AU2009342041A1

AU2009342041A1 - Ice-breaking system for floating bodies

Info

Publication number: AU2009342041A1
Application number: AU2009342041A
Authority: AU
Inventors: Claudiu Nichita; Berend Pruin
Original assignee: WARTSILA SHIP DESIGN GERMANY GmbH
Current assignee: Wartsila Ship Design Germany GmbH
Priority date: 2009-03-10
Filing date: 2009-03-10
Publication date: 2011-09-08
Anticipated expiration: 2029-03-10
Also published as: WO2010102642A1; AU2009342041B2; RU2011136169A; JP2012519625A; KR20110137774A; JP5349621B2; CA2751898A1; EP2406126A1; EP2406126B1; CA2751898C; US20110315060A1; RU2483967C2; CN102333693A

Abstract

The invention relates to an ice-breaking system for floating bodies in or near ice, having a protruding stem and at least two trim tanks (10,16) for generating a stamping motion of the floating body, wherein the at least two trim tanks are connected fluidically by means of at least one trim channel (12,13) to high-power delivery devices (18,19) for the trim medium, and the trim system is designed as a closed loop.

Description

English translation of the international application as published Ice breaking system for floating body The invention relates to an ice breaking system for floating bodies according to the in troductory clause of claim 1 and to a method for position stabilisation using a corre sponding system according to claim 12. Ice breaking systems for floating bodies or ships are known. JP 59 179493 A discloses a system and a method wherein ballast tanks, particularly in the keel region of the ship bottom, are used in order to pump over ballast water from starboard to port and in versely so as to thereby achieve a heeling movement of the ship. Due to this weight displacement the ice can then be broken, supported by the lateral bulb formations in the bow region. A system working in a different way is known from US 3 939 789. Corresponding to this document a drillship operating in ice is equipped in the bow region with a floodable chamber. Furthermore a bow projecting in a flat manner over an ice sheet is provided. This front flooding or trimming chamber can be rapidly flooded due to relatively large openings in the bottom and side region so that sinking of the bow in relation to the nor mal waterline takes place and in this way the ice present below the bow is broken. By introducing compressed air into this chamber the trimming chamber is blown out again. A division of the trimming chamber is provided so that heeling of the bow and ship to wards port and starboard can be brought about. However, there is a risk in this design of the ship of chunks of ice being brought into the chamber during flooding which may block the corresponding openings during blowing out. Another system according to US 3 850 125 shows, with a drillship operating in ice, a spur-like bow and to the front and to the rear a respective chamber in the bottom region of the ship, which chamber can be flooded or blown out. In this way it is possible to rai se and lower the bow with an ice breaking effect.

-2 The disadvantages hereby lie also in the risk of the chambers icing up and a relatively complex structure of the compressed air means for blowing out the corresponding tanks. A floating body with a drill tower is described in US 3 872 814. The drill tower is hereby located on a floating semi-submersible rig with two lateral tubular floating bodies. These floating bodies are equipped to the rear and to the front with flooding areas. It is hereby possible to bring about, by flooding the front chamber, a sinking and at the same time an ice breaking effect against an ice sheet or drift ice. This is further favoured through periodic blowing out of the front chamber and flooding of the rear chamber. A heeling movement of the drilling rig can also be controlled with this semi-submersible rig. How ever, construction of the required compressed air systems necessitating relatively high resources and the risk of icing up of the flood chambers are also present here. A further embodiment with ice breaking effect is disclosed by JP 58 224887, in which a solid ballast weight can be drawn from the front to the rear in the keel region in order to hereby bring about a pitching of the ship with the bow against an ice sheet and thereby to exert an ice breaking function. In order to also facilitate lateral movements of a ship, for example according to DE 42 08 682 B4 an ice breaker is equipped both with jet propulsions and with rotatable pro pulsion units so that lateral movements are also facilitated. However, the known systems predominantly have the disadvantages that they are for med too inefficiently and that there is a high risk of icing up of the trimming tanks and that the blowing-out of the chambers and the weight displacement is carried out too slowly in most cases. It is thus an object of the invention to overcome the aforementioned disadvantages and in particular to create an ice breaking system for floating bodies in ice or in case of ice, in particular for drillships and research ships or platforms, in ice fields, pack ice or drift ice and the like, which reliably facilitates stationary positioning of a ship body or ship over a point on the seabed and to indicate a corresponding method for stationary posi tioning.

