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WO2008048164A1 - A method of breaking ice located on a water surface around a semisubmersible ship and a semisubmersible ship - Google Patents

A method of breaking ice located on a water surface around a semisubmersible ship and a semisubmersible ship Download PDF

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Publication number
WO2008048164A1
WO2008048164A1 PCT/SE2007/000905 SE2007000905W WO2008048164A1 WO 2008048164 A1 WO2008048164 A1 WO 2008048164A1 SE 2007000905 W SE2007000905 W SE 2007000905W WO 2008048164 A1 WO2008048164 A1 WO 2008048164A1
Authority
WO
WIPO (PCT)
Prior art keywords
ship
ice
ice breaking
breaking member
deck structure
Prior art date
Application number
PCT/SE2007/000905
Other languages
French (fr)
Inventor
Konstantin Roumeliotis
Original Assignee
Gva Consultants Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gva Consultants Ab filed Critical Gva Consultants Ab
Publication of WO2008048164A1 publication Critical patent/WO2008048164A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
    • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
    • B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/02—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement
    • B63B1/10—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with multiple hulls
    • B63B1/107—Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
    • B63B35/08—Ice-breakers or other vessels or floating structures for operation in ice-infested waters; Ice-breakers, or other vessels or floating structures having equipment specially adapted therefor
    • B63B35/10—Ice-breakers or other vessels or floating structures for operation in ice-infested waters; Ice-breakers, or other vessels or floating structures having equipment specially adapted therefor having forced pitching or rolling equipment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B2211/00—Applications
    • B63B2211/06—Operation in ice-infested waters

Definitions

  • the present invention relates to a method of breaking ice located on a water surface around a semi-submersible ship.
  • the invention relates to a method of breaking ice around a ship having a weight distribution capacity, which ship comprises a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure, wherein, as the ship floats in water with a still water surface, the float is adapted to be located at least partially beneath the still water surface and wherein the deck structure is adapted to be located at least partially above the still water surface, wherein the ship further comprises an ice breaking member, which is fixedly attached to the ship in the area between the float and the deck structure, wherein the ice breaking member comprises an ice breaking panel having a normal direction extending at least partially towards the still water surface, wherein the ice breaking member further comprises an enclosed volume, which is at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume.
  • the method comprises the steps of: - adjusting a floating condition of the ship such that at least a portioji of the ice breaking member is located by the ice, and changing the floating condition of the ship by varying a quantity of liquid in the enclosed volume altering the weight distribution of the ship, resulting in that at least a portion of the ice breaking member moves through the ice, wherein ice in the area of the ice breaking member is broken.
  • the present invention further relates to a semi-submersible ship by which the method according the invention may be carried out.
  • Semi-submersible ships i.e. ships comprising a float, a deck structure and at least one support column extending from the float to the deck structure, is inter alia used for drilling for, or production of, natural resources such as gas and oil, when the natural resources for example are located in a source located at the bottom of a sea or lake. Furthermore, semi-submersible ships are used for quartering staff working out at sea.
  • a semi-submersible ship may be placed on the surface of the sea or lake in the vicinity of the source and the ship is adapted to maintain its geographical position utilizing a positioning system generally comprising a mooring system and/or a propeller system - such a propeller system is generally denoted a thruster system.
  • each ice deflector is in the form of a body which is slidably attached about a support column of the ship.
  • the ice deflector has a relatively large mass and is adapted to slide up and down the support column to thereby break ice around the above-mentioned column.
  • ice deflectors have certain disadvantages. For instance, the use of ice deflectors results in that the ship's centre of gravity is moved upward, since the ice deflectors are located relatively high up on the support columns and need to be appropriately heavy in order to be able to break ice. This displacement of the centre of gravity impedes the stability characteristics of the ship and hence the deck load capacity of the ship. Further, each ice deflector has to be movably arranged on each corresponding column. This may be difficult to ensure, in particular since the ice deflectors are intended to be used in cold and icy conditions.
  • US Patent 4 048 943 discloses an offshore structure, adapted for operation in an ice infested environment.
  • the offshore structure comprises a floating caisson that can be actively heaved in the water to break ice.
  • the caisson comprises a radially tapered upper portion and means for vertically moving the caisson so that the upper portion may pierce and break ice.
  • US Patent 3 939 789 discloses a vessel for use in ice-covered waters which vessel has a motion inducing tank disposed in its hull.
  • the tank extends vertically in the hull from a lower en located below the hull load water line and to an upper end located above the waterline.
  • the tank also comprises ports located at the bottom of the tank and air flow devices. By utilizing the ports and the air flow devices, the quantity of sea water in the tank may be altered, resulting in a change in pitch of the vessel. This change in pitch may be used for breaking ice by the bow of the vessel.
  • One object of the present invention is to provide a method of breaking ice around a semi- submersible ship, wherein the method comprises the use of devices which have a low influence on the stability characteristics of the ship.
  • a second object of the present invention is to provide a method of breaking ice around a semi-submersible ship, wherein the method comprises the use of few moving parts, in particular few moving parts which may be exposed to environmental loads such as from ice.
  • a third object of the present invention is to provide a method of breaking ice around a semi-submersible ship, wherein the method facilitates the ice breaking by loosening up the ice.
  • At least one of the objects above is achieved by a method of breaking ice around a semi- submersible ship according to claim 1.
  • one aspect of the invention relates to a method of breaking ice located on a water surface by a semi-submersible ship having a weight distribution capacity.
  • the ship comprises a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure.
  • the float As the ship floats in water with a still water surface, the float is adapted to be located at least partially beneath the still water surface and the deck structure is adapted to be located at least partially above the still water surface.
  • the ship further comprises an ice breaking member, which is fixedly attached to the ship in the area between the float and the deck structure, wherein the ice breaking member comprises an ice breaking panel which has a normal direction extending at least partially towards the still water surface.
  • still water surface refers to the surface of the water when it is completely still, i.e. the water surface has for instance no wave motions.
  • the ice breaking member further comprises an enclosed volume, which is at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume. Furthermore, the ice breaking member comprises: a fluid opening to the ambient environment, air flow means and an air pipe comprising a valve.
  • the method comprises the steps of: adjusting a floating condition of the ship such that at least a portion of the ice breaking member is located by the ice, and altering the floating condition of the ship by altering the quantity of liquid in the enclosed volume, resulting in that at least a portion of the ice breaking member moves through the ice, whereby ice in the area a the ice breaking members is broken.
  • the step of altering the quantity of liquid in the enclosed volume comprises the step of decreasing the quantity of liquid in the enclosed volume by: closing the valve, and introducing air into the enclosed volume by means of the air flow means, wherein liquid is forced to flow out of the enclosed volume into the ambient environment through the fluid opening.
  • One advantage is that since the ice breaking member in itself comprises a fluid opening to the ambient environment, the ice breaking member does not need to be connected to a piping system feeding water in and out of the enclosed volume. Instead, water may be fed in and out of the enclosed volume via the fluid opening, which thus substantially reduces the need of components of the ice breaking member and thus also reduces the weight of the ship.
  • Another advantage is that when air is blown in to the enclosed volume by means of the air flow means, at least a portion of this air may travel out of the fluid opening and result in that air bubbles are created in the water surrounding the ice breaking member. These air bubbles may travel up towards the lower edge of the ice which is to be broken and thus facilitate the ice breaking work by loosening up the ice from below.
  • the quantity of liquid in the enclosed volume is increased by opening the valve, whereby liquid flows in to the enclosed volume from the ambient environment through the fluid opening.
  • this is advantageous since liquid may be introduced directly into the enclosed volume.
  • ice is broken by the motion and the weight of the ship itself.
  • the ship does not need to be provided with additional weights in order to perform the ice breaking.
