SE1350161A1 - Boat with thrusters for ice removal - Google Patents

Abstract

The invention relates to a vessel (2) (23) which has a substantially uniform fore and stern (24) and which is arranged to be used both in certain ice-breaking operations and in stationary drilling operations, the hull (ll) of the vessel having sides (10) inclined at between 30 and 60 ° to an imaginary horizontal line (100) angle (d) up to a level exceeding that of the vessel (15). According to the invention, a plurality of thrusters (3) are distributed along and supported by the bottom of the vessel (102) so that the effective water flow (12) of said thrusters is directed at an angle (ß) (15) obliquely upwards. against the water surface surrounding the vessel (2) in water (103). (Fig. 16)

Description

The present invention relates to a vessel which has a substantially uniform fore and stern and which is arranged to be used both in certain ice-breaking operations and in stationary drilling operations and in that the hull of the vessel has sides which are inclined at an angle between 30 and 60 ° towards an imaginary horizontal line, up to a level that exceeds the ship's deepest active waterline.

When using the vessel for both a certain ice-breaking function and for stationary activities at sea, such as drilling operations, it is important to prevent broken ice and / or other by-flowing ice from entering the vessel and setting it up, but instead forcing it to move. away the ice in the direction away from the ship.

The main object of the present invention is therefore primarily to solve the above-mentioned problems.

Said object is achieved by means of a device according to the present invention which is mainly characterized in that a plurality of thrusts are distributed along and supported by the bottom of the vessel so that the effective water flow of said thrusters is directed at an angle obliquely towards the water surface surrounding the vessel in water. .

The invention is described below as a preferred embodiment, reference being made to the accompanying drawings in which Pig. Fig. 2 shows a cross-section of an example of a preferred hull shape, Fig. 2 schematically shows a preferred shape of the bow of the vessel, Fig. 3-4 shows a cross-section and a plan view, respectively, of a vessel provided with a moon pool, i.e. an opening in the bottom of the vessel with associated shaft, Fig. 5-6 shows cross-section and plan view of vessel equipped with wing-shaped protection in front of the thrusters, Fig. 7 shows cross-section of vessel with stored thrusts on the inclined part of the hull, Fig. 8 shows plan view Fig. 9-10 shows the front view and the plan view of the vessel with the thrust stored therewith rotated in relation to the stop stop, Fig. 11-12 shows plan views of the vessel with the thrusters turned for icebreaking of thin ice in high speed and for icebreaking thicker ice at lower speeds, Fig. 13-14 shows plan views of the vessel with the thrusters rotated in different positions, Fig. 15 shows a front view of a thruster and Fig. 16 shows a sectional view of ships with altars native hull shapes and storage of thrusts thereon to achieve the desired function.

Background Drilling has been performed by floating units in moving ice at least since the 1970s 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 l0 15 20 25 30 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 an- chored to the ocean floor and thus on occasion presented their maximum length towards the ice movement.

At this time Gulf Canada introduced a com- peting drilling fleet designed to stay on location until the end of January when the ice reaches a thickness of l.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 l.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 l 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 l990's a more efficient method to achieve 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 pos- 10 15 20 25 30 sible to stay on location even in moving multi-year ice of considerable thickness .

Several dynamically positioned drill ships are known for operation in deep water, 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 in virtually 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 oc- casionally 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 es- tablish the principal feature of this invention.

The body plan of the hull is shown in Fig- ure l which manifests that the bow and the stern are es- sentially identical in order to operate in opposite direc- tions 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.

Figure l 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 dis- tance above the deepest operating water line the side of the ship along its entire length is sloped outwards at a lO l5 20 25 30 large angle, in Figure l shown as 45 degrees, in order to facilitate turning of the ship in heavy ice conditions.

Figure 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 a midship portion in order to deflect broken ice away from the moon pool area, as shown in Figures 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 pro- vide protection for the thrusters by stopping progress be- fore riding too high up on thick multi-year ice as shown in Figures 5 and 6. By protruding well below the bottom of the hull the three ice diverters also function as very ef- ficient roll motion reducers in a sea state. If there is a docking facility available that has the capability to ac- commodate 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 divert- ers 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 l0 15 20 25 30 located in pairs both transversely and longitudinally from which it follows that the number of thrusters must be di- visible by four or in other words that their number must follow the series 4,8, l2 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 Figure 7 and the lines plan with the thrusters in the icebreaking mode is shown in Figure 8. The thrusters closest to the bow are directed in or close to the longitudinal direction in order not to in- terfere with the thrusters closer to midship. The central ice diverter will direct the propeller stream towards the ship's side, as indicated in Figure 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 Figure 9 and the lines plan with the thrusters in the station keeping mode is shown in Figure 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, reduc- ing 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.