-3 This object is achieved in a system according to claim 1 through the features of the claim and through a method with the features of claim 12. Due to the increasing importance of the arctic oceans having regard to exploration for economically accessible oil fields and other raw materials and minerals, research ships, drillships and floating platforms which can be held stationary are increasingly necessary which in spite of the ocean current and drifting ice sheets must maintain their position as intended above the seabed in a stationary manner. The inventive system and the method thus consider these requirements. An essential core thought is thereby to provide in the bow or front region of the ship body a front trimming tank which is provided as far forward as possible and as high as possible at a distance from the keel line. In contrast herewith, a second trimming tank is provided in the rear region according to the distance and height, whereby both trimming tanks are connected to each other in terms of flow by means of at least one trimming channel. In case of one trimming channel the latter extends centrally in the longitudinal direction of the keel line. The design with two trimming channels which are placed in opposing side regions of the floating body or ship is particularly advantageous. Due to the preferred arrangement of the front and rear trimming tank above the water line a closed system is realised together with the trimming channels. The trimming tanks can, however, also be arranged as desired corresponding functionally to the ship. An anti-frost arrangement is hereby to be considered, particularly having regard to energy saving. As the system must also be fully functioning at relatively low arctic outside tem peratures, also at under -35"C, a trimming fluid, in particular water with a high salt con tent or with additives which considerably reduce the freezing point of the trimming me dium is used. The tanks and trimming channels are outwardly protected where possible against icing by cofferdams. In order to protect against icing of the tanks and / or trim ming channels heating of these installations can also be carried out as required. In arctic ocean regions in which a ship or a floating platform is to be positioned exten sively stationarily over a drill hole there is the problem - in case of more or less closed ice covering or a drift of pack ice - that the ship which is to be held stationary would drift -4 with the ice. Drift speeds of approximately 0.5 kn (knots) or less can thus arise from slowly changing directions. The ship must therefore be able to position itself in such situations dynamically, possibly at an angle or even transversely to the drift direction of the ice or the ocean current, for example over the corresponding sea position. Such a ship must therefore have an ice breaking system with the features set out in claim 1. According to the method it is provided for position stabilisation of such a ship body in ice or in case of ice, particularly using a corresponding ice breaking system according to claim 1, that on the one hand the drift of the ice and / or the ocean current is / are de termined. It is provided that in the presence of an ice drift the ship body is designed and manoeuvred so that in particular its front region points against the drift direction of the ice or the ocean current and the ice breaking system of the ship body is set in operation. In dependence upon the equipping of the ship body with corresponding underwater drive units, which can be designed for example as propulsion units rotatable by 360*and / or jet propulsions in the bow or stern, a ship equipped in this way can be held ap proximately diagonally or even transversely to the drift direction of the ice or the ocean current stationarily above the seabed. The ice breaking systems can hereby also sup port the stationary positioning of the ship body in case of ice through the production of heeling movements and / or pitching movements. In this way a relative movement of the ship body in the magnitude of the drift speed or the ocean current against the drift direction of the ice is produced so that the ship body or the ship can be held stationary for example over a seabed point, for example a drill hole. The position of the floating body itself is therefore determined for example by means of GPS or other positioning means and on the basis of the drift speed and drift direction of the ice ascertained the ship is orientated with its ice breaking function so that on the bow and / or stern side the re-trimming of the trimming medium into the front and rear tank produces the pitching, ice breaking function. On the other hand the orientation of the ship with the necessary relative speed contrary to the drift speed can be produced -5 through bow and / or stern jet propulsions possibly in combination with electromechani cal or diesel mechanical propulsion units so that the ship is held stationary over a drill hole. The propulsion units can be arranged in a pod-like manner on the ship bottom or be integrated into the hull of the ship body. The ice breaking function of the ship and the re-trimming of the corresponding medium in and to the trimming tanks are usefully carried out with a frequency which is adapted to the drift speed of the ice and thereby achieves an efficient ice breaking effect. As an improved ice breaking effect is also achieved through heeling movements of the ship, lateral trimming tanks are also provided in the region of the side walls, in particular above the water line, so that heeling movements can be produced through re-trimming thereof. The lateral trimming tanks are usefully arranged in pairs and opposite the ship's centre line. Having regard to an improvement of the rolling and pitching movements of the ship a plurality of lateral trimming tanks are preferably provided in pairs, whereby they are then arranged distributed in the longitudinal direction of the ship. The ice breaking function in the sense of trimming - ice breaking can be further im proved in that the pitching or rolling movements of the ship through the re-trimming into the tanks from front to rear and inversely can be produced in combination with the re trimming processes in the lateral trimming tanks and a resulting heeling movement. As re-trimming of the trimming medium is to be achieved in the closed system from the rear to the front trimming tank in as short a time as possible on the one hand large pipe cross-sections are provided in the trimming channels, for example of between 1 to 4 m in diameter, and high power fluid conveying means, for example as hydro-mechanical pumping means, are integrated in the closed trimming system. The corresponding fluid conveying means can provide for example conveying rates which allow in joint operation the pumping over of 500 to 1000 t trimming medium from the rear to the front in 10 to 30 s. For re-trimming for example from the front trimming tank into the rear trimming tank, however, the kinetic energy of the oscillating water mass during re-trimming is also used as a supplement to the high conveying rate of the conveying means. In this respect so to speak the rear vibrating water mass is also used to pump over the trimming medium -6 in order to be able to re-trim the trimming medium even more quickly for example from the front trimming tank into the rear trimming tank. The trimming channels are preferably brought as far as the corresponding conveying means with full volume in the pipes so that immediately the whole flow volume is avail able with a re-trimming process. This system can be supplemented by corresponding retention or non-return means which can in particular be operated and switched bi-directionally. In dependence upon the trimming medium used the fluid conveying means can also be designed to work hydraulically or pneumatically. In order to achieve a best possible pitching effect of the ship to break the ice it is prefer able to arrange the front and rear trimming tank with a height distance which is as great as possible from the keel line or bottom line of the floating body. The front and rear trimming tank are thus offset extremely far to the front and rear and provided as far as possible at the height of the main deck. In order to protect and pre vent freezing of the trimming medium the tanks and the trimming channels are prefera bly secured outwardly behind cofferdams. It is also possible to equip the front and rear trimming tanks with sub-divisions, in par ticular in the plane of the ship's centre line, whereby weight loads can also be produced alternately to the sides of the ship and the heeling movements for lateral ice breaking can thus be improved. Having regard to the production of pitching or rolling movements of the floating body it is possible to also provide only one, in particular a front trimming tank. This individual trimming tank can be flooded with existing drawn in seawater and be blown out for emptying. The individual trimming tank can, however, also be connected with lateral intermediate tanks to form a closed system so that the trimming medium can be pumped over, but remaining moreover in the trimming system.

