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Title:
DEVICE FOR A SHIP
Document Type and Number:
WIPO Patent Application WO/2014/123464
Kind Code:
A1
Abstract:
The present invention refers to a device (1) for a ship (2) arranged to be used for drilling activities at ocean and the ship (2) has at least an ice-breaking activity and is equipped with several rotatable thrusters (3). According to the invention the thrusters (3), being arranged on one hand to get away with eventual ice (4) at dynamically positioning of the ship (2) and on the other hand at an ice-breaking activity in desired directions (15, 16) to get away with loose broken ice (7) in a direction away from the ship (2), are rotatable carried and arranged to bear to a stop face (8).

Inventors:
JOHANSSON BENGT M (CA)
Application Number:
SE2013/051630
Publication Date:
August 14, 2014
Filing Date:
December 30, 2013
Export Citation:
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Assignee:
STENA REDERI AB (SE)
International Classes:
B63B35/08; B63H5/125
Domestic Patent References:
WO2008140654A12008-11-20
WO2010103170A22010-09-16
Foreign References:
US4860679A1989-08-29
US5036781A1991-08-06
Attorney, Agent or Firm:
CEGUMARK AB (S- Göteborg, SE)
Download PDF:
Claims:
CLAIMS

1. A device (1 ) for a ship (2) arranged to be used for drilling activities at ocean and the ship (2) has at least an ice-breaking activity and is equipped with several rotatable thrusters (3), said thrusters (3) are rotatably carried and are arranged on one hand to get away with eventual ice (4) at dynamically positioning of the ship (2) and on the other hand at an ice-breaking activity in desired directions (5, 6) to get away with loose broken ice (7) in a direction away from the ship (2), characterized in that the thrusters (3) directly or indirectly are carried through a frame on an inclined bottom hull part (14) having an inclination of between 15 and 20 degrees, with respect to the water line (15) of the ship (2), the thrusters (3) being arranged for action in the direction obliquely up towards the water surface, in that each one of the thrusters (3) has a rear part (16) protruding mainly in the horizontal direction and arranged to bear to a stop face (8) at the actual thrusters end position, and in that remote controlled locking means (10) are arranged for said thrusters (3) for their locking in a desired locked end position.

2. A device according to claim 1 , characterized in that the thrusters (3) are carried on the hull (1 1 ) directed to act obliquely upwards (12) and out from the length centre line (13) of the hull.

3. A device according to claim 1 , characterized in that the bear part (16A) of the end part (16) and the stop face (17) have congruent shapes, preferably a straight inclined surface (18, 19).

4. A device according to any preceding claim, characterized in that the locking means (10) are in form of a displaceably activated rod co-operating with the projection part (16) of the thrusters (3) and with the stop face (17) to prevent an overloading of the rotation bearing of the thrusters belonging thereto.

5. A device according to any preceding claim, characterized in that the thrusters (3) being rotatable about an axis, preferably about 360 degrees, are arranged along the length of the ship at other sides of the centre (13) of the ship and they are even located, e.g. as the series 4, 6, 8, 10, 12 and so on, or in the series 4, 8, 12 and so on in pairs on each side of the centre (13) of the ship, preferably in front of each other.

6. A device according to any preceding claim, characterized in that the thrusters (3) are symmetrically distributed lengthwise (5) as well as in sideway (6) under a bottom hull part (11 ).

7. A device according to claim 1 , characterized in that the ship (2) has a pointed wedge shaped stem (23) and stern (24). 8. A device according to claim , characterized in that thrusters (3) are carried at each side (A, B) about a vertically downwards directed (21 ) protruding, centred underlying longitudinal thickening (22) on the hull (1 ) of the ship.

9. A device according to any preceding claim, characterized in that in front of the thrusters (3) there is a protection (25) against ice.

Description:
Device for a ship

The present invention refers to a device for ships arranged to be used for drilling activities at ocean and the ship has at least an ice-breaking activity and is equipped with several rotatable thrusters, said thrusters are rotatably carried and are arranged on one hand to get away with eventual ice at dynamically positioning of the ship and on the other hand at an ice-breaking activity in desired directions to get away with loose broken ice in a direction away from the ship.

