Arrangement for Ice-Breaking

The present invention concerns a device for icebreaking with icebreaking hull of ship.

BACKGROUND

A scientific treatment of icebreaking resistance was published in 1888-1889 in Great Britain by Robert Runeberg, a Finnish engineer, in Reference [Runeberg, Robert; “On Steamers for Winter Navigation and Ice-breaking” Paper No. 2371 of the Proceedings of the Institution of Civil Engineers 1888-1889]. In this reference only the resistance caused by the breaking of the ice is considered and a formula for the calculation of the relationship between the resisting force, R, and the vertical force, V, when breaking a solid ice sheet of uniform thickness is presented. Among many the formula includes the following input parameters:

f coefficient of friction
Φ angle between the mean inclination of the buttock lines and the water line
β angle between water line and mean inclination of cross sections taken perpendicular to buttock lines

Commenting on how these angles influence the efficiency of icebreaking Runeberg states the following on top of page 293 in said Reference [Runeberg, Robert: “On Steamers for Winter Navigation and Ice-breaking” Paper No. 2371 of the Proceedings of the Institution of Civil Engineers 1888-1889]:

“Turning attention to the design of the vessel, it will be inferred from the formula for V, that in order to increase the ice-breaking capacity; the angles Φ and β should be made as small as possible.” In other words the inclination of the buttocks and the frames against the water line should be as small as possible in order to maximize icebreaking efficiency.

This scientific illumination has been widely used on icebreakers built to break level ice on inland waterways. The most extreme examples have a frame angle β of zero degrees, which results in a totally flat landing craft bow, in combination with a buttock angle Φ of less than 10 degrees.

Icebreakers intended mainly for service in open sea, where heavy ridges are present, have experienced a different evolutionary process. The first European icebreaker intended for operation in open sea was designed and built in Sweden for the Finnish government in 1890 and was given the name Murtaja, which in Finnish means Breaker. This design by C. A. Lindvall had a length of 47.5 m, a beam of 10.9 m, a draft of 6.7 m and a displacement of 930 tonnes. It had one propeller and a power of 1 MW. The lines and body plan of this ship are shown in Reference [Runeberg, Robert: “Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900], and indicate a spoon shaped bow with an average buttock angle of about 40 degrees and an average frame angle of about 60 degrees. The water line was rather blunt with an opening angle of about 48 degrees at the stem.

In heavy pack ice the performance of Murtaja was highly unsatisfactory because the blunt bow pushed broken ice in front of itself and the ship got so badly stuck that dynamite, saws, axes and ice anchors had to be used to free the ship from the grip of the ice. This extremely negative experience resulted in the conclusion that an icebreaker intended for operation in open sea must be equipped with a relatively sharp wedge shaped bow in order to avoid pushing ice in front of itself.

In 1893 an icebreaking ferry, the Saint Marie, was built in Detroit, Mich. to the design of Frank E. Kirby. It was fitted with two propellers, one at the stern with a power of 1.4 MW and one at the bow with a power of 1.14 MW for a total power of 2.54 MW. The lines and body plan of this ship are shown in Reference [Runeberg, Robert: “Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900], and indicate almost identical rather sharp wedge forms at the bow and stern, which is to be expected in order to accommodate the propellers. According to reports reaching Finland this ferry operated with great success in heavy pack ice by alternatively running the bow propeller full astern and full ahead when making slow progress. In 1895 a Finnish engineer, Konstantin Jansson, was sent to document the operation of these ferries and the following year a Finnish sea captain, L. Melán, was also sent to the Great Lakes in order to assert the operational efficiency of the Kirby design. Jansson and Melán both recommended that the next Finnish icebreaker should be fitted with two propellers, one at each end, even if the cost of the ship should increase, Reference [Ramsay, Henrik: “I kamp med Östersjöns isar” Struggling with the Ice in the Baltic Sea”, (in Swedish), Helsinki 1947].