  • the ice breaking member is fixedly attached to the ship, preferably no moving parts of the ice breaking member are exposed to outer environmental loads, such as loads from ice.
  • the ice breaking member comprises both an ice breaking panel and an enclosed volume
  • the function of crushing ice is combined with a possibility to vary the weight distribution, by means of the enclosed volume, in one unit, i.e. the ice breaking member.
  • the ice breaking member comprises both an ice breaking panel and an enclosed volume
  • the change of the floating condition comprises a change of an inclination position of the ship.
  • the change of the floating condition comprises also, or instead, a change of the draught of the ship.
  • the ship comprises a plurality of support columns, each one provided with at least one ice breaking member, wherein the floating condition of the ship is changed by varying the quantity of liquid in several of the ice breaking members. In this manner a more rapid change in the floating condition may be obtained at the same time as ice breaking is enabled around each of the support columns provided with an ice breaking member.
  • the normal direction of the ice breaking panel extends at least partially towards the centre plane of the float, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction towards the water.
  • the deck structure has a horizontally extending second centre plane, wherein the normal direction extends at least partially towards the second centre plane, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction from the water.
  • the ice breaking member in addition to an ice breaking panel the normal direction of which extends towards the second centre plane, further comprises a second ice breaking panel having a second normal direction extending out from the ice breaking member.
  • the second normal direction extends at least partially towards the float, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction from the water as when well as the second ice breaking panel is driven through the ice in a direction towards the water.
  • a second aspect of the invention is to provide a semi-submersible ship, by which any of the methods above may be performed.
  • the second aspect of the invention relates to a semi-submersible ship, comprising a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure, wherein the float and the deck structure are defined as above.
  • the ship comprises an ice breaking member, fixedly attached to the ship in the area between the float and the deck structure, the ice breaking member comprising an ice breaking panel extending in a plane having a component which is parallel to the centre plane.
  • the ice breaking panel further has a normal direction extending out from the ice breaking member.
  • the ice breaking member comprises an enclosed volume, at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume in order to change a floating condition of the ship.
  • the control arrangement comprises: air flow means for introducing air into the enclosed volume; an air pipe comprising a valve and a fluid opening to the ambient environment through which fluid opening fluid is allowed to flow.
  • the fluid opening is located in a portion of the ice breaking member located closest to the float.
  • the ice breaking panel extends in a plane forming an angle with the centre plane in the range of 80-20°, preferably in the range of 60-30°, more preferably in the range of 50-40°.
  • an ice breaking panel is obtained which may be oblique, i.e. not parallel, to the ice to be broken. This is advantageous since the ice breaking panel need not then to apply a simultaneous pressure to the area projected on the ice. This is preferred from both a structural point of view for the ice breaking panel, as well as for the force that has to be applied to the ice breaking panel in order to break the ice.
  • the air pipe comprises a first air opening located in the enclosed volume and a second opening to the ambient air, the second air opening being located at a distance from the centre plane which is greater than the distance from a portion of the enclosed volume located at the greatest distance from the centre plane.
  • the second air opening is located on a side of the deck structure facing away from the centre plane. This is an advantageous location of the air opening, since an area located on a side of the deck structure facing away from the centre plane is less likely to be covered with water, whether this be due to changes in the floating condition or due to waves impacting the ship.
  • the normal direction extends at least partially towards the centre plane.
  • the deck structure has a horizontally extending second centre plane, the normal direction extending at least partially towards the second centre plane.
  • the ice breaking member further comprises a second ice breaking panel having a second normal direction extending out from the ice breaking member, the second normal direction extending at least partially towards the centre plane of the float.
  • the ship comprises at least one support column provided with at least one ice breaking member.
  • the ship comprises a plurality of support columns and each support column of the ship is provided with at least one ice breaking member.
  • the ship comprises a guard for protecting drilling equipment from environmental loads, such as wave loads, which guard is located between the deck structure and the float, wherein the guard is provided with at least one ice breaking member.
  • Fig. 1 illustrates a schematic side view of an example of a semi-submersible ship by which the method of the invention may be performed
  • Fig. 2 illustrates a perspective view of a plurality of ice breaking members arranged on a support column of the ship illustrated in Fig. 1;
  • Fig. 3 illustrates a cross-sectional view of an ice breaking member of the ship of Fig. 1 ;
  • Fig. 4 illustrates a cross-sectional view of the ice breaking member of Fig. 3, when the member is emptied of water;
  • Fig. 5 illustrates a cross-sectional view of the ice breaking member of Fig. 3, 5 when this is filled with water;
  • Fig. 6 illustrates a cross-sectional view of another embodiment of an ice breaking member
  • Fig. 7 illustrates an embodiment of a semi-submersible ship according to the present invention
  • Fig. 8 illustrates a further embodiment of a semi-submersible ship according to the present invention
  • Fig. 9 illustrates a cross-sectional view of an alternative embodiment of an ice breaking member, when being emptied of water
  • Fig. 10 illustrates a cross-sectional view of the ice breaking member in Fig. 9, 20 when being filled with water.
  • Fig. 1 illustrates a semi-submersible ship 10 comprising a float 12 having a horizontally extending centre plane 14.
  • the ship comprises a deck structure 16 and at least one support column 18 extending from the float 12 to the deck structure 16.
  • a support column 30 18 generally has the shape of a cylinder the cross-section of which generally is circular or rectangular, although there may of course be other types of cross-sections.
  • the ship 10 in Fig. 1 has four support columns, of which two 18, 20 are visible.
  • the ship 10 in Fig. 1 has a longitudinal extension indicated by an arrow 21 and a vertical extension indicated by arrow 23. As is realized from Fig.
  • the float 12 when the ship is floating in water 22 having a still water surface 24, the float 12 is adapted to be located at least partially beneath the still water surface 24 and the deck structure 16 is adapted to be located at least partially above the still water surface 24. In the position illustrated in Fig. 1 , the whole of the float 12 is located beneath the still water surface 24 and the deck structure is located completely above the still water surface 24.
  • the ship 10 in Fig. 1 further comprises an ice breaking member 26, fixedly attached to the ship 10 in the area between the float 12 and the deck structure 16.
  • an ice breaking member 26 is on a support column 18, even though ice breaking members 26 may be placed at other locations on the ship 10.
  • a support column 18 may be provided with a plurality of ice breaking members 26a, 26b, 26c and 26d.
  • the ice breaking member 26 comprises an ice breaking panel 28 extending in a plane having a component which is parallel to the centre plane 14.
  • the ice breaking member 26 comprises an enclosed volume 32, also denoted tank, which is at least partially defined by the ice breaking panel 28, and a control arrangement 34 for controlling a quantity of liquid 36 in the enclosed volume 32.
  • the ship 10 has a draught resulting in that the ice breaking member 26 is located by the still water surface 24.
  • the ship 10 may however have a plurality of different draughts, depending on for instance outer conditions such as weather and season.
  • the ship 10 illustrated in Fig. 1 could for instance have a smaller draught during seasons with no ice, in order to obtain an increased initial distance (air gap) between the still water surface 24 and the deck structure 16. This is advantageous since the deck structure 16 may be damaged if impacted by waves.
  • the method of the invention proposes that the floating condition of the ship 10 firstly is adjusted so that at least a portion of the ice breaking member 26 is located by the ice 38, i.e. on the same level as the still water surface 24.
  • the ship 10 is already in such a floating condition.
  • the floating condition is then changed by altering the weight distribution of the ship 10 which means that the ship's weight and/or position of the ship's centre of gravity 40.
  • the change of the floating condition results in that the ice breaking member 26 moves vertically with respect to the ice, indicated by arrow 42 in Fig. 1, and a portion of the ice breaking member may thus move through the ice and hence break the ice.