0 WO-A1 -2008/140 654 includes azimuthing propulsion devices and as examples thrusters (216a) are shown in the drawings, e.g. in Figs. 2A through 2E. For instance according to Wikipedia the use of "Azimuth thrusters" involves a group of propellers carried by holders rotatable in a desired horizontal direction making the use of a rudder unnecessary. Thus it is not the question of5 something directing a water jet obliquely upwards to get away with the ice.

US 4 860 679 (SE 465 421 ) includes a ship with a rudder (15, 15a, 15b) rotatably carried about a vertical axis (19) and in the end position of its rotation being arranged to co-operate with end stops (20, 22) to prevent ice from arriving at the propellers (13) inside thereof. There is no teaching of the o document which suggests that end stops also would to be used for stops of propellers.

US 5 036 781 refers to a construction being used to get away with ice from the bottom and/or sides of a ship by air exhaustion from a fan device (7) onboard by having the propeller flow abducted by a rudder (10) according to 5 Fig. 2 or by rotation of propellers (3) about inclined axes and to direct the

propellers obliquely upwards according to Fig. 3. In the case known per se it is the permanent propellers (3) of the ship being tilted.

Therefore the main purpose of the present invention is in first hand to solve the problem of to make use of the ship with said thrusters also in hard ice o without damaging the thrusters or bringing them out of the set positions, e.g. due to ice actions. This purpose is obtained by a device according to the present invention mainly characterized in that the thrusters directly or indirectly are carried through a frame on an inclined bottom hull part having an inclination of between 15 and 20 degrees, with respect to the water line of the ship, the 5 thrusters being arranged for action in the direction obliquely up towards the water surface, in that each one of the thrusters has a rear part protruding mainly in the horizontal direction and arranged to bear to a stop face at the actual thrusters end position, and in that remote controlled locking means are arranged for said thrusters for their locking in desired locked end position.0 The invention is described below as a preferred embodiment, whereby reference is made to the drawings enclosed, where

Fig. 1 shows a cross-section of a preferred hull design,

Fig. 2 shows schematically a preferred design of the stem of the craft,

Figs. 3 - 4 show a cross-section and a view from above respectively of5 a craft provided with a moon pool (an opening with a shaft belonging thereto in the bottom of the ship),

Figs. 5 - 6 show a cross-section and a view from above respectively of a craft provided with wing shaped diverters in front of the thrusters,

Fig. 7 shows a cross-section of a craft having thrusters mounted on an o inclined part of the hull,

Fig. 8 shows a view from above of one end of the craft and the thrusters mounted thereto,

Figs. 9 - 10 show a front view and a view from above respectively of the craft with the mounted thrusters rotated with respect to stop faces,

5 Figs. 11 - 2 show views from above of the craft having the thrusters rotated for ice breaking of thin ice at a high speed and for ice breaking of thicker ice at a lower speed respectively,

Figs. 13 - 14 show views from above of the craft having the thrusters rotated in different positions,

o Figs. 15 - 16 show a front view and a view from side respectively of a thruster, Figs. 17 and 18 show a stop face co-operating with a rotated thruster, and

Fig. 19 shows a cross-section view of a stop face and a thruster in locked position.

Background

Drilling has been performed by floating units in moving ice at least since the 1970's when Dome Petroleum started extensive exploratory operations in the Canadian Beaufort Sea. By early 1980's the fleet consisted of four ice strengthened drill ships, two icebreakers capable of breaking about 1.5 m thick ice and four smaller icebreakers capable of breaking about 0.6 m thick ice in the continuous mode of operation. The drill ships had a hull form intended for operation in open water but they were still capable of staying on location until early December when the ice reached a thickness of about 0.6 m when assisted by several icebreakers managing the incoming ice. Due to the small water depth the drill ships were anchored to the ocean floor and thus on occasion presented their maximum length towards the ice movement.

At this time Gulf Canada introduced a competing drilling fleet designed to stay on location until the end of January when the ice reaches a thickness of 1.2 m in the Beaufort Sea. The drilling unit was a round drill ship with sloping sides intended to break the ice in the downwards direction. The drill ship was assisted by four icebreakers capable of breaking about 1.5 m thick in the continuous mode of operation. The round hull form proved to be unfavorable in open water conditions, increasing down time in a sea state compared to normal drill ships. The round drill ship was anchored to the ocean floor and drilled successfully in moving ice of about 1 m thickness.

