FI127090B

FI127090B - Icebreaking vessels

Info

Publication number: FI127090B
Application number: FI20155914A
Authority: FI
Inventors: Riku Kiili
Original assignee: Aker Arctic Tech Oy
Priority date: 2015-12-03
Filing date: 2015-12-03
Publication date: 2017-11-15
Also published as: FI20155914A

Description

Ice-breaking Vessel

The present invention relates to an ice-breaking vessel comprising a monohull, which has a longitudinal centerline, a first end and a second end, a bottom and a waterline, and which ice-breaking vessel is provided with propulsion devices, according to the preamble of claim 1. The present invention also relates to a method for operating an ice-breaking vessel in ice-conditions according to the preamble of claim 10. The present invention further relates to a method of breaking ice according to the preamble of claim 16.

Prior art

There are various kinds of ice-breaking vessels provided with turnable and fixed propulsion devices. US 5,218,917 discloses an ice-breaking vessel, in which the aft end of the vessel is designed to break ice efficiently. The vessel is provided with two turnable propulsion devices arranged in parallel at the aft end. US 5,996,520 discloses an icebreaker, which has three or four propulsion devices and which is arranged to move obliquely forward through an ice-field in order to open a passage in the ice-field that is broader than the hull of the icebreaker. The hull can be symmetric or asymmetric. The purpose is to assist wide vessels in ice conditions. WO 2009/007497 discloses an ice-breaking vessel provided with at least three propulsion devices arranged at one end of the ice-breaking vessel. The propulsion devices are arranged at least at two different distances from said one end, with at least two propulsion devices in parallel. The propulsion devices closer to said one end are used for breaking ice and the propulsion devices farther away from said one end are used to flush away broken ice when the vessel moves with the said one end ahead. US 8,398,445 discloses a marine vessel, particularly a drilling vessel, provided with azimuthing propulsion devices at both ends for station keeping of the vessel in varying ice conditions. WO 2013/119175 discloses a marine vessel for operating in icy waters. The vessel is provided with azimuthing propulsion devices positioned in a V- configuration at one end of the vessel in a corresponding manner as in WO 2009/007497.

All of the vessels mentioned above are provided with various positioning of propulsion devices in order to improve an ice-breaking operation or a positioning of the vessel. However, the load of the ice encountered in the ice-breaking operation is taken in full at one time as in traditional ice-breaking operations.

Summary of the invention

An object of the present invention is to achieve an ice-breaking vessel that avoids the drawbacks of prior art and that has an improved ice-breaking capability and that provides an excellent maneuverability. This is attained by an icebreaking vessel according to claim 1.

The basic idea of the invention is to provide an ice-breaking vessel with a lowered ice resistance and with an asymmetric configuration of the bottom or the waterline ensuring a phased ice-breaking operation.

This is achieved by providing the monohull of the ice-breaking vessel with an asymmetric waterline with respect to the longitudinal centerline at an icebreaking draft of the monohull at the first end or at the second end and by providing the monohull with a first ice-contact area on a first side of the longitudinal centerline at a first distance from the first end or the second end and with a second ice-contact area at a second side opposite the first side of the longitudinal centerline at a second distance from the first end or the second end. This provides the monohull with a capability for an advantageous phased ice-breaking sequence, whereby the ice in a first phase is broken or cracked at the forward part of the asymmetric first end or second end of the monohull at the first ice-contact area and subsequently in a second phase is turned down and pushed aside at the more aftward part of the first end or second end of the monohull at the second ice-contact area. Compared to a conventional icebreaking vessel, this arrangement also splits the ice and removes the ice from around the ice-breaking vessel more efficiently.

The distances, i.e. the first distance and the second distance, from the first end or the second end are considered to be taken in a longitudinal direction of the monohull, along the longitudinal centerline of the monohull taking into account the asymmetric design of the monohull, particularly of the waterline at said icebreaking draft of the monohull.

The “term ice-breaking vessel” defines a vessel that is intended to operate in ice infested waters or in ice-conditions at least to some degree. Such a vessel can be e.g. a tanker, a cargo ship, an offshore supply vessel, or other marine transport vessel, which typically also operates in open sea conditions. The vessel can also be an icebreaker.

The term “monohuH” defines a type of marine vessel having only one hull, unlike multihulled vessels, which can have two or more individual hulls connected to one another, e.g. vessels such as a catamaran or a trimaran.

Further, in this context, the terms “first end” and “second end” of the icebreaking vessel have been used instead of e.g. “front end” or “bow” and “aft end” or “stern” respectively, since the latter terms could be misinterpreted when the vessel is deployed and it moves forward with either end ahead in given operating conditions.

The ice-breaking vessel can be operated with either the first end or the second end ahead in a given travel direction, with the first end ahead or the second end ahead in ice-conditions in order to break ice in an ice-breaking operation.

The term “turnable propulsion device” defines an azimuthing propulsion device, which is turnable around a substantially vertical axis so that the direction of propulsion can be changed by turning the propulsion device. A device like this is known from e.g. US 5,403,216 and other prior art discussed above.

The term “waterline” relates to a waterline section of the hull shape at a certain draft.

The term “longitudinal vertical” relates to a vertical section of the hull shape at a certain breadth. In this field of technology this is also called “buttock line”.

The term “transverse vertical” relates to a transverse section of the hull at a certain longitudinal position. In this field of technology this is also called “frame section”.

The terms “midship” and “transverse center line” relate to the middle of the vessel in its longitudinal direction.

The terms “longitudinal centerline” and “direction of the longitudinal centerline” relate to the longitudinal direction of the ice-breaking vessel and to its movement aligned with the longitudinal centerline in open water or ice so that a minimum resistance to movement is achieved. The vessel can be provided with a keel extending along the longitudinal centerline of the monohull or offset from the longitudinal centerline of the monohull. In case the keel extends along the longitudinal centerline, the longitudinal centerline constitutes a keel line. Another term for “keel” used in this field of technology is “skeg”.

In an advantageous embodiment, the first ice-contact area includes a first icebreaking ridge at a first distance from the first end or the second end and the second ice-contact area includes a second ice-breaking ridge at a second distance from the first end or the second end. Such ridges can be slightly rounded or sharp. Sharp ridges are also called “knuckles”. This provides the monohull with an enhanced advantageous phased ice-breaking sequence, whereby the ice in a first phase is firstly broken or cracked by the first ice-breaking ridge and subsequently in a second phase is turned down and pushed aside by the second ice-breaking ridge. This also improves the splitting of the ice and the removal of ice from around the ice-breaking vessel.

In a further advantageous embodiment, an asymmetric vaulted portion, which is arranged to extend in the longitudinal direction of the monohull, is provided at the waterline at said ice-breaking draft at the first end or the second end. The asymmetric vaulted portion allows bending of the ice upwards within the asymmetric vaulted portion and facilitates the flow of broken ice away and aftwards of the vessel.

The terms “vault” and “vaulted” are to be interpreted so that the terms include also a more flat or plane surfaced configuration, i.e. not necessarily a clearly rounded configuration. The configuration can vary depending on the general design of the bottom of the monohull.

The asymmetric vaulted portion extending in the longitudinal direction of the monohull is advantageously arranged between the first ice-contact area and the second ice-contact area at the first end or the second end. This further improves the advantageous phased ice-breaking sequence, whereby the ice in a first phase is broken or cracked at the first ice-contact area and subsequently in a second phase turned down and pushed aside at the second ice-contact area. The asymmetric vaulted portion further allows bending of the ice upwards between the ice-contact areas and facilitates the flow of broken ice away and aftwards of the vessel.