  • the motion of the ice breaking member 26 relative to the ice 38 may be achieved in a plurality of ways.
  • the floating condition of the ship 10 may be changed by forcing an inclination on the ship 10 in a first inclination direction as indicated by arrow 44 in Fig. 1.
  • One way of achieving this inclination may be to transfer ballast water internally within the ship 10, for example between two tanks 46, 48 located at a longitudinal distance 21 from one another.
  • the ship 10 may also be imparted an inclination which is not parallel to the first inclination direction 44 by transferring for instance ballast water between two tanks located at a transverse distance from one another as well, wherein a transversal extension is perpendicular to both the longitudinal 21 and vertical 23 directions.
  • an inclination is obtained which is perpendicular to the first inclination direction 44. Further, an inclination may be forced on the ship 10 in two inclination directions, for instance by transferring ballast water between four tanks, which are all located at a longitudinal and/or transversal distance from one another. For the ship 10 illustrated in Fig. 1 , which has four support columns, this may be achieved by transferring water between four ballast water tanks, each located by a corresponding support column. It should be noted that the method of transferring ballast water internally within the ship is not a part of the method of the present invention.
  • the mentioned inclination may be achieved by moving a weight, for instance constituted by one or several containers (not shown), between different positions on the deck structure 16. This move may for instance be carried out by means of one or several hoisting cranes (not shown).
  • the motion of the ice breaking member 26 relative to the ice 38 may also be achieved by changing the draught of the ship 10, which in Fig. 1 is indicated by arrow 50.
  • This change of draught is preferably performed by pumping sea or lake water into or out of the ship, whereby the water preferably is stored in the ship by utilizing so called ballast water tanks located on or in the ship 10.
  • sea water will be used for water around the ship 10, regardless of whether the ship 10 is located in a lake or at sea.
  • ballast water tanks For the purpose of changing the draught of the ship 10, a plurality of ballast water tanks may be used. However, a preferred procedure of changing the draught is to change the quantity of liquid in the enclosed volume 32 of the ice breaking member 26, which for example means that sea water is pumped into or out of the enclosed volume 32, from or to the ambient water 22.
  • the ice breaking member 26 is provided with a control arrangement 34 for varying the quantity of sea water in the enclosed volume 32.
  • This arrangement may be of a traditional type comprising inlet and outlet pipes for sea water which are connected to at least one water pump, such that water may be pumped into and out of the enclosed volume through the pipes.
  • Fig. 3 illustrates an ice breaking member 26 according to the invention, wherein the control arrangement 34 of which comprises a fluid opening 56 to the ambient environment through which fluid opening 52 fluids are allowed to flow.
  • the fluid opening 56 is located at a preferred position on the ice breaking member 26, namely in the portion of the same located closest to the float, i.e. in this case at the very bottom of the ice breaking member 26.
  • the control arrangement 34 illustrated in Fig. 3 further comprises air flow means 58 and an air pipe 60 comprising a valve 62.
  • the implementation of the air pipe 60 illustrated in Fig. 3 comprises a first air opening 64 located in the enclosed volume 32 and a second air opening 66 to the ambient air, wherein the second air opening 66 is located at a distance from the centre plane 14, which distance is larger than the distance from a portion of the enclosed volume 32 located at the greatest distance from the centre plane 14.
  • the second air opening 66 is preferably at a higher vertical level than the enclosed volume 32. More preferably, and as illustrated in Fig. 3, the second air opening is located on a side of the deck structure 16 facing away from the centre plane 14. Furthermore, it is realized from Fig.
  • the ice breaking member 26 illustrated in Fig. 3 is advantageous to use in order to alter the quantity of sea water in the enclosed volume 32, i.e. the tank of the ice breaking member 26, in a simple manner. How this is done will be explained in the following, utilizing Fig. 4 and Fig. 5. 5
  • Fig. 4 illustrates the ice breaking member in a position where sea water is forced out of the tank 32. This is achieved by firstly closing the valve 62 of the air pipe 60 and that the air flow means 58, which in this case is constituted by an air pump in fluid communication with both the tank and the ambient air, is providing an air flow q air to the tank 32.
  • the air flow means 58 which in this case is constituted by an air pump in fluid communication with both the tank and the ambient air, is providing an air flow q air to the tank 32.
  • the air flow means 58 may comprise a compressor (not shown).
  • the air flow q a i r increases the air pressure in the tank 32 resulting in that water will be forced out through the fluid opening 56 and will be replaced by a cushion of pressurized air. This air cushion will contribute to the displacement of the ship and thus at least a portion of the ship located in the vicinity of the ice breaking member 26 may move
  • the ice breaking member 26 will not rise further above the still water surface 24 than to a position in which the fluid opening 56 is located by the still water surface 24.
  • sea water may be fed to the tank 32 by closing the air flow means 58, i.e. the air pump in this case, and opening the valve 62 of the air pipe 60.
  • Air will then flow through the air pipe 60 resulting in that the air pressure in the tank 32 decreases. This will result in that the air cushion will decrease its displacement, which in turn results in that the ice breaking member will be lowered down in the water and that the tank will again be filled with water.
  • the ice breaking panel 28 is used for breaking ice 38 located in the vicinity of the ice
  • the deck structure 16 has a horizontally extending second centre plane 74.
  • Fig. 6 illustrates an alternative embodiment of the ice breaking member 26, wherein the normal direction 30 of the ice breaking member 26 extends at least partially towards the second centre plane 74. In this manner, a preferred implementation of the ice breaking member 26 is obtained, by which ice 38 may be broken as the ice breaking member 26 is driven through the ice 38 in a direction from the water 22.
  • the process of filling and emptying the tank 32 of sea water as described above with reference to Fig. 4 - Fig. 6 may preferably be used simultaneously for a plurality of ice breaking members 26 located at a distance from one another, they may for instance be located by separate support columns 18, 20 of the ship 10.
  • the tank 32 of each ice breaking member 26 may either be emptied and filled simultaneously, resulting in a change in draught of the ship 10, or the tanks 32 of some ice breaking members 26 may be filled while the tanks 32 of other ice breaking members may be emptied, resulting in an inclination of the ship 10.
  • the ice breaking panel of an ice breaking member may have one of a plurality of shapes, as long as it has a component parallel to the centre plane 14.
  • an ice breaking member 52 may be designed so as to have a ice breaking panel 54 substantially parallel to the centre plane 14.
  • its ice breaking panel 28 extends in a plane forming an angle with the centre plane 14 in the range of 80-20°, preferably in the range of 60-30°, more preferably in the range of 50-40°.
  • the ice breaking panels 28, 54 illustrated in the appended drawings have substantially flat surfaces, it may in some contexts be preferred to provide the ice breaking panels with substantially rough surfaces, for example corrugated or saw-toothed surfaces, thus obtaining an increased friction between the ice breaking member and the ice, which may enhance the ice breaking action.
  • Fig. 1 illustrates a ship 10 wherein a first support column 18 is provided with a first ice breaking member 26. Furthermore, a second support column 20 is provided with a second ice breaking member 52. Preferably, each support column of a ship is provided with at least one ice breaking member. A single ice breaking member may extend around a support column, although it is more preferred to arrange a plurality of ice breaking members, which together extend around the support column, as indicated in Fig. 2.
  • Fig. 7 illustrates a further embodiment of the ship according to the invention comprising a guard 68 for protecting drilling equipment 70 from environmental loads, which guard 68 is located between the deck structure 16 and the float 12, wherein the guard 68 is provided with at least one ice breaking member 72.
  • a ship is illustrated wherein each support column, of which only two 18, 20 are visible, is provided with substantially identical ice breaking members 26, 52, which is a preferred embodiment of the ship 10 according to the invention.