One of the Dome drill ships was fitted with a powerful air bubbling system along the sides of the ship which created a strong surface current directed away from the parallel mid body and thus made in easier for the broken ice to get around the unit. Since the 1990's a more efficient method to reach the same result in the form of rotatable thrusters creating a strong surface current has been tested successfully on several icebreakers intended for operation in first year ice conditions.

When drilling a 400 m core close to the North Pole in about one thousand meters water depth it was proven that with sufficient icebreaking support it is possible to stay on location even in moving multi-year ice of considerable thickness.

Several dynamically positioned drill ships for operation in deep water are known, each fitted with six rotatable thrusters mounted below the bottom of the ship in order to optimize the station keeping capability of these units. One of these drill ships is provided with a hull and propulsion ice strengthening which allows it to operate virtually in any ice conditions when assisted by icebreakers. If an assisting icebreaker is able to provide an ice free

environment around this icebreaker they will be able to operate in very severe ice conditions when occasionally assisted by additional icebreakers.

The Invention

A novel hull form in combination with thrusters below the bottom of the ship that direct their propeller stream towards the ocean surface in order to keep ice from close contact with the sides of the ship establish the principal feature of this invention.

The body plan of the hull is shown in Fig. 1 which manifests that the bow and the stern are essentially identical in order to operate in opposite directions while drilling in the dynamic positioning mode. This is important when the ice movement discontinues for some period of time and, as frequently is the case, starts again in the opposite direction.

Fig. 1 displays an inclined bottom portion over the entire length of this section under which rotatable thrusters may be mounted in such a manner that their propeller stream encounters the ocean surface around the entire ship. Between the sloped bottom and some distance above the deepest operating water line the side of the ship along its entire length is sloped outwards at a large angle, in Fig. 1 shown as 45 degrees, in order to facilitate turning of the ship in heavy ice conditions. Fig. 2 indicates a fairly conventional wedge shaped and pointed bow and stern portion. This hull form is not optimal for the breaking of ice but due to the efficiency of the bottom mounted thrusters in transporting broken ice along the hull the performance of the unit in heavy ice will nevertheless be exceptional. The wedge shaped stem and stern portion is essential when staying on location as it causes the broken ice to move sideways and not downwards and under the bottom of the ship.

As the thrusters protrude below the bottom of the main hull it is possible to introduce a central wing shaped ice diverter close to the amidships portion in order to deflect broken ice away from the moon pool area, as shown in Figs. 3 and 4, without increasing the minimum water depth in which the unit is able to operate. This also makes it possible to introduce two additional wing shaped diverters at both ends of the ship in order to provide protection for the thrusters by stopping progress before riding too high up on thick multi-year ice as shown in Figs. 5 and 6. By protruding well below the bottom of the hull the three ice diverters also function as very efficient roll motion reducers in a sea state. If there is a docking facility available that has the capability to accommodate the draft including the total vertical extent of the ice diverters then these may be connected permanently to the bottom of the main hull, otherwise the ice diverters have to be connected to the hull in the floating mode in the same manner as the thrusters.

In order for the thrusters to flush the hull and surroundings equally on both sides as well as at both ends of the ship it becomes obvious that they must be located in pairs both transversely and longitudinally from which it follows that the number of thrusters must be divisible by four or in other words that their number must follow the series 4, 8, 12 and so on. In the examples used in this presentation the number of thrusters is kept constant at eight.

The body plan with the thrusters in the icebreaking mode is shown in Fig. 7 and the lines plan with the thrusters in the icebreaking mode is shown in Fig. 8. The thrusters closest to the bow are directed in or close to the longitudinal direction in order not to interfere with the thrusters closer to amidships. The central ice diverter will direct the propeller stream towards the ship's side, as indicated in Fig. 8, and thus this propeller stream will also augment the sideways transport of broken ice.

The body plan with the thrusters in the station keeping mode is shown in Fig. 9 and the lines plan with the thrusters in the station keeping mode is shown in Fig. 10. As the thrusters are attached to the inclined bottom portion of the hull the propeller stream will meet the ocean surface some distance from the hull and thus the outward surface current so created will transport broken ice away from the hull which creates a lower concentration of broken ice at this location, reducing the ice load on the unit and at the same time make it easy to turn the ship into the direction of the incoming ice.