The second Finnish icebreaker was built in Newcastle upon Tyne 1n 1898 and given the name Sampo, with a length of 61.6 m, a beam of 13.1 m, a draft of 5.56 m and a displacement of 2,050 tonnes. It was fitted with two propellers, one at the stern with a power of 1 MW and one at the bow with a power of 0.88 MW for a total power of 1.88 MW. The lines and body plan of this ship are shown in said Reference [“Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900] and are very much in accordance with Kirby's design for the Great Lakes. Obviously the operators were satisfied with a wedge shaped hull form provided with propellers at the bow as well as the stern as this design did not change materially until the 1980's for icebreakers intended for operation in the northern portion of the Baltic Sea.

The evolution of icebreakers intended for polar regions has been somewhat different from that of icebreakers intended for more temperate climates. The first icebreaker to be tested in the Arctic was the Russian icebreaker Ermak sponsored by Admiral Makaroff and built 1898 in Newcastle upon Tyne. In said Reference [“Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900] this is described as follows:

“In February, 1983, the author read a paper before the Russian Imperial Technical Society on “The Possibility of Winter Navigation to St. Petersburg.” In this Paper the conclusion was arrived at that winter navigation to St. Petersburg should not be impossible. It is to Admiral Makaroff that the honor is due of having put this suggestion to a practical test. The Minister of Finance having found the money, Admiral Makaroff ordered the icebreaker from Messrs. Armstrong, Whitworth & Company, and on the 16^thMar. 1899, she arrived at Kronstadt, met by an enthusiastic crowd on the ice. The lines of this vessel are very similar those of the Sampo, though the Ermak is much larger.” Ermak's length was 97.5 m, beam 21.6 m, draft 8.54 m and displacement 7,875 tonnes. Initially she was fitted with four propellers, each of 1.56 MW for a total power of 6.24 MW. One propeller was fitted at the bow while the three others with a single centerline rudder were located at the stern. In said Reference [“Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900] the first voyage of Ermak is described as follows:

On the 5^thMarch, the Ermak sailed from the Tyne. Fast ice was met in the Gulf of Finland, between Reval and Hogland, the vessel passing through this difficulty; but, encountering severe pack ice, she stuck at times, and had to use ice-anchors in order to get free, the thickness of the pack-ice being estimated between 25 and 30 feet. It thus took the ship nearly three and a half days to pass from the beginning of the continuous ice to Kronstadt, but during that time the boat was stopped to allow some rest to the crew, which was not up to full strength. Though the end was successfully gained, it is evident that Admiral Makaroff was right in insisting in the power being not less than 10,000 IHP.” In a footnote in Reference [“Steamers for Winter Navigation and Ice-breaking”, Paper No. 3191 of the Proceedings of the Institution of Civil Engineers 1900] Ermak's initial experience in arctic waters is described in the following manner:

“Since the foregoing was written the Ermak has returned from her summer cruise in the Arctic Ocean, where she has not been entirely successful. After an attempt at the ice near Spitsbergen, she was taken back to Newcastle to have more web-frames and longitudinal stringers put in, some new plates replaced and a number of plates re-riveted. One blade of the fore propeller having broken, and the shaft having got out of line, it was decided to remove the fore propeller altogether, and the Ermak went on her second trip to force the Arctic ice; but this was hardly more encouraging, and her general seagoing qualities proved to be unsatisfactory, as might have been predicted from her highly inclined sides.

It should be remembered that the power of the fore propeller is only 25 percent of the total power, while according to American experience—successfully followed on the Sampo—it is desirable to have the power nearly equally divided, or, say 45 percent on the fore propeller. The comparative inefficiency of the Ermak may to some extent be explained by this disproportion.”

It should be noted that after removing the bow propeller it was possible to increase the steam pressure in the three remaining steam engines in order to increase the power of each from 1.56 MW to 1.88 MW for a total of 5.94 MW, or only a 5 percent reduction in total power. Runeberg also makes a comment about the well known fact that the conventional wedge shaped icebreaker hull form with inclined sides is highly inefficient in large waves.