If the vessel is provided with ice-breaking ridges, the asymmetric vaulted portion extending in the longitudinal direction of the monohull is advantageously arranged between the first ice-breaking ridge and the second ice-breaking ridge at the first end or the second end. This further improves the enhanced advantageous phased ice-breaking sequence, whereby the ice in a first phase is broken or cracked at the first ice-breaking ridge and subsequently in a second phase is turned down and pushed aside by the second ice-breaking ridge. The asymmetric vaulted portion further allows bending of the ice upwards between the ice-breaking ridges and facilitates the flow of broken ice away and aftwards of the vessel.

In an advantageous embodiment, the ice-breaking vessel is provided with at least a first turnable propulsion device and a second turnable propulsion device, which are arranged at different distances from the first end or from the second end, whereby the first turnable propulsion device is arranged in connection with the first ice-contact area and the second turnable propulsion device is arranged in connection with the second ice-contact area. The turnable propulsion devices assist in the ice-breaking operation and can also provide sideways flushing in both directions. The asymmetric vaulted portion, in addition to the positioning of the turnable propulsion devices, ensures sufficient water for the turnable propulsion devices.

Alternatively, the ice-breaking vessel is provided with at least a first turnable propulsion device and a second turnable propulsion device, which are arranged in parallel in a transverse direction of the monohull of the ice-breaking vessel. The first turnable propulsion device is arranged in connection with the first ice-contact area and the second turnable propulsion device is arranged in connection with the second ice-contact area. This arrangement also maintains the advantages provided by the asymmetric vaulted portion.

The ice-breaking vessel can also be provided with a keel and a keel line.

In an advantageous embodiment the keel is arranged offset from the longitudinal centerline of the monohull and at an angle to the longitudinal centerline of the monohull. Arranging the keel somewhat offset from the longitudinal center line and at an angle to the longitudinal centerline can be used to improve the directional stability of the asymmetric designed monohull.

The advantageous embodiments of the present invention are defined in claims 2-9.

The characterizing features of the method of operating an ice-breaking vessel in ice-conditions are given in claims 10-15.

The characterizing features of the method of breaking ice are given in claims 16-18.

Brief description of the drawings

In the following the invention will be described in more detail, by way of example only, with reference to the accompanying schematic drawings, in which

Fig. 1 shows a first embodiment of the present invention in a first mode of operation,

Fig. 2 shows a set of longitudinal verticals taken at sections A-A, B-B and C-C as indicated in Fig. 1,

Fig. 3 shows a set of transverse verticals taken at sections D-D and E-E as indicated in Fig. 1,

Fig. 4 shows a second embodiment of the present invention in said first mode of operation,

Fig. 5 shows a third embodiment of the present invention in said first mode of operation,

Fig. 6 shows a set of longitudinal verticals taken at sections A-A, B-B and C-C as indicated in Fig. 5,

Fig. 7 shows a set of transverse verticals taken at sections D-D and E-E as indicated in Fig. 5,

Fig. 8 shows the third embodiment of the present invention in a second mode of operation,

Fig. 9 shows the third embodiment of the present invention in a third mode of operation,

Fig. 10 shows the third embodiment of the present invention in a fourth mode operation,

Fig. 11 shows a fourth embodiment of the present invention in said first mode of operation,

Fig. 12 shows a fifth embodiment of the present invention in said first mode of operation,

Fig. 13 shows a perspective view of the monohull of the ice-breaking vessel according to the present invention,

Fig. 14 shows a sixth embodiment of the present invention in said first mode of operation,

Fig. 15 shows a seventh embodiment of the present invention in said first mode of operation,

Fig. 16 shows an eighth embodiment of the present invention in said first mode of operation,

Fig. 17 shows a transverse vertical at section F-F as indicated in Fig. 16,

Fig. 18 shows a ninth embodiment of the present invention in said first mode of operation,

Fig. 19 illustrates the ice breaking method of the present invention,

Fig. 20 illustrates a transverse vertical D-D view as indicated in Fig. 19, and Fig. 21 illustrates a transverse vertical E-E view as indicated in Fig. 19.

Detailed description

Fig. 1 illustrates a first embodiment of an ice-breaking vessel 1 according to the present invention comprising a monohull 2 with a second end 22 and a first end 21 (not shown) in a longitudinal direction of the monohull 2. The icebreaking vessel 1 is provided with at least two turnable propulsion devices each of which is arranged at a different distance from the second end 22 of the monohull 2. The turnable propulsion devices are used for providing propulsion power as well as for steering for the vessel in a manner known to a person skilled in the art. In addition the turnable propulsion devices assist in the icebreaking operation of the ice-breaking vessel 1.

The monohull 2 has a bottom 24, a longitudinal centerline LCL, which extends in the longitudinal direction of the monohull, a keel 23, which extends a given distance along the bottom 24 in the direction of the longitudinal centerline LCL of the monohull 2, a waterline and a deck 3. A part of the bottom is asymmetric at the second end 22 with respect to the longitudinal centerline LCL of the monohull 2. The waterline 5 at an ice-breaking draft is asymmetric with respect to the longitudinal centerline LCL as indicated by a bold line. The monohull 2 also has an asymmetric vaulted portion 10 extending in the longitudinal direction of the monohull 2 at the waterline 5 at said ice-breaking draft at the second end 22.

In this embodiment also a part of the bottom 24 below the waterline 5 at said ice-breaking draft is asymmetric as indicated by a thinner line 51. Further towards midship, the bottom 24 below the waterline 5 at the ice-breaking draft is symmetric around the keel 23 as indicated by thinner lines 52 and 53.

In this embodiment the deck 3 is asymmetric with respect to the longitudinal centerline LCL at the second end 22 of the monohull 2. Alternatively, the deck 3 can also be symmetric as shown in Figs. 16 and 18.

The second end 22 of the monohull 2 has an asymmetric design with respect to the longitudinal centerline LCL of the monohull 2.

Fig. 1 illustrates the first embodiment of the ice-breaking vessel 1 in a first mode of operation, in which it moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

In this embodiment, the monohull 2 is provided with a first ice-contact area 91 and with a second ice-contact area 92 at the second end 22. The first ice-contact area 91 and the second ice-contact area 92 are arranged asymmetrically with respect to the longitudinal centerline LCL and at different distances from the second end 22 of the monohull 2 and form ice-breaking areas at the waterline 5 at said ice-breaking draft. The first ice-contact area 91 is closer to the second end 22 and the second ice-contact area 92 is farther away from the second end 22. The first ice-contact area 91 is thus arranged on a first side of the longitudinal centerline LCL at a first distance from the second end 22 and the second ice-contact area 92 is arranged on a second side opposite said first side of the longitudinal centerline LCL at a second distance the second end 22.

The two turnable propulsion devices include a first turnable propulsion device 71 arranged at a first distance from the second end 22 and a second turnable propulsion device 72 arranged at a second distance from the second end 22. Each turnable propulsion device is provided with a propeller 75. The said distance can also be calculated from the first end 21. The first turnable propulsion device 71 and the second turnable propulsion device 72 are thus not aligned in a transverse direction of the monohull 2. The first turnable propulsion device 71 is closer to the second end 22 and the second turnable propulsion device 72 is farther away from the second end 22.