-7 The number and arrangement of the trimming tanks, in particular for producing the pitching of the ship, is arranged and designed in the overall function with the trimming channels in such a way that the largest possible trim moments can be produced in the ship in relatively short time intervals. By way of a supplement to the preferred closed trimming system it is useful having re gard to different fields of application of such a ship to also realise, alternatively or in combination with the closed trimming system, an outwardly open trimming system. It is thus desirable also having regard to repair to be able to connect in particular the front and rear trimming tank via fluid lines outwardly to the seawater in order to thereby be able to realise auxiliarily or alternatively a trimming process. The manoeuvrability of the ship is further improved in that additionally to the main drives further direct or indirect drive means, in particular bow and stern jet propulsions, are present, possibly in combination with for example electromechanical propulsion units, whereby the latter mostly comprise rotation regions of 0 to 3600 in pod-like suspen sions. Precisely this drive combination allows a corresponding floating body or a ship to also be held, in case of drift and ocean current, stationarily over a drill hole or a defined posi tion on the seabed, in particular through computer control. The trimming system described within the scope of this invention is advantageously de signed to be computer controlled and can be used not only in ice-covered water but also with an open water area. The trimming processes usually take place fully automatically whereby a semi-automatic function is also conceivable. The computer controlled trim ming allows a plurality of trimming processes and adjustments. Both rolling and pitching movements as well as heeling movements of the floating body can thus be controlled. It is also possible to realise the periodic frequency in dependence upon predefined angles to be achieved during pitching processes or heeling processes or also a combination thereof. As there is a need for re-trimming processes which are as rapid as possible and this is to be realised in adaptation to the required frequency for the ship movements, fluid con- -8 veying means are required which facilitate a flow speed in the trimming channels with up to approx. 8 m/s. In comparison with this, pumping-over processes take place in ballast water or liquids at approximately 3 m/s. Pneumatic drives, for example blower fan units, can be used as fluid conveying means which have their threshold at approximately 10 m / head of water. Centrifugal pumps are already more advantageous in contrast therewith but wherein the control should be even quicker in the opposite direction of effect. Propeller drives and impeller drive systems have proved to be particularly suitable for the rapid re-trimming processes. The system for position stabilisation is therefore to be adapted on the one hand in rela tion to the synchronisation with the drift speed of the ice and on the other hand in rela tion to the pitching and rolling frequency of the ship having regard to the ice breaking function. In order to improve the ice breaking function the ship hull is also to be de signed to be projecting far out in particular at the bow and stern end. This is obviously supplemented for the whole ship hull through the necessary design of the ship walls and the ship bottom for the corresponding ice class. An improvement of the ice breaking effect in heeling movements is achieved through projection of the ship side walls. Having regard to the ice breaking function maximum trimming and heeling angles can also be predefined which should be considered in the re-trimming process for the rolling and heeling of the ship. In order to improve the re-trimming process having regard to time the trimming channels should constantly be filled with trimming medium at least as far as the feed pumps and the opposing empty trimming tank should have no remaining fluid. During the pumping over process it is to be ensured in particular that no air reaches inside the pumps in or der to avoid damage through cavitation.