Runebergs comment that the Ermak would have benefitted from more power in the bow is certainly correct in Baltic ice conditions as the displacement of the Ermak was almost four times larger than that of the Sampo while the power of the bow propeller was only 77% larger. It is described that better progress with Sampo in Baltic ice conditions is made by charging than by proceeding slowly and having the bow propeller alternating between full ahead and astern, as preferred on the Great Lakes. If you charge with high speed with the almost fourfold displacement and more than threefold power of the Ermak you will penetrate much further into the pack ice which considerably increases the possibility of becoming beset in the ice when compared to Sampo.

Runebergs comment that larger power on the bow propeller may have been of benefit in arctic ice conditions shows ignorance about the strength and thickness of old multi-year ice that unbroken will come in contact with a bow propeller fitted on a conventional wedge shaped bow when making the necessary charge with is the only possible method to force the ship through ice that cannot be penetrated with a continuous speed of advance. After the negative experience with the bow propeller of the Ermak no polar icebreaker has been seriously proposed to be fitted with bow propellers.

Following Ermak and Sampo the design of icebreakers intended for operation in open sea did not experience any major changes for almost 70 years, the major improvement being the installation of diesel-electric propulsion on the Swedish icebreaker Ymer built at Kockums in Malmö in 1933. This was a bold and successful experiment in order to improve fuel efficiency. The wedge shaped hull remained virtually unchanged with three propellers at the stern with a centerline rudder for polar icebreakers. For icebreakers intended for non polar operation the number of propellers gradually increased to four, two at the bow and two at the stern with a single centerline rudder. With increasing power levels the distance between the two stern propellers had to be increased with the result that the propeller streams could no longer reach the centerline rudder making this inefficient at low speeds.

After this period of stagnation several novel concepts have been tested in full scale the most important of which are listed below.

In 1969 Esso modified the oil tanker Manhattan to an icebreaking ship in order to test the feasibility of year round oil transport through the North West Passage. The tanker was fitted with two propellers and two rudders at the stern which after proper reinforcing operated satisfactorily even in multi-year ice, albeit the ship was unable to operating efficiently in the astern mode as the steam turbine machinery could only deliver 35% of the total power when backing.

In 1974 the Swedish government took delivery of Atle, the first icebreaker fitted with twin rudders built at the Wärtsilä shipyard in Helsinki, Finland. Initially both steering gears were connected by rods to each other. When running astern in heavy ice ridges the shear rings installed on these rods failed and some hours had to be spent replacing the shear rings. Once the two steering gears were separated the twin rudders operated fully satisfactorily.

In 1976 the US Coast Guard icebreaker Polar Star was delivered with a gas turbine machinery and controllable pitch propellers, a brave but unsuccessful experiment. As soon as the propellers operated in thick polar ice the pitch changing mechanism failed and the ship had to return to port for major repairs.

In 1979 Dome Petroleum of Calgary, Alberta, Canada took delivery of the combined icebreaker, anchor handling tug and supply ship Kigoriak built at Saint John Shipbuilding & Dry Dock Co Ltd in New Brunswick, Canada. This ship was fitted with a blunt spoon shaped bow and a single controllable pitch propeller protected by an extremely strong nozzle around the propeller. Operating aggressively in heavy multi-year ice while traversing the North West Passage on the delivery voyage from the builder's yard to the Beaufort Sea the protection provided by the nozzle was entirely demonstrated. Only relatively small pieces of ice are able reach the propeller blades inside the nozzle and thus the loads on the pitch changing mechanism are dramatically reduced. In addition as there is no wedging of ice between the propeller blade and the hull of the ship it is easy to reduce the pitch when ice enters the propeller and thus retain full rotational speed which is needed to enable the diesel engine to deliver full power. Kigoriak was also fitted with a bow lubrication system with pumps lifting large amounts of sea water on top of the ice in front of the bow in order to reduce the friction between the ice and the hull. This together with the considerable increase in power compared to the old Murtaja, removed the tendency to push ice ahead of the bow which had resulted in abandoning blunt bows on open sea icebreakers in 1890. Kigoriak was fitted with a relatively long parallel mid body with vertical sides. In order to make it possible to turn the ship in a solid ice cover she was fitted with reamers that made the bow portion 2 m wider than the mid ship portion and thus providing room for the stern to move sideways in the broken channel.