Fig. 11 shows the underwater hull while breaking thinner ice at high speed. Providing extra room for broken ice at the stern is not necessary at high speed operation and thus the stern propellers are turned to maximize forward thrust without their propeller streams influencing the operation of other propellers.

When operating at slow speed in heavier ice it becomes critical to provide extra room for broken ice at the stern by directing the propeller streams of the propellers close to the stern away from the ship, as shown in Fig. 12. As long as the thrusters create an unobstructed path for the broken ice to move behind the ship the forward progress will continue and may be augmented by also using the stern thrusters to create an oscillating sideways movement of the stern in order to further loosen the grip of the ice. The ice clearing action provided by the thrusters makes it impossible for the ship to become stuck in ice even if the ice is under heavy pressure.

Fig. 13 shows the ship while reducing the amount of ice in an already broken channel in order to make it possible for a wider or otherwise less capable ship to navigate in heavy ice. The same procedure may be used when assisting another drill ship to stay on location in heavy ice. This capability may prove to be essential in the unlikely event that a relief well has to be drilled in heavy ice conditions.

The principal operation of the thrusters while working in dynamic positioning mode is shown in Fig. 14. Having eight thrusters makes it possible to create the necessary transverse and longitudinal forces without having to direct the propeller streams towards the center of the ship, thus making it possible to always keep a surface current directed away from the unit.

The thrusters located at the forward end of the unit when advancing in heavy ice will come in contact with substantial pieces of ice and will thus have to be capable of dealing with considerably larger forces than those

experienced in open water operation. The nozzle makes it impossible for large pieces of ice to contact the propeller blades and thus the propeller and the gear driving the propeller have to be strengthened only in order to deal with the largest piece of ice that is able to gain entrance into the nozzle. In order to reduce the size of design ice piece and at the same time make it more difficult for a large piece of ice to block the flow of water into the nozzle a support structure in front of the nozzle as shown in Figs. 15 an 16 has been developed. Four wing shaped structures placed at 90 degree angles in front of the nozzle reduce the size of ice piece that is able to flow into the nozzle and at the same time add considerable strength to the nozzle. The almost vertical support structure is the widest, it provides passage for the driving shaft and any pipes and cables needed at the propeller hub, and is provided with a virtually vertical leading edge in order to turn sideways large pieces of ice. The three remaining support structures are provided with a backward leaning leading edge in order to push large ice pieces away from the center of the propeller. The outermost part of these three structures protrudes well in front of the nozzle in order to reduce the tendency for the ice piece to remain in front of the nozzle and thus to impede the free flow of water into the propeller.

The loads on the main thruster bearing and the turning gear caused by the nozzle coming into contact with large pieces of ice will be considerably higher than those caused by operating in water without ice being present. In order to unload the turning gear the top of the nozzle is provided with a wing shaped structure extending a considerable distance behind the nozzle as shown from the side in Fig. 16. The trailing edge of the wing shaped structure will come into contact with a stopper when the nozzle is turned in the optimum direction for ice breaking operations, see Fig. 8. These nozzle configurations are shown in more detail in Figs. 17 and 18. The turning gear presses the wing shaped structure against the stopper with the force the turning gear is designed for and the stopper is placed in a location that causes the load on the stopper to increase when large pieces of ice come in contact with the thruster configuration. The stopper resists the entire addition to the turning moment caused by contact with ice and thus the turning gear is not loaded beyond its design moment. As shown in Figs. 17 and 18 the stopper is also capable of carrying the additional longitudinal load caused by ice forces and thus the main bearing resisting longitudinal forces is not overloaded by ice contacting the thruster configuration. The distance between stopper and main bearing cannot be manufactured with as small a tolerance as the main bearing and thus it is important that contact between stopper and wing shaped structure depends on the rotation of the thruster unit, which will correct any difference in tolerances.

Ice contact with the thruster configuration will also increase the bending moment the main bearing has to carry unless mitigating measures are undertaken as shown in Fig. 19. On its own the main bearing would have to carry the entire additional moment caused by ice making contact with the thruster unit. By adding a contact point on top of the wing shaped structure above the nozzle, shown as a threaded bolt in Fig. 20, the major portion of the additional bending moment is carried by the supporting bolt while the main bearing is mainly loaded by a force pulling down and very little bending.