-9 A re-trimming process can be started in this way with full volume available without delay and with corresponding diameter dimensioning of the trimming channels can also be concluded with a re-trimming volume of 500 to 1000 t between 10 and 20 s. The invention is explained in greater detail below by reference to schematic representa tions of two embodiments. The drawings show: Fig. 1 a sectional illustration with a top view from above of a ship equipped with an ice breaking system approximately at the height of the main deck, wherein a front, a rear and two lateral trimming tanks with the connecting trimming channels are shown with hatching; Fig. 2 a vertical section through the ship according to Fig. 1 along the starboard side trimming channel with sectional illustration in the front and rear trimming tank; Fig. 3 a vertical section approximately at the height of the intersection line 3 - 3 accord ing to Fig. 1; Fig. 4 a vertical cross-section approximately at the height of the intersection line 4 - 4 according to Fig. 1 and Fig. 5 a schematic illustration of a bow region of a ship with ice breaking function and pitching movement of the ship with ice breaking function shown through three line pat terns. Fig. 1 shows a horizontal section of a ship 1 approximately at the height of the main deck with the essential component groups of the trimming system. In the bow region 2 a front trimming tank 10 and in the stern region 3 a rear trimming tank 16 are shown with hatching. The trimming tanks 10, 16 are arranged as far as pos sible in a most frontal position or respectively in an extremely rear position of the ship. As shown in section in Fig. 2 the trimming tanks 10, 16 are arranged with as large as possible distance from the keel line 4 or the ship bottom 7. Due to this extreme ar rangement above the normal water line the force moments acting on the ice sheet are considerably improved.

-10 In the example the trimming tanks 10, 16 are connected in terms of flow with two trim ming channels offset in the outer region of the ship. The trimming channels 12, 13 lie below the lower level of the trimming tanks 10, 16 but in the normal case still above the water line. Feed pumps 18, 19 as high power pumps are connected in terms of effect with the trimming channels 12, 13 and the trimming medium located therein. It is also possible to arrange further feed pumps, similarly to in Fig. 1, offset to the rear additionally on the trimming channels. In order to produce a heeling movement of the ship lateral trimming tanks 21 and 22 are provided on both sides. These lateral trimming tanks 21, 22, are located very deep in the ship, as shown in Fig. 2, particularly in the bottom region of the ship. As shown in Fig. 2, the bow 2 is formed as a flat bow. This also applies to the stern 3 which has a very flat region. The bow region can also be designed in the manner of a spoon bow. The flat contour to the front and to the rear can also be realised with a suffi ciently projecting stem and stern post in order to be able to exert a good ice breaking function. In the view of the starboard side according to Fig. 2 a drive screw 31 is shown sche matically with shaft bearing 32 and drive unit 33. In the vertical sectional representation according to Fig. 3, which shows a section ac cording to 3-3 according to Fig. 1, the trimming channels 12, 13 are provided very far below in the bottom region of the ship. The shaft bearings 32 and 35 are shown project ing downwardly. The lateral side walls of the ship 1 are formed as projecting side walls 24, 25 so that in case of heeling movements an improvement in the ice breaking function is present. In the sectional illustration according to Fig. 4 along the intersection line 4-4 it is shown schematically that the trimming channels 12 or 13 go into the lateral connection boxes of the rear trimming tanks 16 and form approximately an L shape in section.