In 1986 the modified Russian icebreaker Mydyug was tested in relatively thick ice in the fjords of Spitsbergen, Reference [Günter R. Varges, Thyssen Nordseewerke GMBH: “Advances in Icebraker Design—The conversion of the Soviet Polar Icebraker Mydyug into a Thyssen/Waas Ship” 6^thWEMT Symposium Travemünde, Jun. 2 to 5, 1987]. The ship had originally been built in Finland with a wedge shaped bow with an average buttock angle of 24.4 degrees and an average frame angle of 49 degrees, a water line length of 79 m, a water line beam of 20 m, a draft of 6.5 m and a displacement of 6,211 tonnes. After the conversion, performed at the German shipbuilding company Thyssen Nordseewerke, the average buttock angle is 12 degrees, the average frame angle is 0 degrees—a totally flat bow—the water line length 93.2 m, the water line beam 20 m at the mid body and 22.2 m over the bow, the draft unchanged at 6.5 m and the displacement increased to 7,744 tonnes—about 25% larger than before the conversion. The propulsion power is the same, 7 MW, before and after the conversion. The new bow resulted in a dramatic increase in the thickness of ice the ship is able to break at a speed of 3 knots, it increased from about 0.8 m to about 1.5 m. The open water speed remained unchanged at 16.1 knots even if the displacement had increased by about 25%. The ship motions in a sea state improved radically with the new bow although slamming increased.

THE OBJECT

The main object of the present invention is to primarily solve the problem of, with a reasonable effect on the icebreaker in question, being able to break as wide a channel in the ice as is required and also efficiently be able to get the broken channel free from the majority of the broken ice.

THE SOLUTION

Said object is achieved by means of a device according to the present invention, which essentially is characterized in that the hull is formed of two functionally separate elements of different width, one upper and wider element of which is situated next to intended water line for breaking of unbroken ice, while a lower more slender element is intended for the transport of broken ice sideways and under the unbroken ice, that the wider element is provided with an essentially flat inclining front part and has a small frame angle, preferably less than 15°, and which also is arranged to break the ice downwards and having an essentially flat stern part, which is provided with a small frame angle, preferably less than 20° and which between front part and stern part has an essentially entirely flat lower portion, which is situated underneath the underside of the thickest level ice that the vessel is intended to break at continuous speed and simultaneously situated outside the width that said lower more slender element has, with front part, lower portion, and stern part situated at the maximal width of the vessel, and that the lower more slender element is provided with essentially vertical side portions and at the stem and stern in the direction of travel has a wedge-shape of a small opening angle, preferably less than 40°, when moving ahead, thanks to the wedge-shape, being arranged to force the ice broken thereby sideways and entirely or partly under the unbroken level ice, and when moving astern, thanks to the wedge-shape, force the broken ice sideways along stern part and lower portion for decreasing the amount of ice to contact the main propellers of the vessel.

DESCRIPTION OF THE DRAWINGS

The invention is described in the following in the form of a preferred embodiment example, reference being made to the accompanying drawings in which;

FIGS. 1 and 2 show two different three-dimensional views of a vessel having a device according to the present invention as seen obliquely from below from the stern and the stem, an upper hull part indicating element I and a lower hull part indicating element II, the upper element I at the deck showing a cantilever intended to decrease the risk of broken ice penetrating in onto the deck,

FIGS. 3 and 4 show in principle the same views as FIGS. 1 and 2 but only the part of the upper element I that is situated underneath the water line, more precisely the part of the hull that contacts broken and unbroken ice. FIGS. 1-4 show a version of the ship where the main propellers by lines of shafting are driven by machineries mounted inside the lower element II and a version wherein the vertical side portions of the lower element II are running continuously along the entire element,

FIG. 5 shows a line drawing of the vessel as seen from above,

FIG. 6 shows a line drawing of the vessel as seen from the side where it is seen how the inward inclining side portions amidships and at the afterbody are running parallel to the water line while they in the forebody are bent upwards since they are following the inclination of the flat bow portion,