Depending on the detail of the design the bearing will be able to carry an ice load which is about 10 times larger than the thrust developed by the propeller when the supporting bolt is operational. It is fortunate that the propeller thrust always acts in the direction opposite to the ice load.

More in detail the present invention includes a device 1 of a ship 2 being arranged for use by drilling work at ocean, the ship 2 has at least some ice breaking capacity. The ship 2 is equipped with several rotatable thrusters 3. The thrusters 3 are on one hand arranged to divert free ice 4 in the dynamic positioning of the ship 2 and on the other hand when used as an ice breaker in desired directions 5, 6 to divert loose broken ice 7 in a direction away from the ship 2. The thrusters 3 are rotatably carried and bear to a stop face 8. The thrusters 3 are carried directly or indirectly on the hull 11 and with such direction that they act obliquely up 12 and out from the length centre line 13 of the hull. The thrusters 3 are carried on an inclined bottom hull part 14 inclined with an angle X of between 15 and 20 degrees with respect to the water line 15 of the ship. Alternatively the thrusters 3 may be arranged to be carried on a frame or just on the inclined ship hull, but in such a way that they act in a direction obliquely up towards the water surface.

Each one of the thrusters 3 has an end part 16 mainly projecting in an horizontal direction and in the end position of the thrusters belonging thereto it is arranged to bear to said stop face 8. The bear part 17 of the end part 16 and the stop face 8 have congruent shapes, preferably a straight inclined surface 18, 19.

The action of the stop face 8 is such that it also prevents overloading in an horizontal direction of the bearing by which the thrusters 3 is carried. To be possible to accumulate a moment and to prevent a vertical overloading of the thrusters developed in the thrusters 3 at a desired ice breaking position there are remote controllable means 10 for the thrusters 3 to keep them in the desired position. Preferably said means 10 are in form of an activated threaded rod at said end projection part 16 of the thrusters 3. To obtain a distinct end position for each one of the thrusters the tip of the means 10 can be received in a suitable shallow recess in the top surface of the end part 16.

The arrangement and distribution of thrusters 3 at the ship 2 has been chosen in such a way that the result will be an equal drive and equal action thereof. Therefore, there is an even number of thrusters 3 distributed at the bottom hull 11 , in view from amidships across the ship 2, along an imaginary transverse line 20. Namely the thrusters 3 in the series 4, 8, 12, etc. are distributed symmetrically lengthwise 5, 6 as well as sideways 27 under a bottom hull part 11 of the ship 2.

At the embodiment shown there are an even number of thrusters 3 carried at each side A, B about a vertically downwards directed 21 protruding, centred underlying longitudinal thickening 22, similar to a keel, on the hull 1 1 of the ship. To make ice breaking possible with the ship 2 in both the travel directions 5, 6 thereof, the ship 2 has a pointed wedge shaped stem 23 and stern 24.

With the purpose to obtain an effective protection for the thrusters 3 there is a protection 25 for ice arranged in front of the thrusters 3, viewed in the direction of travel of the ship, said protection 25 takes the first impact of ice blocks and the like.

The nature and function of the present invention ought to have been understood by that described above and by help of that shown by the drawings. By thrusters is in first hand to be understood a motor driven propeller which with or without an angle gear is connected to the ship 2 and its hull 11. Also other drive force generators than thrusters 3 shown and described above can be used, such as for instance water jets etc. The thrusters 3 are rotatable carried about a respective axis 26 extending transversely to the inclined bottom part 14 of the hull 1 1 or they are carried by a cantilever being arranged in such a way that it generates the desired flow direction obliquely up towards the water surface for the thrusters 3. Preferably the thrusters 3 are rotatable about 360 degrees before a stop position 9 is obtained between the stop face 8 and its bear part 7 and the bear part 16A of the end part 16 of the respective thrusters 3.

Of course the invention is not restricted to the embodiments described above and shown on the drawings enclosed. Modifications are possible, in particular when it comes to the nature of the different parts, or by making use of equivalent technique without departing from the scope of the invention such as it is defined by the claims.




 
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