It is very important that offshore installations in ice-filled waters are protected against the impacts of the ice. For instance, an oil or gas platform may be concerned. Typically, floating ice drifts with the current, but it is also influenced by the wind. The ice may come in large chunks or pieces, or ice floes, which can cause damage to ocean-going vessels and offshore platforms such as a drilling platform or drilling vessel. Further, it is known that coherent ice floes normally have greater strength than ice floes that are broken or partially broken.
In order for a large drilling vessel to operate, it must not be significantly affected or damaged from impact by drifting ice floes. 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 to manage ice and ensure that large chunks of ice cannot drift towards the platform or that the ice is not capable of packing around it. These vessels utilize their own motive power.
Pack ice and ridged ice are the types of ice that require the largest amount of energy to avoid. It is assumed that by means of conventional icebreakers it may be necessary to use machine power of upwards of 60-70 Megawatts, 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.
The object of the invention is to provide a vessel which is considerably more resource-saving than the prior art.
According to one aspect of the invention, a method is provided for the breaking of ice drifting with a predominant direction relative to an offshore installation, such that, by means of a vessel, an anchor is deployed in a position at a distance from the offshore installation and in a direction which is, as seen from the offshore installation, substantially in parallel with the direction of movement of the ice. The machinery of the vessel is used to adjust the direction of the anchor line.
In another aspect of the invention, a method is provided wherein a vessel having one or more azimuth propellers and/or side propellers are used to assist in icebreaking tasks.
In yet another aspect of the invention, winch machinery is used to adjust the direction of the vessel relative to the direction of the anchor line.
In yet another aspect of the invention, the vessel is turned such that the heel is facing towards the ice.
In another aspect of the invention, several anchors are deployed in dissimilar directions relative to the offshore installation.
In yet another aspect of the invention, a plurality of vessels are used and deployed in various anchored positions relative to the offshore installation.
In another aspect of the invention, the opening through which the anchor line travels being located below (deeper than) the propeller shaft or other drive members of the vessel.
According to another aspect of the invention, a number of GPS apparatuses are deployed on the ice, upstream of and at a distance from the offshore installation, so that information received from then GPS 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 and vessels are to be moved.
The invention will now be explained in further detail with reference to a number of embodiments, reference being made to the drawing, wherein:
Most of the present embodiments below incorporate one or more vessels that include at least a first opening through which an anchor line may pass into the water. This opening is placed on a lower point of the hull of the vessel that is located under (deeper than) the vessel's submerged portion of the propeller shaft and/or propeller. In other embodiments, at least a plurality of openings are provided. As an example, the first opening is located along a longitudinal length of the vessel, such as a centerline, between an approximate midpoint of the vessel and the stern. The other opening is located between this midpoint and the vessel's bow. By providing the vessel with two openings located in these positions or approximate thereto, the vessel may be manipulated and oriented using power of anchor line winches so that it is positioned in the best way relative to flowing ice, such as with the vessel turning its heel, bow or starboard or lateral sides towards the oncoming ice flow.
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 (i.e. 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 maneuvering, 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 expending much energy for maintaining a course/orientation which is favorable for icebreaking.
In practice, the ice also changes direction, and it is difficult if not impossible for operators to know in advance which direction it will change to. 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 utilized as powering means for moving the vessel transversally to the direction of movement of the ice. Further, by locating the opening through which the anchor line travels outwards below sea level, 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 impinging on the anchor line.
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 stern.
According to another 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 another embodiment, an icebreaking supply vessel with one or two azimuth propellers is used, i.e. propellers that can be rotated 360° about an essentially vertical axis. Usually, the vessel has lateral propellers, but such drives 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, serve to 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 a particularly efficient manner, and much money can be saved on ice-doublings of the drilling vessel.
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 “LOA.”
Turning now to the drawings,
Icebreakers 20, 120, 220 are typically 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, through use of high power through each vessel's motive power drives, such as heavy diesel engines. The present invention results in a considerable reduction in the consumption of resources necessary for breaking the ice sufficiently.
As vessel 20 operates without its active motive power drive and remains anchored in place, 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 20 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.
According to another embodiment, one or more icebreaking supply vessels 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 and grinding it, while the other disposes of the ice away from the vessel using its propeller water.
The middle vessel is retained by anchor 5 and grinds ice off the ice floe 3 which is pushed away by the propeller water. The outermost vessels 20 and 20b also machine the ice floe 3 simultaneously using their respective propellers, although not necessarily their main motive drive systems. Azimuth and side propellers such as those shown schematically may also be used to grind and chop ice, with the floe 3 being pushed to either side to create a zone substantially free of large ice floes 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 ice and/or render ice harmless around an offshore installation. In order to monitor the movement of the ice, it is an option to deploy, in an area around the offshore 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 offshore 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 offshore installation.