FIG. 7 shows a line drawing of the vessel as seen from below indicating a version of the invention wherein the vertical side portions of the lower element II are not running continuously along the entire element but wherein they at the afterbody intersect a hull part that is more slender than the corresponding hull part of the mid ship,

FIG. 8 shows a body plan of the forebody of the vessel as seen from the front,

FIG. 9 shows a body plan of the forebody of the vessel as seen from the stern,

FIG. 10 shows a body plan of the afterbody of the vessel as seen from the stern where it is indicated how the full width of the bow provides a broken channel that is wider than the water line portions of the mid ship and the afterbody, which in turn decreases the friction between hull and ice and also contributes to the turning ability in ice by giving room for the afterbody to accelerate sideways until the upward breaking side portion contacts the unbroken ice to provide, by sideways icebreaking, a wider channel for the afterbody,

FIGS. 11 and 12 show the line drawings presented in FIGS. 6 and 7 extended with propellers and rudders,

FIG. 13 shows the wing or bow propeller as seen from the front,

FIG. 14 shows the wing or bow propeller as seen from the side,

FIG. 15 shows the wing or bow propeller as seen from above, and

FIGS. 16-18 show how the forebody of the ship when moving ahead in unbroken ice transports the broken ice under the unbroken ice by the side of the ship.

THE INVENTION

A new hull concept has been developed that consists of two elements I,II that functionally are totally different. In the upper part I a portion that comes into contact with unbroken ice 14 when moving ahead in a straight line is totally flat—the frame angle is zero—which breaks the ice and forces the broken pieces far enough down so that they may be transported sideways under the unbroken ice sheet on both sides of icebreaker. The lower element is wedge shaped at the bow and the stern and has vertical sides—the frame angle is 90 degrees against the horizontal—to efficiently push broken ice under the solid ice cover on both sides and also to provide support for propellers and rudders. When moving astern the novel hull form combination, presented in FIGS. 6,7 and 10, functions virtually in the same manner.

The new hull form combination is also provided with a novel type of reamer as may be seen in FIGS. 5-10. Reamers used so far on icebreakers or icebreaking ships are located at or close to the intersection between bow and mid body in order to create a broken channel that is wider than the mid body, which thus is able to turn in this wider channel. The new type of reamer presented here covers the entire distance from the most forward portion of the bow all the way to the most aft portion of the stern. To make it possible to turn in a solid ice cover the upper portion of the reamer in inclined in such a manner that it is able to break the ice upwards when the ship is turning, as shown in FIG. 10, thus providing room for the sideways movement of the ship. To prevent broken ice from reaching deck level during a turning maneuver a cantilever may be introduced well above the water line as shown in FIG. 18.

A propulsion configuration that augments the functions of the hull combination presented above is shown in FIGS. 11-18. The most radical novelty is to introduce bow propellers on icebreakers intended for operation in multi-year ice and to bring them back to icebreakers intended for operation in first year ice. The proposed bow propellers are, however, very different from bow propellers used previously. On the five icebreakers of Atle type delivered in the 1970's, the latest icebreakers provided with propellers in the front, the bow propellers are mounted on shafts that are directly connected to the electric propeller motors and thus the propeller stream will hit the side of the wedge shaped bow before being turned into a direction following the water lines of the ship. This greatly reduces the net thrust of the propeller and more seriously limits the possibility to transport broken ice within ice ridges towards the stern of the ship when the thickest portion of the ice ridge is located at or close to the widest part of the ship. When ramming into heavy ridges both bow propellers on an Atle type icebreaker will stall when the ice is compacted around the bow which very effectively will stop the ship. Then it will take some time to get the propellers rotating again and then some further time to free the ship from the embrace of the ice.