In this embodiment, the propeller 75 of the first turnable propeller device 71 and the propeller 75 of the second turnable propeller device 72 are positioned in the front in the travel direction of the ice-breaking vessel, i.e. towards the ice. This positioning enables the turnable propulsion devices with their propellers 75 to assist in the breaking of ice and in pulling the vessel towards the ice in a first phase and subsequent second phase of the ice-breaking operation (discussed in detail below).

The first turnable propulsion device 71 is located in connection with the first ice-contact area 91 and the second turnable propulsion device 72 is located in connection with the second ice-contact area 92.

The asymmetric design of the monohull, i.e. of the second end, provides for a phased ice-breaking operation. The more forward part, including the first ice-contact area 91, of the second end 22 of the monohull 2 with the first turnable propulsion device 71 engages with the ice in a first phase splitting the ice and subsequently the more aftward part, including the second ice-contact are 92, of the second end 22 of the monohull 2 with the second turnable propulsion device 72 engages with the ice in a second phase and finalizes the icebreaking. Such a two-phased ice-breaking operation requires less propulsion power than a one-phased ice-breaking operation to achieve the same icebreaking speed. Such a phased ice-breaking operation thus results in a lesser ice-breaking resistance.

In addition, as the propulsion devices are not arranged in parallel, the risk of blocking ice-formations between the propulsion devices is avoided.

Two propulsion devices arranged in parallel also set a certain requirement with regard to the breadth of a hull of a vessel. When the propulsion devices are positioned asymmetrically with respect to the longitudinal centerline LCL (non-aligned with a transverse direction of the monohull), i.e. at different distances from the first end, or the second end, of the monohull, the breadth of the monohull can be reduced. This lessens the ice-breaking resistance of the vessel, thus also reducing the required propulsion power.

The asymmetric design of the monohull also provides for some inherent pitching and heeling from side to side of the vessel, which provides an additional ice-breaking effect.

The asymmetric design of the monohull further reduces slamming when the vessel moves forward in its travel direction. This improves the seaworthiness of the vessel, particularly in heavy seas.

The distances, i.e. the first distance and the second distance, from the first end or the second end are considered to be taken in the longitudinal direction of the monohull, along the longitudinal centerline of the monohull taking into account the asymmetric design of the monohull.

From Fig. 1 and Fig. 2 it can be seen that the first ice-contact area 91 (section C-C of Fig. 1) is located closer to the second end 22 than the second ice-contact area 92 (section A-A of Fig. 1). In practice this means that a longitudinal vertical (section A-A of Fig. 1) taken at the second ice-contact area 92 has a somewhat gentler slope (is less inclined) than a longitudinal vertical (section C-C of Fig. 1), which has a somewhat steeper slope (is more inclined), taken at the first ice-contact area 91. This further enhances the phased ice-breaking operation discussed above in connection with Fig. 1. In the first phase, the first ice-contact area 91 cracks the ice when it engages with the ice, where after, in the subsequent second phase, the second ice-contact area 92, with a gentler slope, mainly bends and pushes the ice away from the ice-breaking vessel when it engages with the ice, and bends the ice upwards towards a summit of the asymmetric vaulted portion 10 (discussed more in detail below) at the waterline 5 at said ice-breaking draft of the monohull. In principle the waterline 5 at said ice-breaking level is as a whole in contact with the ice, but the ice-contact areas provide the two-phased ice-breaking operation.

The energy required for the first phase and the second phase is thus reduced, which results in a lower power requirement. The slopes of the longitudinal verticals can be different than described above depending of the design of the monohull.

The first end 21 of the monohull 2 can also be provided with corresponding ice-contact areas and turnable propulsion devices in a similar manner as the second end 22 as is discussed in connection with the second embodiment described below in connection with Fig. 4

Fig. 1 and Fig. 3 illustrate the asymmetric vaulted portion 10 extending in the longitudinal direction of the monohull 2 and being arranged at the waterline 5 at said ice-breaking draft. In this embodiment the asymmetric vaulted portion is arranged between the first ice-contact area 91 and the second ice-contact area 92 at the second end 22. Each of the two turnable propulsion devices is arranged in connection with an ice-contact area, on opposite sides of the asymmetric vaulted portion 10 and the longitudinal centerline LCL at the second end 22.

The asymmetric vaulted portion 10 receives and facilitates the removal of ice that has been broken by the ice-breaking vessel in the first phase and the subsequent second phase as discussed above. Slamming is also further reduced due to the upwards concave channel in the monohull 2 formed by the asymmetric vaulted portion 10, particularly in heavy seas. The asymmetric vaulted portion 10 forms a vault, the summit of which is towards the deck 3 of the icebreaking vessel 1.

The above also describes the method of operating an ice-breaking vessel in ice conditions as further defined in claims 10-14 taking into consideration that ice-breaking ridges are not disclosed in this embodiment.

The asymmetric vaulted portion 10 and its asymmetric form are also illustrated in Fig. 2 and Fig. 3. Fig. 2 shows a longitudinal vertical (section B-B of Fig. 1) taken between the first ice-contact area 91 and the second ice-contact area 92. Fig. 3 shows a transverse vertical (section D-D of Fig. 1) taken at the first ice-contact area 91 and a transverse vertical (section E-E of Fig. 1) taken at the second ice-contact area 92 at the waterline 5 at said ice-breaking draft. The asymmetric vaulted portion 10 thus provides an upwards concave form at or in the area of the level of the waterline 5 at said ice-breaking draft.

In Figs. 1-3 the asymmetric vaulted portion is shown with a rounded configuration. The asymmetric vaulted portion can also a more flat or plane surfaced configuration, i.e. not necessarily a clearly rounded configuration. The configuration can vary depending on the general design of the bottom of the monohull.

In a corresponding manner as the ice-contact areas and the turnable propulsion devices, the asymmetric vaulted portion can also be provided at the first end 21 of the monohull as is discussed in connection with the second embodiment described below in connection with Fig. 4.

Various modes of operation of the ice-breaking vessel, mainly relating to a positioning of the turnable propulsion devices, will be described more in detail below in connection with Figs. 5 and 8-10 discussing a third embodiment of an ice-breaking vessel, and thus apply to this first embodiment as well.

Fig. 4 illustrates a second embodiment of an ice-breaking vessel 1 comprising a monohull 2 with a first end 21 and a second end 22 in a longitudinal direction of the monohull. The ice-breaking vessel 1 is provided with at least four turnable propulsion devices each of which is arranged at a different distance from the first end 21 or the second end 22 of the monohull 2.

The second embodiment corresponds to the first embodiment. Flowever, the second embodiment illustrates that both the first end and the second end are asymmetrically designed and provided with asymmetrically arranged ice-contact areas and asymmetrically positioned turnable propulsion devices.

In Fig. 4 the ice-breaking vessel is shown in said first mode of operation, whereby the vessel moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

The monohull 2 has a bottom 24, a longitudinal centerline LCL, which extends in the longitudinal direction of the monohull, a keel 23, which extends a given distance along the bottom 24 in the direction of the longitudinal centerline LCL of the monohull 24, a waterline and a deck 3. The waterline 5 at an icebreaking draft is asymmetric at the first end 21 and the second end 22 as indi cated by a bold line. Below the waterline 5 at said ice-breaking draft the bottom 24 is partly asymmetric as indicated by a thinner line 51 and then symmetric towards a transverse center line TCL and around the keel 23 as indicated by thinner lines 52 and 53.