- 11 The trimming channels 12, 13 can also comprise a circular diameter having regard to the feed pumps 18, 19, whereby this diameter can amount for example to between 1 m and 4 m. Having regard to the outward protection the trimming channels and trimming tanks are additionally protected through externally lying cofferdams. The schematic illustration according to Fig. 5 shows a bow region 2 of the ship 1 and the ice sheet 41 drifting against the bow incline 38. Due to the pitching movement of the ship through the re-trimming effect into the front and rear trimming tank the ice breaking effect is achieved through the upward and downward movement of the bow 2 so that the ice sheet 41 is broken up into smaller ice sheet portions 42. A similar effect is also shown by the heeling movement to the sides with the supporting effect of the projecting lateral side walls 24, 25. The ice breaking system and the corresponding method thus allow floating bodies or ships to also be held stationary in the ice of the arctic sea up to certain ice thicknesses over a point on the seabed, for example for drilling purposes.

Claims

1. Ice breaking system for floating bodies (1) in ice or in case of ice, in particular for drillships and research ships or platforms, having at least one front ship body region or a bow region (2) projecting over the water area and an ice sheet region, having at least one trimming tank (10) provided in the front ship body region or bow re gion (2), and having a means (18, 19) for filling the trimming tank (10) with fluid and emptying it, in particular with water, to increase the weight with filled trimming tank and to reduce the weight with emptied trimming tank, for producing at least an ice breaking, pitching mo vement of the front ship body region or bow region (2) relative to the ice sheet, characterised in that trimming tanks (10, 16) are provided to the front and rear of the ship body (1) which are loaded and unloaded in an opposing manner periodically in terms of weight to produce an ice breaking, pitching movement, at least one trimming channel (12, 13) connects the front and rear trimming tank (10, 16) in terms of flow, at least one fluid conveying means (18, 19) is provided in terms of flow between the trimming tanks (10, 16) and the trimming system has a closed design.

2. System according to claim 1, characterised in that in case of one trimming channel (18) this is arranged centrally, in particular mid-ship (5), and in case of two trimming channels (12, 13) these are provided in particular in the region of opposing floating body or ship sides. - 13

3. System according to claim 1 or 2, characterised in that the floating body (1) is formed with lateral heeling tanks (21, 22), with at least one pair of opposing lateral heeling tanks or with a plurality of pairs which, distributed in the lon gitudinal direction of the ship, are arranged also for trimming, and in particular projecting side walls (24, 25) are provided in the region of the water line or somewhat above the water line.

4. System according to one of the claims 1 to 3, characterised in that the fluid conveying means (18, 19) are designed hydro-mechanically, hydraulically or pneumatically.

5. System according to one of the claims 1 to 4, characterised in that at least the front and rear trimming tanks (10, 16) are provided offset as far as possible to the front or rear in the end regions of the floating body (1).

6. System according to one of the claims 1 to 5, characterised in that the front and / or rear trimming tank (10, 16) is / are provided with sub-divisions and can also be operated as lateral trimming tanks to produce a heeling movement of the ship body (1). - 14

7. System according to one of the claims 1 to 6, characterised in that the closed trimming system (10, 16, 12, 13) comprises water with a high salt content or with additives for reducing the freezing point.

8. System according to one of the claims 1 to 7, characterised in that the fluid conveying means (18, 19) are designed, in particular with hydro-mechanical design, for high conveying rates of the trimming medium, in particular in the range of from 500 tto 1000t in 10 to 30 s.

9. System according to one of the claims 1 to 8, characterised in that means for position stabilisation of the floating body (1) and direct or indirect drive means (31) are provided for manoeuvring the ship body (1), in particular in all directions.

10. System according to one of the claims 1 to 9, characterised in that to the rear an adequately projecting stern post (3) is provided which projects over the water line and in case of an existing ice sheet over this.

11. System according to one of the claims 1 to 10, characterised in that the means for position stabilisation of the floating body (1) are designed in order to de tect a drift of the ice and / or the ocean current, and to control an orientation and counter movement of the ship body (1) against the drift. -15

12. Method for position stabilisation of a floating body (1) or ship (1) in ice or in case of ice, in particular using a system according to one of the claims 1 to 11, wherein the drift of the ice or the ocean current is determined, an orientation of the floating body (1) or ship (1), particularly with its front region (2), is carried out against the drift direction of the ice or the ocean current, an ice breaking system (10, 16, 18, 19, 12, 13) of the floating body (1) or ship (1) is set in operation, and a dynamic, relative movement of the floating body (1) or ship (1) is carried out in the magnitude of the drift speed against the drift direction of the ice or the ocean current.

13. Method according to claim 12, characterised in that the ice breaking system is operated with a frequency which is adapted for the efficient ice breaking function to the drift speed of the ice.