  • Fig. 8 illustrates another embodiment of the ship 10 of the invention, wherein the deck structure 16 has a horizontally extending second centre plane 74. Furthermore, it is realized that the ship 10 illustrated in Fig. 8 comprises ice breaking members 26 having a design which differs from the previously illustrated designs. This implementation is best described with reference to Fig. 9, illustrating a ice breaking member 26 comprising two ice breaking panels 28, 76 wherein one 28 of the ice breaking panels has a normal direction extending towards the second centre plane 74 and the second ice breaking panel 76 has a normal direction 78 extending at least partially towards the centre plane 14 of the float 12.
  • the ice breaking member 26 in Fig. 9 also comprises an enclosed volume 32, also denoted tank, and a control arrangement 34 for controlling the quantity of fluid 36 in the enclosed volume.
  • the control arrangement 34 illustrated in Fig. 9 comprises a fluid opening 56 to the ambient environment, air flow means 58 and an air pipe 60 having a valve 62, which is a preferred embodiment of the control arrangement 34, although other control arrangements 34 are plausible.
  • ice breaking member 26 illustrated in Fig. 9 is that ice 38 may be broken both when the ice breaking member 26 moves in a direction from, i.e. out of, and towards, i.e. in to, the water 22.
  • This advantage is illustrated in Figs. 9 and 10, wherein Fig. 9 illustrates how the ice breaking member 26 breaks ice by means of the second ice breaking panel 76 as the ice breaking means 26 is driven through the ice 38 in a direction towards the water 20 and Fig. 10 illustrates how the ice breaking member 26 breaks ice by means of the ice breaking panel 28 as the ice breaking member 26 is driven through the ice 38 in a direction from the water.
  • the deck structure 16 on the side facing the centre plane 14 may be provided with one or several ice breaking members in areas located at a distance from support columns and guards for drilling structures.

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  • Combustion & Propulsion (AREA)
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Abstract

The present invention relates to a method of breaking ice located on a water surface around a semi-submersible ship having a weight distribution capacity, which ship comprises a float having a horizontally extending centre plane, a deck structure and at least one support column extending from said float to said deck structure, wherein, when said ship floats in water having a still water surface, said float is adapted to be located at least partially beneath said still water surface and said deck structure is adapted to be located at least partially above said still water surface, wherein said ship further comprises an ice breaking member, fixedly attached to said ship in the area between said float and said deck structure, said ice breaking member comprising an ice breaking panel having a normal direction extending at least partially towards said still water surface.

Description

SEMI-SUBMERSIBLE SHIP
TECHNICAL FIELD
The present invention relates to a method of breaking ice located on a water surface around a semi-submersible ship. In particular, the invention relates to a method of breaking ice around a ship having a weight distribution capacity, which ship comprises a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure, wherein, as the ship floats in water with a still water surface, the float is adapted to be located at least partially beneath the still water surface and wherein the deck structure is adapted to be located at least partially above the still water surface, wherein the ship further comprises an ice breaking member, which is fixedly attached to the ship in the area between the float and the deck structure, wherein the ice breaking member comprises an ice breaking panel having a normal direction extending at least partially towards the still water surface, wherein the ice breaking member further comprises an enclosed volume, which is at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume. The ice breaking member further comprises: a fluid opening to the ambient environment, air flow means and an air pipe comprising a valve.
The method comprises the steps of: - adjusting a floating condition of the ship such that at least a portioji of the ice breaking member is located by the ice, and changing the floating condition of the ship by varying a quantity of liquid in the enclosed volume altering the weight distribution of the ship, resulting in that at least a portion of the ice breaking member moves through the ice, wherein ice in the area of the ice breaking member is broken.
The present invention further relates to a semi-submersible ship by which the method according the invention may be carried out.
BACKGROUND OF THE INVENTION
Semi-submersible ships, i.e. ships comprising a float, a deck structure and at least one support column extending from the float to the deck structure, is inter alia used for drilling for, or production of, natural resources such as gas and oil, when the natural resources for example are located in a source located at the bottom of a sea or lake. Furthermore, semi-submersible ships are used for quartering staff working out at sea.
For these purposes, a semi-submersible ship may be placed on the surface of the sea or lake in the vicinity of the source and the ship is adapted to maintain its geographical position utilizing a positioning system generally comprising a mooring system and/or a propeller system - such a propeller system is generally denoted a thruster system.
Should a semi-submersible ship be placed in a position which may be exposed to ice floes, there is a risk that the above-mentioned ice floe may impact the ship, resulting in that the ship will be exposed to ice loads. These loads may, in addition to damaging the ship per se, affect the positioning system in an adverse way by causing an increased load on the components which are part of the positioning system, such as mooring lines and/or propeller systems.
In order to decrease the load from ice floes, prior art proposes that the ship is provided with ice deflectors, wherein each ice deflector is in the form of a body which is slidably attached about a support column of the ship. The ice deflector has a relatively large mass and is adapted to slide up and down the support column to thereby break ice around the above-mentioned column. Such a solution is for example disclosed in US 4,063,428.
However, utilizing the above-mentioned ice deflectors has certain disadvantages. For instance, the use of ice deflectors results in that the ship's centre of gravity is moved upward, since the ice deflectors are located relatively high up on the support columns and need to be appropriately heavy in order to be able to break ice. This displacement of the centre of gravity impedes the stability characteristics of the ship and hence the deck load capacity of the ship. Further, each ice deflector has to be movably arranged on each corresponding column. This may be difficult to ensure, in particular since the ice deflectors are intended to be used in cold and icy conditions.
Furthermore, US Patent 4 048 943 discloses an offshore structure, adapted for operation in an ice infested environment. The offshore structure comprises a floating caisson that can be actively heaved in the water to break ice. The caisson comprises a radially tapered upper portion and means for vertically moving the caisson so that the upper portion may pierce and break ice. Moreover, US Patent 3 939 789 discloses a vessel for use in ice-covered waters which vessel has a motion inducing tank disposed in its hull. The tank extends vertically in the hull from a lower en located below the hull load water line and to an upper end located above the waterline. The tank also comprises ports located at the bottom of the tank and air flow devices. By utilizing the ports and the air flow devices, the quantity of sea water in the tank may be altered, resulting in a change in pitch of the vessel. This change in pitch may be used for breaking ice by the bow of the vessel.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a method of breaking ice around a semi- submersible ship, wherein the method comprises the use of devices which have a low influence on the stability characteristics of the ship.
A second object of the present invention is to provide a method of breaking ice around a semi-submersible ship, wherein the method comprises the use of few moving parts, in particular few moving parts which may be exposed to environmental loads such as from ice.
A third object of the present invention is to provide a method of breaking ice around a semi-submersible ship, wherein the method facilitates the ice breaking by loosening up the ice.
At least one of the objects above is achieved by a method of breaking ice around a semi- submersible ship according to claim 1.
Thus, one aspect of the invention relates to a method of breaking ice located on a water surface by a semi-submersible ship having a weight distribution capacity. The ship comprises a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure.
As the ship floats in water with a still water surface, the float is adapted to be located at least partially beneath the still water surface and the deck structure is adapted to be located at least partially above the still water surface. The ship further comprises an ice breaking member, which is fixedly attached to the ship in the area between the float and the deck structure, wherein the ice breaking member comprises an ice breaking panel which has a normal direction extending at least partially towards the still water surface.
The expression "still water surface" herein refers to the surface of the water when it is completely still, i.e. the water surface has for instance no wave motions.
The ice breaking member further comprises an enclosed volume, which is at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume. Furthermore, the ice breaking member comprises: a fluid opening to the ambient environment, air flow means and an air pipe comprising a valve. The method comprises the steps of: adjusting a floating condition of the ship such that at least a portion of the ice breaking member is located by the ice, and altering the floating condition of the ship by altering the quantity of liquid in the enclosed volume, resulting in that at least a portion of the ice breaking member moves through the ice, whereby ice in the area a the ice breaking members is broken.