In this embodiment the deck 3 is asymmetric at the first end 21 and the second end 22 with respect to the longitudinal centerline LCL of the monohull 2. Alternatively, the deck can also be symmetric as shown in Figs. 16 and 18.

More particularly, the vessel 1 is provided with a first turnable propulsion device 71 arranged at a first distance from the first end 21, a second turnable propulsion device 72 arranged at a second distance from the first end 21, a third turnable propulsion device 72 arranged at a third distance from the first end 21 and a fourth turnable propulsion device 74 arranged a fourth distance from the first end 21. These distances may in a corresponding manner also be calculated from the second end 22. Each turnable propulsion device is provided with a propeller 75. The turnable propulsion devices are not aligned in a transverse direction of the monohull, i.e. they are arranged asymmetrically with respect to the longitudinal centerline LCL. The first turnable propulsion device 71 is closer to the second end 22 and the second turnable propulsion device 72 is farther away from the second end 22. In a corresponding manner the third turnable propulsion device 73 is closer to the first end 21 and the fourth turnable propulsion device 74 is farther away from the first end 21.

In this embodiment the monohull 2 has an asymmetric design with respect to the longitudinal centerline LCL of the monohull. With respect to the transverse centerline TCL the monohull is symmetric.

In this embodiment, the first end 21 and the second end 22 are provided with a first ice-contact area 91 at a first distance from the first end 21 and the second end 22 respectively and with a second ice-contact area 92 at a second distance from the first end 21 and the second end 22 respectively. The first ice-contact area 91 and the second ice-contact area 92 are located at the area of the bottom 24 of the monohull 2, below the waterline 5 at said ice-breaking draft. The first ice-contact are 91 is closer to the first end 21 and the second end 22 respectively and the second ice-contact area 92 is farther away from the first end 21 and the second end 22 respectively.

The description above in connection with Figs. 2 and 3 apply to this embodiment as well. The corresponding sections A-A, B-B, C-C, D-D and E-E are indicated in Fig. 4. These relate to both the first end 21 and the second end 22 of the monohull 2 of the second embodiment, although they are not specifically described in detail.

Fig. 5 illustrates a third embodiment of an ice-breaking vessel 1 according to the present invention comprising a monohull 2 with a second end 22 and a first end 21 (not shown) in a longitudinal direction of the monohull 2. The icebreaking vessel 1 is provided with at least two turnable propulsion devices each of which is arranged at a different distance form the second end 22 of the monohull 2. The turnable propulsion devices are used for providing propulsion power as well as for steering for the vessel in a manner known to a person skilled in the art. In addition the turnable propulsion devices assist in the icebreaking operation of the ice-breaking vessel 1.

The monohull 2 has bottom 24, a longitudinal centerline LCL, which extends in the longitudinal direction of the monohull, a keel 23, which extends a given distance along the bottom 24 in the direction of the longitudinal centerline LCL of the monohull 24, a waterline and a deck 3. A part of the bottom is asymmetric at the second end 22 with respect to the longitudinal centerline LCL of the monohull 2. The waterline 5 at an ice-breaking draft is asymmetric with respect to the longitudinal centerline LCL as indicated by a bold line. The monohull 2 also has an asymmetric vaulted portion 10 extending in the longitudinal direction of the monohull 2 at the waterline 5 at said ice-breaking draft at the second end 22.

In this embodiment also a part of the bottom below the waterline 5 at said icebreaking draft is asymmetric as indicated by a thinner line 51. Further towards midship, the bottom 24 below the waterline 5 at said ice-breaking draft is symmetric around the keel 23 as indicated by thinner lines 52 and 53.

Fig. 5 illustrates the third embodiment of the ice-breaking vessel 1 in a first mode of operation, in which it moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

In this embodiment, the first ice-contact area 91 at the second end 22 is provided with a first ice-breaking ridge 81 and the second ice-contact area 92 at the second end 22 is provided with a second ice-breaking ridge 82.

The first ice-contact area 91 is arranged on a first side of the longitudinal centerline LCL at a first distance from the second end 22 and the second ice-contact area 92 is arranged on a second side opposite said first side of the longitudinal centerline LCL at a second distance from the second end 22.

The first ice-breaking ridge 81 provides a first ice-breaking point 811 at the waterline 5 at said ice-breaking draft. The second ice-breaking ridge 82 provides a second ice-breaking point 821 at the waterline 5 at said ice-breaking draft. The ice-breaking ridges are arranged asymmetrically with respect to the longitudinal centerline LCL and at different distances from the second end 22 of the monohull 2. The first ice-breaking ridge 81 is closer to the second end 22 and the second ice-breaking ridge 82 is farther away from the second end 22.

In this embodiment, the propeller 75 of the first turnable propeller device 71 and the propeller 75 of the second turnable propeller device 72 are positioned in the front in the travel direction of the ice-breaking vessel, i.e. towards the ice. This positioning enables the turnable propulsion devices with their respective propellers 75 to assist in the breaking of ice and in pulling the vessel towards the ice in a first phase and subsequent second phase of the icebreaking operation (discussed in detail below).

The first ice-breaking ridge 81 extends at least from the level of the waterline 5 at said ice-breaking draft of the monohull 2 to the vicinity of the first propulsion device 71 (in connection with the first ice-contact area 91) and the second icebreaking ridge 82 extends at least from the level of the waterline 5 at said icebreaking draft of the monohull 2 to the vicinity of the second turnable propulsion device 72 (in connection with the second ice-contact area 92).

The asymmetric design of the monohull, i.e. of the second end, provides for a phased ice-breaking operation. The more forward part of the second end 22 of the monohull 2, including the first ice-contact area 91 with the first ice-breaking ridge 81, with the first turnable propulsion device 71 engages with the ice in a first phase splitting the ice and subsequently the more aftward part of the second end 22 of the monohull 2, including the second ice-contact area 92 with the second ice-breaking ridge 82, with the second turnable propulsion device 72 engages with the ice and finalizes the ice-breaking in a second phase. Such a two-phased ice-breaking operation requires less propulsion power than a one-phased ice-breaking operation to achieve the same ice-breaking speed. Such a phased ice-breaking operation thus results in a lesser ice-breaking resistance.

In addition, as the propulsion devices are not arranged in parallel the risk of blocking ice-formations between the propulsion devices is avoided.

From Fig. 5 and Fig. 6 it can be seen that the first ice-breaking ridge 81 (section C-C of Fig. 5) is shorter than the second ice-breaking ridge 82 (section A-A of Fig. 5). In practice this means that a longitudinal vertical (section A-A of Fig. 5) taken at the second ice-breaking ridge 82 has a somewhat gentler slope (is less inclined) than a longitudinal vertical (section C-C of Fig. 5), which has a somewhat steeper slope (is more inclined), taken at the first ice-breaking ridge 81. This further enhances the phased ice-breaking operation discussed above in connection with Fig. 1 and Fig. 5 above. In the first phase, the first ice-breaking ridge 81 cracks the ice when it engages with the ice, where after, in the subsequent second phase, the second ice-breaking ridge 82, with a gentler slope, engages with the ice and mainly bends and pushes the ice away from the ice-breaking vessel, and bends the ice upwards towards a summit of an asymmetric vaulted portion 10 (discussed more in detail below) at the waterline 5 at said ice-breaking draft of the monohull 2. In principle the waterline 5 at said ice-breaking level is as a whole in contact with the ice, but the ice-contact areas with their respective ice-breaking ridges provide the two-phased ice-breaking operation.