Figure ll 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 l0 15 20 25 30 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 Figure l2. As long as the thrusters create an unob- structed 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.

Figure 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- ure l4. 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 sur- face current directed away from the unit. If mooring winches provided with underwater fairleads are added to the unit it will be capable of staying on location also in shallow water. If the thrusters are capable of keeping the unit on location even if one of the mooring wires should lO 15 20 25 30 fail it will be possible to operate with six mooring sys- tems. The mooring pattern with mooring lines at 90 degree angles against each other will create a system that only allows minor excursions from the desirable drilling loca- tions.

The thrusters located at the forward end of the unit when advancing in heavy ice will come in con- tact 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 driv- ing 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 diffi- cult for a large piece of ice to block the flow of water into the nozzle a support structure in front of the nozzle 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 al- most 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 virtu- ally 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 pro- trudes well in front of the nozzle in order to reduce the tendency for the ice piece to remain in front of the noz- lO 15 20 25 30 zle 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 pre-sent. 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. 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. 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 stop- per 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. 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 can not 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 toler- ances .

More particularly, the present invention comprises a vessel 2 which has a substantially uniform 23 and stern 23 and which is arranged to be used both in certain ice-breaking operations and also in stationary drilling operations. The hull 2 of the ship 2 has sides 10 which are inclined at an angle d which is between 30 and 60 ° towards an imaginary horizontal line 1, up to a level 100 which exceeds the deepest effective waterline 15 of the ship. According to the invention, a plurality of thrusters 3 distributed along and supported by the ship's hull 11 on the bottom 102 of the ship 2 so that said active water flow 12 of said thrusters is directed at an angle B obliquely up to the water surface 15 surrounding the ship 2 in the water 103.

In this case, the angle B at which the thrusters 3 effect the flow of the water in the direction 12 towards the water surface 15 is between 10 and 30 ° towards an imaginary horizontal line 104 and even more preferably between 15 and 20 °, which angle B the said lower bottom sides 14 can also lean with.

The present invention relates, as stated above, to a vessel 2 which is arranged to be used in work when drilling at sea and which also has at least some ice-breaking function. The said vessel 2 is provided with a plurality of rotatable thrusts 3. Said thrusts 3 are arranged to be able to propel away any loose ice 4 during dynamic positioning of the vessel 2 and to be able to move in the desired directions 5, 6 during ice-breaking operation. drive away broken ice 7 in the direction away from the vessel 2. In this case, said thrusts 3 are mounted rotatable and can be mounted against a stop stop 8.

The said thrusters 3 are mounted directly or indirectly on the hull 11 and are directed so as to act obliquely upwards 12 and out from the longitudinal center line of the hull 13. The thrusters 3 are then mounted either on a sloping bottom hull portion 14, which extends along substantially the entire length of the vessel. and which is inclined at an angle B between 10-30 and preferably between 15 ° and 20 °, seen towards the waterline 15 of the ship 10, or that they are supported by a bracket 105 which is arranged to provide the desired said flow direction 12 obliquely upwards towards the water surface 15 of the thrusters 3.

The said thrusters 3 each have their substantially horizontally projecting rear part 16 which are arranged to abut against said stop stop 8 in the end position of the thrust in question. The stop part 17 of the said rear part 16 and the stop stop 8 have a concave shape, preferably straight sloping surface 18, 19.

The arrangement and distribution of thrusts 3 on the vessel 2 is chosen so that the result will be an even drift and an even effect thereof. Therefore, a preferably even number of thrusts 3 are distributed on the bottom hull 11, seen from the center of the vessel across the vessel 2, along an imaginary transverse line 20, preferably in the series 4,6,8,10,12 and so on or in the series 4, 8, 12 M and so on. Furthermore, the thrusters 3 are suitably distributed in pairs symmetrically, both in longitudinal direction 5, 6 and in lateral direction 27 below a bottom hull portion 11 of the vessel 2.

In the exemplary embodiment shown, an even number of thrusters 3 are stored on each side A, B of a central longitudinal thickening 22, similar to a keel projecting in the direction vertically downwards 21, similar to a keel, on the hull sides 11 of the vessel, and with the thrusters 3 rotatable about an axis preferably about 360 °.