According to the invention, the step of altering the quantity of liquid in the enclosed volume comprises the step of decreasing the quantity of liquid in the enclosed volume by: closing the valve, and introducing air into the enclosed volume by means of the air flow means, wherein liquid is forced to flow out of the enclosed volume into the ambient environment through the fluid opening.
By utilizing the inventive method above for decreasing the quantity of liquid, a plurality of advantages is obtained. One advantage is that since the ice breaking member in itself comprises a fluid opening to the ambient environment, the ice breaking member does not need to be connected to a piping system feeding water in and out of the enclosed volume. Instead, water may be fed in and out of the enclosed volume via the fluid opening, which thus substantially reduces the need of components of the ice breaking member and thus also reduces the weight of the ship.
Another advantage is that when air is blown in to the enclosed volume by means of the air flow means, at least a portion of this air may travel out of the fluid opening and result in that air bubbles are created in the water surrounding the ice breaking member. These air bubbles may travel up towards the lower edge of the ice which is to be broken and thus facilitate the ice breaking work by loosening up the ice from below.
In a further preferred embodiment of the invention, the quantity of liquid in the enclosed volume is increased by opening the valve, whereby liquid flows in to the enclosed volume from the ambient environment through the fluid opening. In a similar manner as previously mentioned in connection to the emptying of the fluid, this is advantageous since liquid may be introduced directly into the enclosed volume.
By utilizing the above method, ice is broken by the motion and the weight of the ship itself. Thus, the ship does not need to be provided with additional weights in order to perform the ice breaking. Furthermore, since the ice breaking member is fixedly attached to the ship, preferably no moving parts of the ice breaking member are exposed to outer environmental loads, such as loads from ice.
Further, since the ice breaking member comprises both an ice breaking panel and an enclosed volume, the function of crushing ice is combined with a possibility to vary the weight distribution, by means of the enclosed volume, in one unit, i.e. the ice breaking member. In this manner, an integrated unit is obtained which is attached to the ship in a simple manner.
In a further embodiment of the invention, the change of the floating condition comprises a change of an inclination position of the ship. In another preferred embodiment of the invention, the change of the floating condition comprises also, or instead, a change of the draught of the ship.
In another preferred embodiment of the invention, the ship comprises a plurality of support columns, each one provided with at least one ice breaking member, wherein the floating condition of the ship is changed by varying the quantity of liquid in several of the ice breaking members. In this manner a more rapid change in the floating condition may be obtained at the same time as ice breaking is enabled around each of the support columns provided with an ice breaking member. In a further preferred embodiment of the invention, the normal direction of the ice breaking panel extends at least partially towards the centre plane of the float, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction towards the water.
In another preferred embodiment of the invention, the deck structure has a horizontally extending second centre plane, wherein the normal direction extends at least partially towards the second centre plane, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction from the water.
In a further preferred embodiment of the invention, the ice breaking member, in addition to an ice breaking panel the normal direction of which extends towards the second centre plane, further comprises a second ice breaking panel having a second normal direction extending out from the ice breaking member. The second normal direction extends at least partially towards the float, wherein the method comprises breaking ice in the area around the ice breaking member as the ice breaking panel is driven through the ice in a direction from the water as when well as the second ice breaking panel is driven through the ice in a direction towards the water.
A second aspect of the invention is to provide a semi-submersible ship, by which any of the methods above may be performed.
Thus, the second aspect of the invention relates to a semi-submersible ship, comprising a float having a horizontally extending centre plane, a deck structure and at least one support column extending from the float to the deck structure, wherein the float and the deck structure are defined as above.
The ship comprises an ice breaking member, fixedly attached to the ship in the area between the float and the deck structure, the ice breaking member comprising an ice breaking panel extending in a plane having a component which is parallel to the centre plane. The ice breaking panel further has a normal direction extending out from the ice breaking member. The ice breaking member comprises an enclosed volume, at least partially defined by the ice breaking panel, and a control arrangement for controlling a quantity of liquid in the enclosed volume in order to change a floating condition of the ship. According to the invention, the control arrangement comprises: air flow means for introducing air into the enclosed volume; an air pipe comprising a valve and a fluid opening to the ambient environment through which fluid opening fluid is allowed to flow.
In a preferred embodiment of the ship according to the invention, the fluid opening is located in a portion of the ice breaking member located closest to the float.
In a preferred embodiment of the ship according to the invention, the ice breaking panel extends in a plane forming an angle with the centre plane in the range of 80-20°, preferably in the range of 60-30°, more preferably in the range of 50-40°.
By arranging the ice breaking panel in any of the above manners, an ice breaking panel is obtained which may be oblique, i.e. not parallel, to the ice to be broken. This is advantageous since the ice breaking panel need not then to apply a simultaneous pressure to the area projected on the ice. This is preferred from both a structural point of view for the ice breaking panel, as well as for the force that has to be applied to the ice breaking panel in order to break the ice.
In another preferred embodiment of the ship according to the invention, the air pipe comprises a first air opening located in the enclosed volume and a second opening to the ambient air, the second air opening being located at a distance from the centre plane which is greater than the distance from a portion of the enclosed volume located at the greatest distance from the centre plane. By arranging the second air opening in this manner, the capability of substantially totally filling the enclosed volume with liquid, i.e. completely emptying the enclosed volume of air, is ensured.
In a further preferred embodiment of the ship according to the invention, the second air opening is located on a side of the deck structure facing away from the centre plane. This is an advantageous location of the air opening, since an area located on a side of the deck structure facing away from the centre plane is less likely to be covered with water, whether this be due to changes in the floating condition or due to waves impacting the ship.
In another preferred embodiment of the ship according to the invention, the normal direction extends at least partially towards the centre plane. In a further preferred embodiment of the ship according to the invention, the deck structure has a horizontally extending second centre plane, the normal direction extending at least partially towards the second centre plane.
In a further preferred embodiment of the ship according to the invention, the ice breaking member further comprises a second ice breaking panel having a second normal direction extending out from the ice breaking member, the second normal direction extending at least partially towards the centre plane of the float.
In another preferred embodiment of the ship according to the invention, the ship comprises at least one support column provided with at least one ice breaking member.
In a further preferred embodiment of the ship according to the invention, the ship comprises a plurality of support columns and each support column of the ship is provided with at least one ice breaking member.
In another preferred embodiment of the ship according to the invention, the ship comprises a guard for protecting drilling equipment from environmental loads, such as wave loads, which guard is located between the deck structure and the float, wherein the guard is provided with at least one ice breaking member.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended figures wherein:
Fig. 1 illustrates a schematic side view of an example of a semi-submersible ship by which the method of the invention may be performed;
Fig. 2 illustrates a perspective view of a plurality of ice breaking members arranged on a support column of the ship illustrated in Fig. 1;
Fig. 3 illustrates a cross-sectional view of an ice breaking member of the ship of Fig. 1 ; Fig. 4 illustrates a cross-sectional view of the ice breaking member of Fig. 3, when the member is emptied of water;
Fig. 5 illustrates a cross-sectional view of the ice breaking member of Fig. 3, 5 when this is filled with water;
Fig. 6 illustrates a cross-sectional view of another embodiment of an ice breaking member;
10 Fig. 7 illustrates an embodiment of a semi-submersible ship according to the present invention;
Fig. 8 illustrates a further embodiment of a semi-submersible ship according to the present invention; 15
Fig. 9 illustrates a cross-sectional view of an alternative embodiment of an ice breaking member, when being emptied of water, and
Fig. 10 illustrates a cross-sectional view of the ice breaking member in Fig. 9, 20 when being filled with water.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will be described using examples of embodiments. It should however be realized that the embodiments are included in order to explain principles of the invention 25 and not to limit the scope of the invention, defined by the appended claims.