The bow propellers in this invention operate very differently as the propeller stream is directed along the wedge and away from the mid ship portion of the lower hull as shown in FIGS. 11 and 12. The propeller stream is also directed upwards in order to meet the bottom of the upper hull at an angle and thus forcing the broken ice under the solid ice cover when operating in level ice. In ice conditions where there is more ice around the ship the propeller stream will be forced towards the stern where there is room for the broken ice. The transport of ice towards the stern will be augmented by the propeller streams of one or several pairs of wing propellers, as also shown in FIGS. 11 and 12. The propeller stream caused by the main propellers located at the aft end of the lower hull will provide room for the broken ice behind the ship. Without the ice transport caused by the bow and wing propellers the thick ice in ridges will remain where it has been broken by the icebreaker and will thus remain as a main obstacle for ships following the icebreaker. The bow and wing propellers shown here will distribute the ice ridge over a much larger distance and thus make it easier for the assisted ships to follow in the track opened up by the icebreaker.

The configuration of the bow and wing propellers is shown in FIGS. 13-15. In order to achieve the necessary strength to withstand collisions with large and thick multi-year ice pieces the propeller is set at a fixed angle against the bottom of the upper hull which the propeller is flushing when the ship is processing in the forward direction. The nozzle is attached to a long extrusion fitted with a wing like portion at its leading edge in order to rotate large ice pieces away from the front of the nozzle. Protected by the nozzle is a controllable pitch propeller which is able to adjust the propeller pitch in such a manner that a constant propeller speed as well as the appropriate power level is maintained even when ice pieces are forced through the propeller disc. By keeping the propeller speed high it is easy for the propeller blades to efficiently cut the ice into pieces small enough to pass between the blades in order to join the propeller stream behind the propeller.

A body plan of the bow looking towards the stern is shown in FIG. 8. A body plan of the bow looking towards the front is shown in FIG. 9 and a body plan of the stern looking towards the front is shown in FIG. 10. The width of the upper hull must always be wide enough to provide protection for the bow and wing propellers. The hull form combination presented in FIGS. 6-10 shows an upper hull which is about two times wider than the lower hull but the upper hull may be considerably wider than this in order to efficiently assist large ships. It should be noted that the maximum width of existing icebreakers is about 30 m which is considerably smaller than the beam of large cargo ships needing icebreaker assistance. The reason for this is that a conventional wedge shaped icebreaker with 60 m width and 12 m draft will push most of the broken ice below the bottom of the ship and into the propulsion machinery. The form combination presented here does not have this problem and thus the maximum beam may be chosen to fit the ships being assisted.

The propulsion arrangement shown in FIGS. 11 and 12 includes two main propellers at the stern together with two large rudders, two wing propellers and two bow propellers. Normally the power of the main propeller would be chosen to be about equal to the combined power of the bow and wing propellers on one side of the ship in order to facilitate sideways movement of the ship at low speed in the same manner as used on conventional four propeller icebreakers. Controllable pitch propellers have the disadvantage that if the pitch is reversed without also reversing the rotation direction then the reverse thrust will suffer as a portion of the blades will operate in the wrong direction at full reverse power. But when the propeller is driven by an electric motor then the rotation direction may easily be reversed causing the controllable pitch propeller to be as efficient as a fixed pitch propeller in the reverse direction.