The energy required for the first phase and the second phase is thus reduced, which results in a lower power requirement. The slopes of the longitudinal verticals can be different than described above depending on the design of the monohull.

The first end 21 of the monohull 2 can also be provided with corresponding ice-contact areas, ice-breaking ridges and turnable propulsion devices in a similar manner as the second end 22 as discussed in connection with the fourth embodiment described below in connection with Fig. 11.

Fig. 5 and Fig. 7 illustrate an asymmetric vaulted portion 10 extending in the longitudinal direction of the monohull 2 and being arranged at the waterline 5 at said ice-breaking draft. In this embodiment the asymmetric vaulted portion 10 is arranged between the first ice-breaking ridge 81 and the second icebreaking ridge 82 at the second end 22 of the monohull 2. Each of the two turnable propulsion devices is arranged in connection with an ice-breaking ridge, on opposite sides of the asymmetric vaulted portion 10 and the longitudinal centerline LCL at the second end 22.

The asymmetric vaulted portion 10 receives and facilitates the removal of ice that has been broken by the ice-breaking vessel in the first phase and the subsequent second phase as discussed above. Slamming is also further reduced due to the upwards concave channel in the monohull 2 formed by the asymmetric vaulted portion 10 at the bottom area of the monohull, particularly in heavy seas. The asymmetric vaulted portion 10 thus forms a longitudinal vault, the summit of which is upwards, i.e. towards the deck 3 of the ice-breaking vessel 1.

The asymmetric vaulted portion 10 and its asymmetric form are also illustrated in Fig. 5 and Fig. 6. Fig. 6 shows a longitudinal vertical (section B-B of Fig. 5) taken between the first ice-breaking ridge 81 and the second ice-breaking ridge 82. Fig. 7 shows a transverse vertical (section D-D of Fig. 5) taken at the first ice-breaking point 811 at the waterline 5 at said ice-breaking draft and a transverse vertical (section E-E of Fig. 5) taken at the second ice-breaking point 821 at the waterline 5 at said ice-breaking draft. The asymmetric vaulted portion 10 thus provides an upwards concave form at or in the area of the level of the waterline 5 at said ice-breaking draft.

In a corresponding manner as the ice-contact areas, the ice-breaking ridges and the turnable propulsion devices, the asymmetric vaulted portion can also be provided at the first end 21 of the monohull 2 as is discussed in connection with the fourth embodiment described in connection with Fig. 11.

Fig. 7 also indicates sections G-G and H-H, which will be discussed later on in connection with Figs. 19-21.

Fig. 8, illustrating a second mode of operation of the third embodiment of icebreaking vessel 1 according to the invention, shows how the first turnable propulsion device 71 and the second turnable propulsion device 72 are turned with their respective propellers 75 towards the longitudinal centerline LCL, i.e. in a transverse direction to the longitudinal direction of the monohull 2. This positioning provides a possibility for an effective sideways flushing operation, whereby the propeller streams do not interfere with each other. This improves the ice-management capabilities of the vessel. Thus, the body of water around the vessel can be kept clear of ice. This also provides for an improved dynamic positioning of the vessel.

This would not be possible, if the turnable propulsion devices would be arranged in parallel at one or both ends the vessel. In such an arrangement, the turning of the turnable propulsion devices with the propellers against each other, the propellers would come too close to each other and not have sufficient water for optimal operation. This would cause undesired cavitation, vibration and noise. The power output would have to be kept very low in order to avoid damages to the propulsion devices, which again would result in inefficient flushing.

Fig. 9, illustrating a third mode of operation of the third embodiment of the icebreaking vessel 1 according to the present invention, shows how the both the first turnable propulsion device 71 as well as the second turnable propulsion device 72 with their respective propellers 75 are turned in the same sideways direction, i.e. in a transverse direction to the longitudinal centerline LCL of the monohull 2. This positioning provides for an effective full sideways push, e.g. in a dynamic positioning operation.

This would not be possible, if the turnable propulsion devices would be arranged in parallel at one or both ends of the vessel.

The ice-breaking vessel according to the present invention thus has increased ice-management capabilities and increased maneuvering agility.

Particularly in the second and third mode of operation, and in comparison to an arrangement where the turnable propulsion devices would be arranged in parallel at one or both ends of the vessel, the present invention allows for using more power in the turnable propulsion devices.

Fig. 10 illustrates a fourth mode of operation of the third embodiment of the ice-breaking vessel 1 according to the present invention, in which the vessel moves with the first end 21 ahead. In this fourth mode of operation, the first turnable propulsion device 71 and the second turnable propulsion device 72 are turned so that the propeller 75 of each turnable propulsion device is turned in the direction of the first end 21 in a pulling mode. In principle, if only the second end 22 of the ice-breaking vessel would have the particular configura- tion as described above, this would be a mode of operation for travelling in open seas first end 21 ahead.

In Figs. 5-10 the asymmetric vaulted portion is shown with a rounded configuration. The asymmetric vaulted portion can also a more flat or plane surfaced configuration, i.e. not necessarily a clearly rounded configuration. The configuration can vary depending on the general design of the bottom of the monohull.

The above also describes the method of operating an ice-breaking vessel in ice conditions as further defined in claims 10-14.

Fig. 11 illustrates a fourth embodiment of an ice-breaking vessel 1 according to the present invention comprising a monohull 2 with a first end 21 and a second end 22 in a longitudinal direction of the monohull. The ice-breaking vessel 1 is provided with at least four turnable propulsion devices each of which is arranged at a different distance form the first end 21 or the second end 22 of the monohull 2.

The fourth embodiment corresponds to the third embodiment. Flowever, the fourth embodiment illustrates that both the first end and the second end are asymmetrically designed and provided with asymmetrically arranged ice-contact areas, including ice-breaking ridges, and provided with asymmetrically positioned turnable propulsion devices.

The monohull 2 has a bottom 24, a longitudinal centerline LCL, which extends in the longitudinal direction of the monohull, a keel 23, which extends a given distance along the bottom 24 in the direction of the longitudinal centerline LCL, a waterline and a deck 3. The waterline 5 at an ice-breaking draft is asymmetric with respect to the longitudinal centerline LCL at the first end 21 and the second end 22 as indicated by a bold line. Below the waterline 5 at said icebreaking draft the bottom 24 is partly asymmetric as indicated by a thinner line 51 and then symmetric towards a transverse center line TCL and around the keel 23 as indicated by thinner lines 52 and 53.

In this embodiment the deck 3 is asymmetric at the first end 21 and the second end 22 with respect to the longitudinal centerline LCL of the monohull 2. Alternatively, the deck can also be symmetric as shown in Fig. 16 and Fig. 18.

In Fig. 11 the ice-breaking vessel is shown in said first mode of operation, whereby the vessel moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

In this embodiment, the first ice-contact area 91 at the first end 21 and the second end 22 is provided with a first ice-breaking ridge 81 at a first distance from the first end 21 and the second end 22 respectively and the second ice contact area 92 at the first end 21 and the second end 22 is provided with a second ice-breaking ridge 82 at a second distance from the first end 21 and the second end 22 respectively. The first ice-contact are 91 with the first icebreaking ridge 81 is closer to the first end 21 and the second end 22 respectively and the second ice-contact area 92 with the second ice-breaking ridge 82 is farther away from the first end 21 and the second end 22 respectively.