Fig. 1 illustrates a semi-submersible ship 10 comprising a float 12 having a horizontally extending centre plane 14. The ship comprises a deck structure 16 and at least one support column 18 extending from the float 12 to the deck structure 16. A support column 30 18 generally has the shape of a cylinder the cross-section of which generally is circular or rectangular, although there may of course be other types of cross-sections. The ship 10 in Fig. 1 has four support columns, of which two 18, 20 are visible. The ship 10 in Fig. 1 has a longitudinal extension indicated by an arrow 21 and a vertical extension indicated by arrow 23. As is realized from Fig. 1 , when the ship is floating in water 22 having a still water surface 24, the float 12 is adapted to be located at least partially beneath the still water surface 24 and the deck structure 16 is adapted to be located at least partially above the still water surface 24. In the position illustrated in Fig. 1 , the whole of the float 12 is located beneath the still water surface 24 and the deck structure is located completely above the still water surface 24.
The ship 10 in Fig. 1 further comprises an ice breaking member 26, fixedly attached to the ship 10 in the area between the float 12 and the deck structure 16. As is evident from Fig. 1, a suitable location of an ice breaking member 26 is on a support column 18, even though ice breaking members 26 may be placed at other locations on the ship 10. Further, as may be gleaned from Fig. 2, a support column 18 may be provided with a plurality of ice breaking members 26a, 26b, 26c and 26d.
As is more evident from Fig. 3, the ice breaking member 26 comprises an ice breaking panel 28 extending in a plane having a component which is parallel to the centre plane 14. In other words, as the ship is floating in water having a still water surface 24 in a position when the ice breaking panel 28 is about to break ice 38, the normal direction 30 of the ice breaking panel 28 extends at least partially towards the still water surface 24. As is further evident from Fig. 3, the ice breaking member 26 comprises an enclosed volume 32, also denoted tank, which is at least partially defined by the ice breaking panel 28, and a control arrangement 34 for controlling a quantity of liquid 36 in the enclosed volume 32.
As may be gleaned from Fig. 1 , the ship 10 has a draught resulting in that the ice breaking member 26 is located by the still water surface 24. In some embodiments of the ship 10, the ship 10 may however have a plurality of different draughts, depending on for instance outer conditions such as weather and season. The ship 10 illustrated in Fig. 1 could for instance have a smaller draught during seasons with no ice, in order to obtain an increased initial distance (air gap) between the still water surface 24 and the deck structure 16. This is advantageous since the deck structure 16 may be damaged if impacted by waves.
In order to crush ice floes 38 drifting towards the ship 10, the method of the invention proposes that the floating condition of the ship 10 firstly is adjusted so that at least a portion of the ice breaking member 26 is located by the ice 38, i.e. on the same level as the still water surface 24. In Fig. 1 , the ship 10 is already in such a floating condition. The floating condition is then changed by altering the weight distribution of the ship 10 which means that the ship's weight and/or position of the ship's centre of gravity 40. The change of the floating condition results in that the ice breaking member 26 moves vertically with respect to the ice, indicated by arrow 42 in Fig. 1, and a portion of the ice breaking member may thus move through the ice and hence break the ice.
As may be realized from Fig. 1 , the motion of the ice breaking member 26 relative to the ice 38 may be achieved in a plurality of ways. For instance, the floating condition of the ship 10 may be changed by forcing an inclination on the ship 10 in a first inclination direction as indicated by arrow 44 in Fig. 1. One way of achieving this inclination may be to transfer ballast water internally within the ship 10, for example between two tanks 46, 48 located at a longitudinal distance 21 from one another. The ship 10 may also be imparted an inclination which is not parallel to the first inclination direction 44 by transferring for instance ballast water between two tanks located at a transverse distance from one another as well, wherein a transversal extension is perpendicular to both the longitudinal 21 and vertical 23 directions. If the tanks are located only at a transversal distance from one another, an inclination is obtained which is perpendicular to the first inclination direction 44. Further, an inclination may be forced on the ship 10 in two inclination directions, for instance by transferring ballast water between four tanks, which are all located at a longitudinal and/or transversal distance from one another. For the ship 10 illustrated in Fig. 1 , which has four support columns, this may be achieved by transferring water between four ballast water tanks, each located by a corresponding support column. It should be noted that the method of transferring ballast water internally within the ship is not a part of the method of the present invention.
Optionally, although not a part of the present invention, the mentioned inclination may be achieved by moving a weight, for instance constituted by one or several containers (not shown), between different positions on the deck structure 16. This move may for instance be carried out by means of one or several hoisting cranes (not shown).
The motion of the ice breaking member 26 relative to the ice 38 may also be achieved by changing the draught of the ship 10, which in Fig. 1 is indicated by arrow 50. This change of draught is preferably performed by pumping sea or lake water into or out of the ship, whereby the water preferably is stored in the ship by utilizing so called ballast water tanks located on or in the ship 10. In the description hereinbelow, the expression sea water will be used for water around the ship 10, regardless of whether the ship 10 is located in a lake or at sea.
For the purpose of changing the draught of the ship 10, a plurality of ballast water tanks may be used. However, a preferred procedure of changing the draught is to change the quantity of liquid in the enclosed volume 32 of the ice breaking member 26, which for example means that sea water is pumped into or out of the enclosed volume 32, from or to the ambient water 22. For this purpose, the ice breaking member 26 is provided with a control arrangement 34 for varying the quantity of sea water in the enclosed volume 32. This arrangement may be of a traditional type comprising inlet and outlet pipes for sea water which are connected to at least one water pump, such that water may be pumped into and out of the enclosed volume through the pipes.
However, Fig. 3 illustrates an ice breaking member 26 according to the invention, wherein the control arrangement 34 of which comprises a fluid opening 56 to the ambient environment through which fluid opening 52 fluids are allowed to flow. In the implementation of the fluid opening 56 illustrated in Fig. 3, the fluid opening 56 is located at a preferred position on the ice breaking member 26, namely in the portion of the same located closest to the float, i.e. in this case at the very bottom of the ice breaking member 26.
The control arrangement 34 illustrated in Fig. 3 further comprises air flow means 58 and an air pipe 60 comprising a valve 62. The implementation of the air pipe 60 illustrated in Fig. 3 comprises a first air opening 64 located in the enclosed volume 32 and a second air opening 66 to the ambient air, wherein the second air opening 66 is located at a distance from the centre plane 14, which distance is larger than the distance from a portion of the enclosed volume 32 located at the greatest distance from the centre plane 14. In other words, the second air opening 66 is preferably at a higher vertical level than the enclosed volume 32. More preferably, and as illustrated in Fig. 3, the second air opening is located on a side of the deck structure 16 facing away from the centre plane 14. Furthermore, it is realized from Fig. 3 that the first air opening 64 preferably is located at the top of the enclosed volume 32. The ice breaking member 26 illustrated in Fig. 3 is advantageous to use in order to alter the quantity of sea water in the enclosed volume 32, i.e. the tank of the ice breaking member 26, in a simple manner. How this is done will be explained in the following, utilizing Fig. 4 and Fig. 5. 5
Fig. 4 illustrates the ice breaking member in a position where sea water is forced out of the tank 32. This is achieved by firstly closing the valve 62 of the air pipe 60 and that the air flow means 58, which in this case is constituted by an air pump in fluid communication with both the tank and the ambient air, is providing an air flow qair to the tank 32.