To enable icebreaking with the vessel 2 in its two directions of travel 5, 6, the vessel 2 has a pointed wedge-shaped 23 and stern 24.

A number of said bodies 22, 25 are placed at, and arranged to extend along, the center 13 of the ship. Of these bodies, which have a pointed shape in front of the stern and stern, a body, the central body 22, has substantially vertical side surfaces.

The essential thing is that the propeller stream 12 from the thrusters 3 is directed towards the water surface 15 at an angle ß between 10 and 30 degrees and that the ship sides higher up have an angle between 30 and 60 degrees so that it will be possible to rotate the ship in operation with dynamic positioning and to reduce the force of the ice when drilling in an anchored position.

The three bodies 22, 25 are all located along the middle 13 of the ship and functionally have in common that they are in open water, i.e. in waves, radically reduces the rolling of the ship which is very important when drilling. The central body 22 acts as an ice diverter as it shovels the broken ice sideways, both forward and aft, and thus radically reduces the risk of ice coming into contact with an existing drilling pipe connecting a drilling rig to the equipment on the sea. bottom. The bodies 25 in the stern and stern act as a stop to prevent the ship from driving too far up on perennial ice during breakage of the approach, which could cause damage to the thrusts 3.

The nature and function of the present invention should have been understood from the foregoing and with the aid of what is shown in the drawings. By thruster is meant primarily a motor-driven propeller which, with or without angular gear, is connected to the vessel 2 and its hull ll. Also propulsion generators other than thrusters 3 shown and described as above can be used, such as e.g. . water jet jets, etc. The thrusters 3 are mounted rotatably about their respective shafts 26 which extend perpendicularly from the inclined bottom portion 14 of the hull 11. Preferably, the thrusters 3 are rotatable about 360 ° before the stop position 13 is reached between the stop stop 8 and its stop part 17 and stop part on the rear part 16 of the respective thruster 3.

The invention is of course not limited to the embodiments described above and shown in the accompanying drawings. Modifications are possible, in particular as regards the nature of the various parts, or by the use of equivalent technology, without departing from the scope of the invention as defined in the claims.

Claims (10)

10 15 20 25 30 14 S283 P7SE LG / AHT PATENT CLAIMS Vessels (2) (23) which have a substantially uniform bow and stern (24) and which are arranged to be used both for certain ice-breaking operations and for stationary drilling operations and for the hull (ll) of the vessel to have sides (10) inclined at an angle (d) between 30 and 60 ° to an imaginary horizontal line (1), up to a level (100) exceeding the deepest effective waterline (15) of the ship, characterized in that a plurality of the bottom (102) (12) of the goat thrush (3) are distributed along and supported by vessels so that the effective water flow of said thrusters is directed at an angle (ß) (15) obliquely to the water surface surrounding the vessel (2). ) in water (103). Vessel according to claim 1, characterized in that the angle (B) provided by the thrusters (3) (12) is between 10 and 30 ° towards an imaginary horizontal line (104). the flow of water towards the water surface (15) Vessel according to one of the preceding claims, characterized in that the thrusters (3) are carried up (14) (105) (12) substantially close to the bottom hull of the vessel which is angled or that they are supported by a bracket which provides the said desired direction of flow to the thrusts (3). 10 15 20 25 30 15 Ship according to claim 3, wherein the thrusters (3) (14) are supported against the angled bottom hull (14) of the ship between 10 and characterized in that the bottom hull (102) has inclined bottom sides with an angle (B) 30 ° to an imaginary horizontal line (104). Vessel according to claim 4, characterized in that said inclined bottom sides (102) extend along the entire length of the vessel. Vessel according to claim 5, characterized in that said lower bottom sides (102) are inclined at an angle (ß) which is between 15 and 20 °. Vessel according to one of the preceding claims, characterized in that the thrusters (3), which are rotatable about an axis preferably about 360 °, are located along the length of the vessel on each side of the center (13) of the vessel, wherein they are placed evenly, for example in the series 4,6,8,10, l2 and so on or in the series 4, 8, 12 and so on in pairs on each side of the center of the ship (13), and preferably in the middle of each other. Vessel according to one of the preceding claims, characterized in that the upper sides of the vessel (10) are inclined at an angle (d) of between 40-50 °. Vessel according to one of the preceding claims, characterized in that a number of ice diverters (22, 25) are located at, (13). and arranged to extend along the center l6 of the ship Ship according to claim 9, characterized in that said ice diverters (22, 25) are pointed in the fore and stern and that one (22) of said ice diverters (22, 25) has substantially vertical side surfaces.