The first ice-breaking ridge 81 provides a first ice-breaking point 811 at the waterline 5 at said ice-breaking draft at both ends of the vessel. The second icebreaking ridge 82 provides a second ice-breaking point 821 at the waterline 5 at said ice-breaking draft at both ends of the vessel. The first ice-breaking ridge 81 and the second ice-breaking ridge 82 extend at least from the level of the waterline 5 at said ice-breaking draft of the monohull 2 to the vicinity of the respective first, second, third and fourth turnable propulsion devices 71, 72, 73 and 74.

The description above in connection with Figs. 6 and 7 apply to this embodiment as well. The corresponding sections A-A, B-B, C-C, D-D and E-E are indicated in Fig. 11. These relate to both the first end 21 and the second end 22 of the monohull 2 of the fourth embodiment, although they are not specifically described in detail.

Fig. 12 illustrates a fifth embodiment of the ice-breaking vessel according to the present invention comprising a monohull 2 with a first end 21 and a second end 22 in a longitudinal direction of the monohull. The ice-breaking vessel 1 is provided with at least four turnable propulsion devices each of which is arranged at a different distance form the first end 21 or the second end 22 of the monohull 2.

In principle this fifth embodiment corresponds to the second embodiment described above in connection with Fig. 4 and is therefore not discussed in greater detail in this connection. Flowever, in this embodiment the monohull 2 has an asymmetric design with respect to the longitudinal centerline LCL of the monohull and also with respect to the transverse center line TCL of the monohull. This illustrates that the asymmetric design of the first end and the second end of the monohull can vary and thus be applied in view of optimal operation of the ice-breaking vessel in varying circumstances.

This asymmetric design can also be applied e.g. to the fourth embodiment of Fig. 11 and the ninth embodiment of Fig. 18.

Fig. 12 illustrates the fifth embodiment of the ice-breaking vessel 1 in a first mode of operation, in which it moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

The monohull 2 has a bottom 24, a longitudinal centerline LCL, which extends in the longitudinal direction of the monohull, a keel 23, which extends a given distance along the bottom in the direction of the longitudinal centerline LCL, a waterline and a deck 3. The bottom is partly asymmetric at the first end 21 and the second end 22 with respect to the longitudinal centerline of the monohull. The waterline 5 at an ice-breaking draft is asymmetric with respect to the longi tudinal centerline LCL at the first end 21 and the second end 22 as indicated by a bold line. Below the waterline 5 at said ice-breaking draft the bottom 24 is partly asymmetric as indicated by a thinner line 51 and then symmetric towards a transverse center line TCL and around the keel 23 as indicated by thinner lines 52 and 53.

In this embodiment the deck 3 is asymmetric at the first end 21 and the second end 22 with respect to the longitudinal centerline LCL of the monohull 2. Alternatively, the deck can also be symmetric as shown in Fig. 16 and 18.

More particularly, the vessel 1 is provided with a first turnable propulsion device 71 arranged at a first distance from the second end 22, a second turnable propulsion device 72 arranged at a second distance from the second end 22, a third turnable propulsion device 73 arranged at a third distance from the second end 22 and a fourth turnable propulsion device 74 arranged a fourth distance from the second end 22. These distances may in a corresponding manner also be calculated from the first end 21. Each turnable propulsion device is provided with a propeller 75. The turnable propulsion devices are not aligned in a transverse direction of the monohull, i.e. they are asymmetrically arranged with respect to the longitudinal centerline LCL of the monohull 2.

The difference in the asymmetric design as compared to the second embodiment effect the position of the first ice-contact area 91 and the second ice-contact area 92, as well as the position of the third turnable propulsion device 73 and the fourth turnable propulsion device 74 at the first end 21 vis-å-vis the vicinity to the first end 21.

The various modes of operation, i.e. the positioning of the turnable propulsion devices as described in connection with Figs. 5 and 8-10, apply to this second embodiment as well and are therefore not repeated in this connection.

Fig. 13 provides a perspective view from below of the asymmetrically designed monohull 2 of the ice-breaking vessel 1 according to the present invention indicating the various longitudinal verticals and transverse verticals as discussed and shown above in connection with Figs. 1-3, Fig. 4, Figs. 5-7, Fig. 11 and Fig. 12.

Fig. 14 illustrates a sixth embodiment of the ice-breaking vessel according to the present invention. This fifth embodiment corresponds in general to the first embodiment described in connection with Figs. 1-3 above and will therefore not be discussed in detail in this connection.

The principal difference between this sixth embodiment and the first embodiment is that the first turnable propulsion device 71 and the second turnable propulsion device 72, with their respective propellers 75, are installed in parallel in a transverse direction of the monohull 2 at the second end 22 of the monohull 2 of the ice-breaking vessel 1, i.e. symmetrically with respect to the longitudinal centerline LCL.

The consequence of this positioning is that the advantages provided by the transversely non-aligned turnable propulsion devices described in connection with the second embodiment cannot be achieved.

However, all the benefits of the asymmetrically designed second end 22 of the monohull 2, also with a correspondingly designed first end 21 of the monohull 2, including the ice-contact areas, as well as the asymmetric vaulted portion, can nonetheless be achieved. Thus, this sixth embodiment provides for an advantageous result in less demanding circumstances.

The various modes of operation, i.e. the positioning of the turnable propulsion devices as described in connection with Figs. 1, 5 and 8-10, apply in principle to this sixth embodiment as well and are therefore not repeated in this connection.

This embodiment is intended for the method of operating an ice-breaking vessel in ice conditions as further defined in claims 10-13 and 15 taking into consideration that ice-breaking ridges are not disclosed in this embodiment.

Fig. 15 illustrates a seventh embodiment of the ice-breaking vessel according to the present invention. This sixth embodiment corresponds in general to the third embodiment described in connection with Figs. 5-10 above and will therefore not be discussed in detail in this connection.

The principal difference between this seventh embodiment and the second embodiment is that the first turnable propulsion device 71 and the second turnable propulsion device 72, with their respective propellers 75, are installed in parallel in a transverse direction of the monohull 2 at the second end 22 of the monohull 2 of the ice-breaking vessel 1, i.e. symmetrically with respect to the longitudinal centerline LCL.

The consequence of this positioning is that the advantages provided by the transversely non-aligned turnable propulsion devices described in connection with the first embodiment cannot be achieved.

However, all the benefits of the asymmetrically designed second end 22 of the monohull 2, also with a correspondingly designed first end 21 of the monohull 2, including the ice-contact areas, the ice-breaking ridges, as well as the asymmetrically vaulted portion, can nonetheless be achieved. Thus, this seventh embodiment provides for an advantageous result in less demanding circumstances.

The various modes of operation, i.e. the positioning of the turnable propulsion devices as described in connection with Figs. 1, 5 and 8-10, apply in principle to this fourth embodiment as well and are therefore not repeated in this connection.

This embodiment would be intended for the method of operating an icebreaking vessel in ice conditions as further defined in claims 10-13 and 15

In the above discussed embodiments, the monohull 2 is described including a longitudinal centerline LCL and a keel 23, which longitudinal centerline extends in the longitudinal direction of the monohull and which keel extends in the direction of the longitudinal centerline. As noted above, the longitudinal center-line would in these embodiments correspond to a keel line.

The monohull of the ice-breaking vessel can be without a clearly distinguishable keel in view of an optimal design for the intended operational circumstances.

On the other hand, if the monohull is configured with a keel, the keel can also be configures as discussed below in connection with Figs. 16-18.