10 Alternatively, or additionally, the air flow means 58 may comprise a compressor (not shown). The air flow qair increases the air pressure in the tank 32 resulting in that water will be forced out through the fluid opening 56 and will be replaced by a cushion of pressurized air. This air cushion will contribute to the displacement of the ship and thus at least a portion of the ship located in the vicinity of the ice breaking member 26 may move
15 upwards. This displacement will proceed until the fluid opening 56 is at the still water surface 24 of the ambient water 22. If the fluid opening 56 is located at the very bottom of the tank 32, as is the case in Fig. 4, the tank 32 in the just mentioned position will be substantially emptied of water. Since the air cushion will not contribute to the displacement of the ship 10 as the fluid opening 56 is located above the still water surface
20 24, the ice breaking member 26 will not rise further above the still water surface 24 than to a position in which the fluid opening 56 is located by the still water surface 24.
From the just mentioned position, sea water may be fed to the tank 32 by closing the air flow means 58, i.e. the air pump in this case, and opening the valve 62 of the air pipe 60.
25 Air will then flow through the air pipe 60 resulting in that the air pressure in the tank 32 decreases. This will result in that the air cushion will decrease its displacement, which in turn results in that the ice breaking member will be lowered down in the water and that the tank will again be filled with water. As the ice breaking member 26 is lowered in the water, the ice breaking panel 28 is used for breaking ice 38 located in the vicinity of the ice
30 breaking member 26. It should be noted that the above mentioned method of lowering the ice breaking member 26 also can be commenced before the fluid opening 56 is located by the still water surface 24, i.e. only a portion of the ice breaking member 26 needs to be lowered in and out of the water. As is apparent from Fig. 7, the deck structure 16 has a horizontally extending second centre plane 74. With reference to this second centre plane 74, Fig. 6 illustrates an alternative embodiment of the ice breaking member 26, wherein the normal direction 30 of the ice breaking member 26 extends at least partially towards the second centre plane 74. In this manner, a preferred implementation of the ice breaking member 26 is obtained, by which ice 38 may be broken as the ice breaking member 26 is driven through the ice 38 in a direction from the water 22.
The process of filling and emptying the tank 32 of sea water as described above with reference to Fig. 4 - Fig. 6 may preferably be used simultaneously for a plurality of ice breaking members 26 located at a distance from one another, they may for instance be located by separate support columns 18, 20 of the ship 10. The tank 32 of each ice breaking member 26 may either be emptied and filled simultaneously, resulting in a change in draught of the ship 10, or the tanks 32 of some ice breaking members 26 may be filled while the tanks 32 of other ice breaking members may be emptied, resulting in an inclination of the ship 10.
As may be gleaned from Fig. 1 , the ice breaking panel of an ice breaking member may have one of a plurality of shapes, as long as it has a component parallel to the centre plane 14. For instance, an ice breaking member 52 may be designed so as to have a ice breaking panel 54 substantially parallel to the centre plane 14. However, in a preferred embodiment of an ice breaking member 26, its ice breaking panel 28 extends in a plane forming an angle with the centre plane 14 in the range of 80-20°, preferably in the range of 60-30°, more preferably in the range of 50-40°. Furthermore, it should be realized that even though the ice breaking panels 28, 54 illustrated in the appended drawings have substantially flat surfaces, it may in some contexts be preferred to provide the ice breaking panels with substantially rough surfaces, for example corrugated or saw-toothed surfaces, thus obtaining an increased friction between the ice breaking member and the ice, which may enhance the ice breaking action.
Fig. 1 illustrates a ship 10 wherein a first support column 18 is provided with a first ice breaking member 26. Furthermore, a second support column 20 is provided with a second ice breaking member 52. Preferably, each support column of a ship is provided with at least one ice breaking member. A single ice breaking member may extend around a support column, although it is more preferred to arrange a plurality of ice breaking members, which together extend around the support column, as indicated in Fig. 2.
Furthermore, Fig. 7 illustrates a further embodiment of the ship according to the invention comprising a guard 68 for protecting drilling equipment 70 from environmental loads, which guard 68 is located between the deck structure 16 and the float 12, wherein the guard 68 is provided with at least one ice breaking member 72. Furthermore, in Fig. 7, a ship is illustrated wherein each support column, of which only two 18, 20 are visible, is provided with substantially identical ice breaking members 26, 52, which is a preferred embodiment of the ship 10 according to the invention.
Fig. 8 illustrates another embodiment of the ship 10 of the invention, wherein the deck structure 16 has a horizontally extending second centre plane 74. Furthermore, it is realized that the ship 10 illustrated in Fig. 8 comprises ice breaking members 26 having a design which differs from the previously illustrated designs. This implementation is best described with reference to Fig. 9, illustrating a ice breaking member 26 comprising two ice breaking panels 28, 76 wherein one 28 of the ice breaking panels has a normal direction extending towards the second centre plane 74 and the second ice breaking panel 76 has a normal direction 78 extending at least partially towards the centre plane 14 of the float 12.
As described with reference to the previously illustrated embodiments of the ice breaking members, the ice breaking member 26 in Fig. 9 also comprises an enclosed volume 32, also denoted tank, and a control arrangement 34 for controlling the quantity of fluid 36 in the enclosed volume. The control arrangement 34 illustrated in Fig. 9 comprises a fluid opening 56 to the ambient environment, air flow means 58 and an air pipe 60 having a valve 62, which is a preferred embodiment of the control arrangement 34, although other control arrangements 34 are plausible.
One advantage of the ice breaking member 26 illustrated in Fig. 9 is that ice 38 may be broken both when the ice breaking member 26 moves in a direction from, i.e. out of, and towards, i.e. in to, the water 22. This advantage is illustrated in Figs. 9 and 10, wherein Fig. 9 illustrates how the ice breaking member 26 breaks ice by means of the second ice breaking panel 76 as the ice breaking means 26 is driven through the ice 38 in a direction towards the water 20 and Fig. 10 illustrates how the ice breaking member 26 breaks ice by means of the ice breaking panel 28 as the ice breaking member 26 is driven through the ice 38 in a direction from the water.
It should be realized that the present invention is not limited to the embodiments described hereinabove and illustrated in the drawings. Rather, a person skilled in the art will realize that many changes and modifications may be performed within the scope of the appended claims. For instance, the deck structure 16 on the side facing the centre plane 14 may be provided with one or several ice breaking members in areas located at a distance from support columns and guards for drilling structures.

Claims

1. A method of breaking ice (38) located on a water surface around a semi- submersible ship (10) having a weight distribution capacity, which ship comprises a float (12) having a horizontally extending centre plane (14), a deck structure (16) and at least one support column (18) extending from said float (12) to said deck structure (16), wherein, when said ship (10) floats in water (22) having a still water surface (24), said float (12) is adapted to be located at least partially beneath said still water surface (24) and said deck structure (16) is adapted to be located at least partially above said still water surface (24), wherein said ship (10) further comprises an ice breaking member (26), fixedly attached to said ship (10) in the area between said float (12) and said deck structure (16), said ice breaking member (26) comprising an ice breaking panel (28) having a normal direction (30) extending at least partially towards said still water surface (24), said ice breaking member (26) further comprising an enclosed volume (32), which is at least partially defined by said ice breaking panel (28), and a control arrangement (34) for controlling a quantity of liquid (36) in said enclosed volume (32), said ice breaking member (26) further comprises: a fluid opening (56) to the ambient environment, air flow means (58) and an air pipe (60) comprising a valve (62), wherein the method comprises the steps of: - adjusting a floating condition of said ship (10) such that at least a portion of said ice breaking member (26) is located by said ice (38), and changing the floating condition of said ship (10) by varying a quantity of liquid (36) in said enclosed volume (32), resulting in that at least a portion of said ice breaking member (26) moves through said ice (38), wherein ice (38) in the area of said ice breaking member (26) is broken c h a ra cte rize d i n t h a t the method comprises the step of decreasing said quantity of liquid (36) by closing said valve (62), and introducing air into said enclosed volume (32) by means of said air flow means (58), wherein liquid is forced to flow out of said enclosed volume (32) to the ambient environment through said fluid opening (56).