It may be appropriate to allow the one vessel 20 to be positioned in place using only its anchor 5 without the use of any supplemental power. In this way, the vessel 20 may break ice to create a safe belt running from the vessel 20 to the offshore platform 1 relatively free of large pieces of ice around the offshore platform 1 as illustrated.
The second vessel 120 is similarly anchored using its anchor 105 as shown, slightly offset from the line extending between the offshore platform 1 and the first vessel 20. This shifted position of the second vessel 120 allows it to perform a similar ice breaking function without the significant use of drive power from the vessel's main motive drive engines. This allows the creation of a larger belt or swath of down towards the offshore platform 1 in the direction of the flow P.
The first vessel 20 therefore serves both to break ice flowing in the flow direction P essentially down toward the offshore installation 1. However, because ice is stronger as a coherent, larger mass, the vessel 20 also weakens the ice pieces by breaking them down, which can extend down toward offshore installation. In an alternate embodiment, therefore, the other vessel 120 can be unanchored to further break the weakened ice for a surface area using a lower degree of motive drive power than would normally be required to break stable coherent ice. By positioning the vessels in these various configurations, economical and efficient icebreaking methods may be applied to individual sets of conditions.
In the present configuration, the first vessel 20 is placed the greatest distance from the offshore installation, and positioned to the left in this aerial view. The cascading right edge of the belt formed in the ice, which is now partially broken up and therefore having less strength, can then be serviced more efficiently by the other vessels 120 and 220. By varying the distances between the vessels and the offshore installation 1, again more efficient icebreaking with a minimum use of propellers or engine power may be conducted.
The vessel comprises a bow 21 and a stern 22, both of which are configured with an icebreaking portion 24 and 25, respectively. They are separated by and are situated above the most deeply situated part of the vessel which—in the embodiment shown, is the so-called flat bottom 23—in the horizontal plane. This lowest portion of the vessel's hull may comprise the keel or other bottom surface of the vessel, whether fully flat or not.
In the stern of the vessel, an internal passage 30 is shown which—in the embodiment shown—contains an anchor line 31. At the one end, the anchor line is wound around an anchor handling power winch/wheel 32 and, at the other end, it is attached to an anchor 33. 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 23 of the vessel. In another embodiment of the invention, the opening may be positioned either midship along the bottom of the vessel or in proximity to the point around which the vessel will pivot naturally.
In another embodiment of the vessel of
When the anchor 33 is firmly planted in the sea floor or attached to some other stable mooring device, the vessel 20 may be held stable in relation to the direction of movement or flow of the larger pieces of ice, or ice floes. The winch 32 may be used to stabilize the boat or allow it to move within a specified range of the anchor, allowing the boat to move relative to the anchor and reducing any additional thrust that might be needed by the vessel's main motive power system.
Also, as noted above, by holding the vessel 20 steady relative to the ice floe, the movement of the ice relative to the anchored vessel can break up the ice into smaller pieces in the same fashion as if the vessel were moving under its own power relative to the ice floe.
This text uses the term anchor handling power 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) 70 arranged in the stern of the vessel 22. In the embodiment shown, the thruster 70 is journalled rotatably about an axis 71. 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, or the bottom-most part of the vessel. It is realized by the invention that an anchor line can be conveyed out through that part of the bottom which is below the vessel's propellers or thrusters, or the portion of any propeller shaft that extends from the hull, without the anchor line thereby coming into contact with these drive structures.
To increase the performance of the stern propellers of an icebreaking vessel, they are, in a corresponding manner (as shown in
An actual icebreaking vessel can thus be made with “skeg” as shown in dotted line partially as item 80
It is thus also possible to configure the skeg 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). Also with the modifications that are within the ordinary skills of the person skilled in the art.
As will appear from
While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.
Number | Date | Country | Kind |
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PA 2010 70136 | Mar 2010 | DK | national |
PA 2010 70465 | Oct 2010 | DK | national |
PA 2011 70154 | Mar 2011 | DK | national |
This application claims the benefit of the filing dates of U.S. Provisional Patent Application Ser. No. 61/319,474 filed on Mar. 31, 2010; Danish Application No. PA 2010 70136 filed on Mar. 31, 2010; U.S. Provisional Patent Application Ser. No. 61/409,677 filed on Nov. 3, 2010; Danish Application No. PA 2010 70465 filed on Oct. 29, 2010; and Danish Application No. PA 2011 70154 filed on Mar. 31, 2011. Each of the above mentioned U.S. provisional applications and Danish applications is incorporated in its entirety by reference herein.
Number | Date | Country | |
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61319474 | Mar 2010 | US | |
61409677 | Nov 2010 | US |