Fig. 16 illustrates an eighth embodiment of the ice-breaking vessel according to the present invention. Fig. 17 illustrates a transverse vertical at section F-F as indicated in Fig. 16. This eighth embodiment corresponds in general to the third embodiment described in connection with Figs. 5-10 above and will therefore not be discussed in detail in this connection.

The principal difference between this eighth embodiment and the third embodiment is that the bottom 24 of the ice-breaking vessel 1 is provided with an asymmetric design towards midship. The waterline 5 at said ice-breaking draft is asymmetric, and so are the various waterlines indicated by thinner lines 51, 54 and 55 further towards midship of the vessel.

Furthermore, the keel 23 is also somewhat offset from the longitudinal center-line LCL, as indicated by distance h, and arranged at an angle a to the longitudinal centerline LCL, as shown in Fig. 16. The keel 23 is offset towards the side of the second ice-breaking ridge 82 and the second propulsion device 72 with respect to the longitudinal centerline LCL. Arranging the keel somewhat offset from the longitudinal centerline and at an angle to the longitudinal centerline may be used to improve the directional stability of the asymmetrically designed monohull of the ice-breaking vessel according to the present invention. Furthermore, this facilitates the flow of broken ice received and channeled by means of the asymmetric vaulted portion aftwards of the vessel as it moves forward in its travel direction.

In this eighth embodiment, the deck 3 is symmetrical. Clearly, the deck can be asymmetrical as discussed above in connection with the various embodiments.

Fig. 18 illustrates a ninth embodiment of the ice-breaking vessel according to the present invention. Fig. 17, discussed above in connection with Fig. 16, illustrates a transverse vertical at section F-F as indicated in Fig. 18. This ninth embodiment corresponds in principle to the fourth embodiment described in connection with Fig. 11 above and will therefore not be discussed in full detail in this connection.

Flowever, in Fig. 18 the ice-breaking vessel is shown in said first mode of operation, whereby the vessel moves with the first end 21 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field. This only illustrates the dual operational possibility of a vessel in which both ends are asymmetrically designed.

The principal difference between this ninth embodiment and the fourth embodiment is that the bottom 24 of the ice-breaking vessel 1 is provided with an asymmetric design towards midship from both ends, i.e. the first end 21 and the second end 22. The waterline 5 at said ice-breaking draft is asymmetric, and so are the various waterlines indicated by thinner lines 51,54 and 55 further towards midship, or the transverse center line TCL of the vessel.

Furthermore, the vessel is provided with a keel 23 extending towards both ends of the vessel. The keel 23 is somewhat offset from the longitudinal centerline LCL, as indicated by distance h, and arranged at an angle a to the longitudinal centerline LCL, on both sides of the transverse center line TCL.

The keel 23 is offset towards the side of the second ice-breaking ridge 82 and the second propulsion device 72 with respect to the longitudinal centerline LCL at the first end 21 of the monohull 2. In a corresponding manner the keel 23 is offset towards the side of the second ice-breaking ridge 82 and the fourth propulsion device 74 with respect to the longitudinal centerline LCL at the second end 22 of the monohull 2. The monohull 2 is symmetric with respect to the transverse centerline TCL.

Arranging the keel somewhat offset from the longitudinal centerline and at an angle to the longitudinal centerline may be used to improve the directional stability of the asymmetrically designed monohull of the ice-breaking vessel according to the present invention. Furthermore, this facilitates the flow of broken ice received and channeled by means of the asymmetric vaulted portion aftwards of the vessel as it moves forward in its travel direction. In this embodiment this advantage applies independently of in which direction the vessel moves, either with the first end 21 ahead or the second end ahead 22.

In this ninth embodiment, the deck 3 is symmetrical. Clearly, the deck can be asymmetrical as discussed above in connection with the various embodiments.

Providing an asymmetrical or symmetrical deck is mainly dependent on the overall design of the monohull 2 and can be chosen for any embodiment of the present invention in an optimal manner.

The keel arrangement discussed in connection with the eighth embodiment or the ninth embodiment can also be used in connection with the other corresponding embodiments of the present invention.

In general, the keel arrangement, as well as the above discussed ice-contact areas, ice-breaking ridges and the asymmetric vaulted portion, can be provided only at one of the first end or the second end of the monohull or both ends of the vessel, depending on the desired design of the vessel. Thus, the positioning of the turnable propulsion devices would be adapted accordingly.

In the above embodiments, when the ice-breaking vessel operates in said first mode of operation, with the first end 21 or the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field, the turnable propulsion devices in the travel direction towards the ice are described as being positioned so that the respective propellers are turned towards the ice, i.e. positioned in a pulling mode. Also the turnable propulsion devices at the other end in such a mode of operation are described in a pulling mode. However, the turnable propulsion devices can also be positioned in a pushing mode, i.e. with the propellers of the turnable propulsion devices being turned away from the travel direction.

In other words, it is clear that the propulsion devices with their propellers can be accommodated to the prevailing circumstances, as described for instance also in connection with Figs. 8-10. For various steering or directional purposes, the turnable propulsion devices can also be individually positioned as desired, and not only in the positions described in connection with Figs. 5 and 8- 10.

The ice-breaking vessel according to the present invention may additionally be provided with other propulsion devices, e.g. bow thrusters, tunnel thrusters, etc.

Figs. 19-21 illustrate a method of breaking ice according to the present invention, which deploys an ice-breaking vessel 1 comprising a monohull 2, which has a longitudinal centerline LCL, a first end 21 and a second end 22, a bottom 24 and a waterline, and which ice-breaking vessel is provided with propulsion devices (not shown in Figs. 19-21).

The embodiments of the present invention discussed above, as well as the method of operating an ice-breaking vessel, can realize the method of breaking ice according to the present invention that will be discussed in more detail for clarifying purposes in the following.

Figs. 19-21 correspond in principle to the embodiment of the present invention discussed in connection with Fig. 5 above, which illustrates an ice-breaking vessel 1 in a first mode of operation, in which it moves with the second end 22 ahead in a travel direction towards the ice, i.e. an ice formation or an ice field.

As shown in Fig. 19-21, the first ice-contact area 91 at the second end 22 is provided with a first ice-breaking ridge 81 and the second ice-contact area 92 at the second end 22 is provided with a second ice-breaking ridge 82.

The asymmetric design of the monohull, i.e. of the second end, provides for carrying out a phased ice-breaking method. The more forward part of the second end 22 of the monohull 2, including the first ice-contact area 91 with the first ice-breaking ridge 81, is engaged with the ice in a first phase IF cracking and splitting the ice and subsequently the more aftward part of the second end 22 of the monohull 2, including the second ice-contact area 92 with the second ice-breaking ridge 82, is engaged with the ice and finalizes the ice-breaking and pushes the ice away in a second phase IA.

As shown in Figs. 19-21 the ice in the ice-formation or ice-field is shown to be firstly split or cracked in the first phase IF (Fig. 19 and Fig. 20) and then the split or broken ice of the ice-formation or ice-field is shown to further broken up and mainly bent and pushed away or up and aside in the subsequent second phase IA (Fig. 19 and Fig. 21).

In Figs. 19-21, the engagement with the ice is shown to take place at the waterline 5 at said ice-breaking draft, indicated by section G-G in Fig. 7 and Fig. 19. In normal operation of the ice-breaking vessel 1, as well as in the icebreaking method according to the present invention, the vessel moves in a pitching mode, more or less, depending on the ice, sea and weather conditions. As a consequence, the engagement with the ice in said first phase and said second subsequent phase, takes place along the length of the first icebreaking ridge 81 and the second ice-breaking ridge 82 respectively, i.e. between sections G-G and H-H (Fig. 7 and 19). Thus, the first ice-breaking point 811 and the second ice-breaking point 821 are not in fixed positions. In other words, said ice-breaking draft is not constant.