2. The method according to claim 1 , wherein the method further comprises the step of increasing said amount of liquid (36) by: opening said valve (62), whereby liquid flows into said enclosed volume (32) from the ambient environment through said fluid opening (56).
3. The method according to claim 1 or 2, wherein said change of the floating condition comprises a change of an inclination position of said ship (10).
4. The method according to any one of claims 1-3, wherein said change of the floating condition comprises a change of the draught of the ship (10).
5. The method according to any one of claims 1- 4, wherein said ship (10) comprises a plurality of said support columns (18, 20), each provided with at least one said ice breaking member (26), wherein the floating condition of the ship (10) is changed by varying the quantity of liquid (36) in several of said ice breaking members (26).
6. The method according to any one of the preceding claims, wherein said normal direction (30) of said ice breaking panel (28) extends at least partially towards said centre plane (14), wherein the method comprises breaking ice (38) in the area around said ice breaking member (26) as said ice breaking panel (28) is driven through said ice (38) in a direction towards said water (22).
7. The method according to any one of claims 1-5, wherein said deck structure (16) has a horizontally extending second centre plane (74), wherein said normal direction (30) extends at least partially towards said second centre plane (74), wherein the method comprises breaking ice (38) in the area around said ice breaking member (26) as said ice breaking panel (28) is driven through said ice (38) in a direction from said water (22).
8. The method according to claim 7, wherein said ice breaking member (26) further comprises a second ice breaking panel (76) having a second normal direction (78) extending out from said ice breaking member (26), said second normal direction (78) extending at least partially towards said centre plane (14), wherein the method comprises breaking ice (38) in the area around said ice breaking member (26) as said ice breaking panel (28) is driven through said ice (38) in a direction from said water (22) and as said second ice breaking panel (76) is driven through said ice (38) in a direction towards said water (22).
9. A semi-submersible ship (10), comprising a float (12) having a horizontally extending centre plane (14), a deck structure (16) and at least one support column
(18) extending from said float (12) to said deck structure (16), wherein, when said ship (10) floats in water (22) having a still water surface (24), said float (12) is adapted to be located at least partially beneath said still water surface (24) and said deck structure (16) is adapted to be located at least partially above said still water surface (24), said ship (10) further comprising an ice breaking member (26), fixedly attached to said ship (10) in the area between said float (12) and said deck structure (16), said ice breaking member (26) comprising an ice breaking panel (28) extending in a plane having a component which is parallel to the said centre plane (14), said ice breaking panel (28) having a normal direction (30) extending out from said ice breaking member (26), wherein said ice breaking member (26) comprises an enclosed volume (32), at least partially defined by said ice breaking panel (28), and a control arrangement (34) for controlling a quantity of liquid (36) in said enclosed volume (32) in order to change a floating condition of said ship (10), ch a racte rized i n th at said control arrangement (34) comprises: air flow means (58) for introducing air into said enclosed volume (32); an air pipe (60) comprising a valve (62), and a fluid opening (56) to the ambient environment through which fluid opening (56) fluid is allowed to flow.
10. The ship (10) according to claim 9, wherein said fluid opening (56) being located in a portion of said ice breaking member (26) located closest to said float (12).
11. The ship (10) according to claim 9 or 10, wherein said ice breaking panel (28) extends in a plane forming an angle with said centre plane (14) in the range of 80- 20°, preferably in the range of 60-30°, more preferably in the range of 50-40°.
12. The ship (10) according to any one of claims 9 - 11 , wherein said air pipe (60) comprises a first air opening (64) located in said enclosed volume (32) and a second opening (66) to the ambient air, said second air opening (66) being located at a distance from said centre plane (14) which is greater than the distance from a portion of said enclosed volume (32) located at the greatest distance from said centre plane (14).
13. The ship (10) according to claim 12, wherein said second air opening (64) is located on a side of said deck structure (16) facing away from said centre plane
(14).
14. The ship (10) according to any one of claims 9-13, wherein said normal direction (30) extends at least partially towards said centre plane (14).
15. The ship (10) according to any one of claims 9-13, wherein said deck structure (16) has a horizontally extending second centre plane (74), said normal direction (30) extending at least partially towards said second centre plane (74).
16. The ship (10) according to claim 15, wherein said ice breaking member (26) further comprises a second ice breaking panel (76) having a second normal direction extending out from said ice breaking member (26), said second normal direction (78) extending at least partially towards said centre plane (14).
17. The ship (10) according to any one of claims 9-16, wherein at least one support column (18) is provided with an ice breaking member (26).
18. The ship (10) according claim 17, wherein said ship (10) comprises a plurality of support columns (18, 20) and each support column of said ship (10) is provided with at least one ice breaking member (26).
19. The ship (10) according to any one of claims 9-18, wherein said ship (10) comprises a guard (68) for protecting drilling equipment (70) from environmental loads, such as wave loads, which guard (68) is located between said deck structure (16) and said float (12), wherein said guard (68) is provided with at least one ice breaking member (72).
PCT/SE2007/000905 2006-10-17 2007-10-16 A method of breaking ice located on a water surface around a semisubmersible ship and a semisubmersible ship WO2008048164A1 (en)

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WO2010102642A1 (en) 2009-03-10 2010-09-16 Wärtsilä Ship Design Germany GmbH Ice-breaking system for floating bodies
RU2443596C1 (en) * 2011-01-12 2012-02-27 Открытое акционерное общество "Центр технологии судостроения и судоремонта" (ОАО "ЦТСС") Semisubmersible ice breaker
US8523483B2 (en) 2010-02-03 2013-09-03 Exxonmobil Upstream Research Company Ice break-up using artificially generated waves
CN110468774A (en) * 2019-08-20 2019-11-19 中国水利水电科学研究院 A kind of ice water two-phase flow canal for water conveyance gate section ice berg control method
CN110920816A (en) * 2018-09-19 2020-03-27 哈尔滨工业大学 A new type of floating ice-resistant platform
RU2731137C1 (en) * 2019-05-29 2020-08-31 Федеральное государственное казенное военное образовательное учреждение высшего образования "Военный учебно-научный центр Военно-Морского Флота "Военно-морская академия им. Адмирала Флота Советского Союза Н.Г. Кузнецова" Floating pier
CN114455011A (en) * 2022-01-11 2022-05-10 江苏科技大学 A ship anti-rolling auxiliary ice breaking device based on Magnus principle

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WO2010102642A1 (en) 2009-03-10 2010-09-16 Wärtsilä Ship Design Germany GmbH Ice-breaking system for floating bodies
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RU2443596C1 (en) * 2011-01-12 2012-02-27 Открытое акционерное общество "Центр технологии судостроения и судоремонта" (ОАО "ЦТСС") Semisubmersible ice breaker
CN110920816A (en) * 2018-09-19 2020-03-27 哈尔滨工业大学 A new type of floating ice-resistant platform
RU2731137C1 (en) * 2019-05-29 2020-08-31 Федеральное государственное казенное военное образовательное учреждение высшего образования "Военный учебно-научный центр Военно-Морского Флота "Военно-морская академия им. Адмирала Флота Советского Союза Н.Г. Кузнецова" Floating pier
CN110468774A (en) * 2019-08-20 2019-11-19 中国水利水电科学研究院 A kind of ice water two-phase flow canal for water conveyance gate section ice berg control method
CN114455011A (en) * 2022-01-11 2022-05-10 江苏科技大学 A ship anti-rolling auxiliary ice breaking device based on Magnus principle
CN114455011B (en) * 2022-01-11 2023-03-14 江苏科技大学 Ship stabilization auxiliary ice breaking device based on Magnus principle

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