flat
bottom. It is realised by the invention that an anchor line can be conveyed
out
through that part of the bottom which is below the vessel's propellers
(thrusters)
without the line thereby coming into contact with the vessel's stern
propellers
(thrusters).
Figure 7 shows an embodiment of the invention executed on a vessel comprising
a
so-called "skeg" (70), whose functionality will be described in the following.
CA 02794933 2016-03-22
For the sake of good order, it should be mentioned initially that the vessel
depicted in
figure 7 is actually not an icebreaker, and that the depiction serves to
explain the
functionality of a "skeg".
5 To increase the performance of the stern propellers of an icebreaking
vessel, they
are, in a corresponding manner (as shown in in figure 7), sometimes arranged
such
that a part of the propellers or their blades go deeper into the water than
the flat
bottom (60) of the vessel. Such vessels are often made with a lowered bottom
part
called the skeg. The skeg is situated in front (seen relative to the normal
direction of
10 sailing of the vessel). The purpose of a skeg is to protect the propellers
in shallow
waters since "the skeg" will prevent the propellers from hitting the bottom in
case of a
grounding, if any.
An actual icebreaking vessel can thus be made with "skeg" as shown in figure
7, and
in such vessels the invention can be executed by allowing the anchor line to
pass
into the water from a point in "the skeg" that is situated below (deeper than)
the
vessel's propellers (thrusters).
Hereby it will be obvious to the person having skills within this art that a
vessel with
an icebreaking hull can be provided with a skeg. It is thus also possible to
configure it
with a passage for anchor line, wherein the opening conveying the anchor line
into
the water is arranged in "the skeg" and, more specifically, also to the rear
thereof
(towards the stern), as shown in figure 7. Also with the modifications that
are within
the ordinary skills of the person skilled in the art.
Figure 8 shows a vessel as shown in figure 6, seen from above. Centrally of
the
vessel, an anchor handling winch (62) is shown which is coupled to an anchor
(not
shown) via an anchor line (61) extending via an internal passage (outlined
behind the
funnel) and further out through an opening (not shown either) in the bottom of
the
vessel.
As will appear from figure 8, the anchor line extends from the anchor handling
winch
into a funnel-like part (80). The purpose of that part (80) is to convey the
anchor line
from the winch and into the internal passage (shown in dotted lines) which
extends
CA 02794933 2016-03-22
11
through the vessel and out through the bottom thereof. The shape of the funnel-
like
part may of course be varied within the ordinary skills of the person skilled
in this art;
the essential aspect being that the funnel-like part is capable of capturing
the anchor
line from the entire width of the anchor handling winch and of conveying it
into the
internal passage of the vessel.
Other aspects of the invention are:
According to a first aspect of the invention, it is a method in the breaking
of ice
drifting with a predominant direction relative to an off-shore installation,
characterized in that, by means of a vessel, an anchor is deployed in a
position at a
distance from the off-shore installation and in a direction with is, as seen
from the
off-shore installation, substantially in parallel with the direction of
movement of the
ice; and that the machinery of the vessel is used to adjust the direction of
the anchor
line.
According to a second aspect of the invention, it is a method like in the
first
embodiment, characterized in that a vessel is used, wherein the machinery
comprises one or more azimuth propellers.
According to a third aspect of the invention, it is a method like in the first
or the
second aspect, characterized in that a vessel is used, wherein the machinery
comprises side propellers.
According to a fourth aspect of the invention, it is a method like in the
first to third
aspects, characterized in that the machinery is used to adjust the direction
of the
vessel relative to the direction of the anchor line.
According to a fifth aspect of the invention, it is a method like in the first
to fourth
aspects, characterized in that the vessel is turned such that the heel is
facing
towards the ice.
CA 02794933 2016-03-22
12
According to a sixth aspect of the invention, it is a method like in the fifth
aspect,
characterized in that the anchor handling winch is used to pull the heel of
the vessel
upwards against the ice.
According to a seventh aspect of the invention, it is a method like in the
first aspect,
characterized in that several anchors are deployed in dissimilar directions
relative
to the off-shore installation.
According to an eighth aspect of the invention, it is a method like in the
first to
seventh aspects, wherein a number of GPS apparatuses are deployed on the ice,
upstream of and at a distance from the off-shore installation, characterized
in that
information received from thenGPS apparatuses are used to detect a change in
the
direction of movement of the ice; and that this information is used to decide
whether
one or more anchors are to be moved.
Any of these aspects can be combined with the invention as set forth according
to
claim any of the claims.
=