However, for illustrative purposes, the first ice-breaking point 811 and the second ice-breaking point 821 are shown as being at fixed positions.

The ice-breaking vessel 1 is also provided with an asymmetric vaulted portion 10, as described above in connection with the various embodiments. The asymmetric vaulted portion 10 is arranged to extend in a longitudinal direction of the monohull 2 at said asymmetric waterline 5 at said ice-breaking draft between the first ice contact area 91 and the second ice-contact area 92 for receiving broken ice from the first phase and the subsequent second phase.

The asymmetric vaulted portion 10 receives and facilitates the removal of ice that has been broken by the ice-breaking vessel in the first phase and the subsequent second phase as discussed above. The broken ice is bent upwards towards a summit of the asymmetric vaulted portion 10 (Fig. 21).

Above the method of breaking ice according to the invention has been described in relation to the embodiment according to Fig. 5. However, the method can be carried out by means of the other embodiments described above as well.

Such a two-phased ice-breaking operation requires less propulsion power than a one-phased ice-breaking operation to achieve the same ice-breaking speed. Such a phased ice-breaking operation thus results in a lesser ice-breaking resistance.

The purpose of the above description is only to illustrate the basic idea of the present invention. The present invention may vary in detail within the scope of the ensuing claims.

Claims

An icebreaker vessel comprising a mono hull (2) having a longitudinal centerline (LCL), a first end (21) and a second end (22), a bottom (24) and a water boundary, wherein the icebreaker vessel (1) is provided with at least a first a pivoting propulsion device (71) and a second pivotable propulsion device (72), wherein the water boundary (5) is asymmetric with respect to the icebreaking draft of the mono body (2) at the first end (21) or at the second end (22); 2) a first ice contact region (91) is formed on a first side of the longitudinal centerline (LCL), a first distance from the first end (21) or the second end (22) and on the other side opposite to said first side of the longitudinal centerline (LCL); end (21) or one end (21) 22) a second ice contact area (92), and wherein the first pivoting actuator (71) is arranged adjacent the first ice contact area (91) and the second pivotable actuator (72) is arranged adjacent the second ice contact area (92).

An icebreaker vessel according to claim 1, characterized in that the first ice contact area (91) includes a first ice-breaking ridge (81) at a first distance from the first end (21) or the second end (22) and that the second ice contact area (92) is at a second distance a second ice-breaking ridge (82) at the first end (21) or the second end (22).

An icebreaker vessel according to claim 1, characterized in that the first end (21) and the second end (22) have an asymmetric vaulted portion (10) formed at the water boundary (5) at said icebreaking draft and arranged to extend the monoframe (2). in the longitudinal direction.

Icebreaker vessel according to Claim 1, characterized in that the asymmetrical vaulted portion (10) is arranged to extend longitudinally of the monoframe (2) between the first ice contact area (91) and the second ice contact area (92) at the first end (21) or at the second end (22). .

An icebreaker vessel according to claims 2 and 3, characterized in that the asymmetrical vaulted portion (10) is arranged to extend in the longitudinal direction of the monoframe (2) between the first icebreaker edge (81) and the second icebreaker edge (82) at the first end (21) or at the end (22).

An ice-breaker vessel according to claim 1 or 4, characterized in that the first pivoting power unit (71) and the second pivotable power unit (72) are arranged at different distances from the first end (21) or the second end (22).

An ice-breaker vessel according to claim 1 or 4, characterized in that the first pivoting power unit (71) and the second pivotable power unit (72) are arranged in parallel in the transverse direction of the mono body (2).

An ice-breaker vessel according to claim 1, characterized in that the monoframe (2) is provided with a keel (23).

An icebreaker vessel according to claim 8, characterized in that the keel (23) is arranged to the side of the longitudinal centerline (LCL) and at an angle (a) to the longitudinal centerline (LCL).

A method for operating an icebreaker vessel under ice conditions, the icebreaker vessel (1) having a mono hull (2) having a longitudinal centerline (LCL), a first end (21) and a second end (22), a bottom (24) and a water boundary; and wherein the icebreaker vessel (1) is provided with at least a first pivoting propulsion unit (71) and a second pivotable propulsion unit (72), wherein the icebreaker vessel uses a first end or a second end to break ice in the aforementioned ice conditions; at one end (21) or at the other end (22) a water limit (5) asymmetric to the ice fracture projection of the mono body (2) relative to the longitudinal centerline (LCL), characterized in that the mono body (2) is formed on the first side of the longitudinal line (LCL) (21) or the other end (22) a second ice contact area (91) and a second ice contact area (92) on a second side opposite to said first side of the longitudinal center line (LCL), at a second distance from the first end (21) or the second end, to provide a first pivotable drive unit (71) the ice contact area (91) and the second pivoting actuator (72) being arranged adjacent the second ice contact area (92), wherein the first ice contact area (91) is in contact with ice in a first step and the second ice contact area (92) is in contact with ice .

A method according to claim 10, characterized in that a first icebreaker ridge (81) is formed in the first ice contact region (91) and a second icebreaker ridge (82) is formed in the second ice contact region (92), wherein the first icebreaker ridge (81) with the first step and the second icebreaker brush (82) comes into contact with the ice in the subsequent second step.

A method according to claim 10 or 11, characterized in that an asymmetric vaulted portion (10) is formed between the ice contact areas or the ice breaking ridges, and wherein the asymmetric vaulted portion (10) receives shattered ice from the first stage or from the second stage.

Method according to claim 10 or 11, characterized in that, according to the method, the first reversible propulsion unit (71) assists in the icebreaking operation in the first step and the second rotary propulsion propulsion unit (72) assists in the icebreaking operation in the subsequent second step.

A method according to claim 13, characterized in that at least the first pivotable powertrain (71) and the second pivotable powertrain (72) are arranged at different distances from the first end (21) or the second end (22).

Method according to Claim 13, characterized in that at least the first pivoting power unit (71) and the second pivotable power unit (72) are arranged parallel to each other in the transverse direction of the mono body (2).

A method for breaking ice, which comprises using an ice-breaker platform (1) comprising a monolayer body (2) having a longitudinal centerline (LCL), a first end (21) and a second end (22), a bottom (24) and a water boundary, and wherein the icebreaker vessel (1) is provided with at least a first pivoting propulsion engine (71) and a second pivotable propulsion engine (72), characterized in that the ice breakage of the mono body (2) at the asymmetric waterline (5) a first ice contact area (91) on a first side and a second ice contact area (92) on a second side opposite to the first side of the longitudinal centerline (LCL) in a subsequent second step, wherein the first pivoting actuator (71) is provided in the first ice contact area 91) and the second pivoting drive unit (72) is arranged in connection with the second ice contact area (92).

A method according to claim 16, characterized in that a first ice-break region (91) is provided with a first ice-breaking ridge (81) for performing the first step and a second ice-breaking area (92) being formed with a second ice-breaking ridge (82).

Method according to claim 16 or 17, characterized in that said ice-breaking draft at said asymmetric water boundary (5) is provided between the first ice contact area (91) and the second ice contact area (92) to extend an asymmetric vaulted portion (10) the first step and the second step thereafter.