THE INVENTION IN MORE DETAIL

According to the invention, there is formed a device that is arranged for icebreaking with an icebreaking hull 2 of a ship 3 having a particular design of the hull 2. More precisely, a hull 2 is formed of two functionally separate elements I, II, which have different width B, D. An upper and wider element I is situated next to the water line 13 and is arranged for breaking of unbroken ice 14. A more slender element II situated under said element I is arranged for the transport of the broken ice 15 sideways and under the unbroken ice 14. The upper wider element I is provided with an essentially flat lower part portion of an inclining front part 10 and has a small frame angle a, preferably less than 15°, and which is arranged to break the ice 14 downwards when moving ahead F. Furthermore, the element I is provided with an essentially flat stern part 12, which is provided with a small frame angle c, preferably less than 20° and which is arranged to break the ice 14 downwards when moving astern R. Furthermore, between the front part 10 and stern part 12, there is arranged an entirely flat lower portion 11, which is situated underneath the underside of the thickest level ice that the ship 3 is intended to break at continuous speed, and simultaneously situated outside the width D that the lower more slender element II has. Outside the width D that said lower more slender element II has, with front part 10, lower portion 11, and stern part 12, there are arranged inward inclining side portions 4, 5 at the maximal width B of the vessel and with a relatively great frame angle e preferably between 45 and 60°, which when turning are arranged to break the ice upwards when operating in unbroken ice 14. The lower more slender element II is provided with essentially vertical side portions 7, 8, 9 and which at the stem 10 and at the stern 12 in the direction of travel has a wedge-shape of a small opening angle n,r, preferably less than 40°, when moving ahead F, thanks to the wedge-shape, being arranged to force the ice 15 broken thereby sideways and entirely or partly under the unbroken level ice 14, and when moving astern R, thanks to the wedge-shape, force the broken ice sideways along stern part 12 and lower portion 11 for decreasing the amount of ice to contact the main propellers 19 and rudder 20 of the vessel.

For the operation in ice, front part, lower portion, and stern part are, at the maximal width of the hull, accordingly provided with inward inclining side portions 4, 5 having a relatively great frame angle e to the water line, preferably between 45 and 60°, arranged to break the ice sideways and upwards when turning in unbroken ice.

The vessel is provided with at least two wing propellers 18, which are mounted at the bottom of the side portions 8 of the more slender element II of the hull, and which are directed so that the propeller stream upwards at a small angle u, preferably less than 10°, hits lower portions 11 of the upper element I in order to, in that connection, when moving ahead F accelerate the broken ice 15 aftwards and prevent the same ice from contacting the main propellers 19 of the ship.

The vessel is provided with at least two bow propellers 17, which are mounted at the bottom of the forward side portions 7 of the lower more slender element II directed in such a way that the propeller stream upwards at a small angle s, preferably less than 10°, and sideways at a small angle x, preferably half of the opening angle n, hits the lower portion 11 of said wider element I, so as to, when moving ahead F, in level ice accelerate the ice 15 broken thereby sideways under unbroken ice 14 and thereby essentially or entirely make the broken channel behind the ship 3 ice-free when operating in level ice and at continuous speed. When operating, for example in ice ridges, the lower part of which extends below the flat part 11 of the upper element I, the propeller stream created by the bow propellers 17 is directed astern, wherein the same, together with the propeller stream directed astern and created by the wing propellers 18, moves the major part of the ice ridge to the area abaft the vessel and which accordingly is spread over a larger area and decreases the ice resistance for trailing vessel. The wing and bow propellers 17, 18 are mounted on an extrusion 21 to decrease the contact of the propeller stream with the vertical side portions 7, 8 and a wing-like projecting element 22, preferably having a side length that at least extends to the centre of the propeller, is arranged in front of the wing and bow propellers 17, 18, to provide, together with the extrusion 21, rotation of broken ice-floes 15 and prevent the same from blocking the propellers 17, 18.

Propellers 17, 18 are arranged to rotate on a point of support at the sides of the vessel in ways which allow directing the propeller stream forwards or aftwards, upwards or downwards.

The main propellers 19 of the vessel are arranged to be rotated on points of support below the stern of the vessel in ways which allow directing the propeller stream forwards F or aftwards R, and arbitrarily towards both sides, which makes that the rudders 20 can be eliminated. The driving propellers 19 of the vessel are arranged to be driven by means of shaft from a propulsion machinery, which is situated in front of said propellers 19 in said lower more slender element II.

On the deck level, a cantilever 23 is provided, which decreases the risk of broken ice ending up on the deck 30 of the ship.

Function and nature of the invention should have been clearly understood from the above-mentioned and also with knowledge of what is shown in the drawings but the invention is naturally not limited to the embodiments described above and shown in the accompanying drawings. Modifications are feasible, particularly as for the nature of the different parts, or by using an equivalent technique, without departing from the protection area of the invention, such as it is defined in the claims.

Arrangement for Ice-Breaking

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