Patent Publication Number: US-2010107949-A1

Title: Multi-purpose icebreaker

Description:
FIELD OF THE INVENTION 
     The present invention relates to a multi-purpose icebreaker having a front part, an aft part, main propulsion devices and steering devices. 
     PRIOR ART 
     The conventional icebreakers are provided with shaft propellers and rudders at the stern of the vessel. In order to increase power for ice breaking the shaft propellers were added also in the front of the vessel. 
     In the first multi-purpose icebreakers the shaft propellers and rudders at the stern of the vessel have been substituted by azimuth propellers, which essentially improved the steering characteristics of the ship. Therefore in the front of the vessel it was necessary to provide only with several steering tunnel thrusters. 
     Many different modifications have been presented for improving icebreaking vessels. The document U.S. Pat. No. 5,218,917 presents a special icebreaking ship, which has azimuth propellers at the stern of the ship. The special feature of this vessel is that only the aft part of the ship is optimized for braking ice and the forward part of the ship is optimized for open water conditions. The purpose of this is that normally in open water the ship is moving forward and in heavy ice conditions the ship is breaking ice by moving in the aft direction. 
     The document U.S. Pat. No. 5,996,520 presents an icebreaking ship having azimuth propellers at the both ends of the ship. Because of the characteristics of the azimuth propellers the ship is easily capable to move into any direction. The special feature of this vessel is that the hull of the ship is specially designed to move sideward, which means slightly a side against the ice field. The purpose of that is to make into the ice field a passage, which is wider than the breadth of the ship. 
     An object of the present invention is to provide an improved multi-purpose icebreaker. The second purpose of the invention is to provide a multi-purpose icebreaker, which has improved steering characteristics and which is efficient at continuous slow speed in heavy ice conditions, especially when ice ridges may occur. 
     SUMMARY OF THE INVENTION 
     The features of the invention are described in the characterizing part of claim  1 . The icebreaker according to the invention is characterized in that in the multi-purpose icebreaker at least one main propulsion device is located in the front part of the vessel and at least one steering device is located in the aft part of the vessel. 
     The benefit of the arrangement is that this kind of icebreaking vessel has excellent steering characteristics. By using the main azimuth propulsion devices located at the bow of the ship, the vessel can easily turn to any direction. The icebreaking vessel can push the ice field efficiently forward and also to both sides if for example the passage has to be made wider for the ship towed. 
     The icebreaking ship provided with azimuth propulsion devices at the front part of the ship is especially useful in the situations, where the ship has to move slowly in the in heavy ice conditions, and when ramming is not possible. These characteristics are also useful, when the ship has to stay at a predetermined position in a moving ice field. Such needs occur for example on the oil fields at arctic seas. 
     According to a preferred embodiment of the invention the multi-purpose icebreaker has in the front part of vessel two main propulsion devices, which are azimuth propulsion devices, and in the aft part of the vessel the steering device comprises one or more tunnel thrusters. 
     According to a second preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of vessel comprises two azimuth propulsion devices, and that the steering device in the aft part of the vessel comprises one or more azimuth propulsion devices, which are smaller than the main propulsion devices in the front part of the ship. 
     According to a third preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of the vessel comprises two conventional shaft propulsion devices, and the steering device in the aft part of the vessel comprises one or more azimuth propulsion devices. 
     According to a fourth preferred embodiment of the invention in the multi-purpose icebreaker the main propulsion device in the front part of the vessel comprises two conventional shaft propulsion devices, and the steering device in the aft part of the vessel comprises one or more tunnel thrusters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in the following by means of an example, with reference to the appended drawings in which 
         FIG. 1  presents a side view of an embodiment of the multi-purpose icebreaker according to the invention. 
         FIG. 2  presents a side view of the second embodiment of the multi-purpose icebreaker according to the invention. 
         FIG. 3  presents a side view of the third embodiment of the multi-purpose icebreaker according to the invention. 
         FIG. 4  presents a side view of the multi-purpose icebreaker of  FIG. 1  attached to a turret and operating as an offloading icebreaker on an oil field under the sea 
         FIG. 5  presents a bottom view of an embodiment of the multi-purpose icebreaker according to the invention. 
     
    
    
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  presents a multi-purpose icebreaker  10  being attached to another ship  11 . The purpose of the attachment is for example that the icebreaker  10  is towing the other ship  11 . However, the attachment may be for other reasons, as described below. 
     In  FIG. 1  the water  12  is described as open water, but of course because the vessel  10  is an icebreaker, there may be also solid ice or ice ridges on the surface of the water  12 . 
     The multi-purpose icebreaker  10  in  FIG. 1  is provided with two azimuth propulsion devices  20  at the bow of the vessel. These azimuth propulsion devices  20  provide the only propulsion thrust for the vessel  10 . For improving steering in difficult circumstances and for dynamic positioning the multi-purpose icebreaker  10  is also provided with three steering tunnel thrusters  21  at the stern of the vessel. 
     An advantage of the pulling mode azimuth propulsion devices  20  at the bow of the icebreaker  10  of  FIG. 1  is that it is very easy to steer the icebreaker in the heavy ice conditions. The icebreaker  10  can easily make turns and it can be steered for widening the breadth of the required channel to be formed in the ice. 
     The propulsion devices  20  at the bow of the icebreaker  10  also give very good characteristics for the vessel when it is needed to move forward continuously at slow speed and ramming is not possible. The presented icebreaker  10  can push through the solid ice and ice ridges. 
     The second advantage of the propulsion devices  20  at the bow of the icebreaker  10  of  FIG. 1  is that the propellers in front of the vessel crush the ice blocks smaller. Then the ice blocks do not disturb the other vessel to be towed or some other equipment close the vessel, as described below. 
       FIG. 2  presents the second embodiment of the multi-purpose icebreaker  10  according to the invention. The icebreaker  10  is also attached to another ship  11  for towing or other purpose. In  FIG. 2  the icebreaker  10  is also provided with two azimuth propulsion devices  20  at the bow of the vessel. In this embodiment of the icebreaker  10  these azimuth propulsion devices  20  are not the only propulsion apparatuses of the vessel  10 , but they provide the main propulsion thrust for the icebreaker  10 . 
     The difference of the icebreaker  10  of  FIG. 2  compared to the icebreaker  10  of  FIG. 1  is that in  FIG. 2  the icebreaker  10  is provided with two smaller azimuth thrusters  22  at the stern of the vessel  10 . The azimuth thrusters  22  are mainly intended for improving steering in difficult circumstances and for dynamic positioning. However, they can also be used for forward thrust together with the main azimuth propulsion devices  20  at the bow of the vessel, so increasing the total forward thrust of the icebreaker  10 . 
     In  FIG. 3  there is described the third embodiment of the multi-purpose icebreaker  10  according to the invention. This icebreaker  10  is provided with conventional shaft propellers  30  in front of the vessel. These shaft propellers  30  provide the main forward thrust for the vessel  10 . In order to improve steering the multi-purpose icebreaker  10  is provided with three steering tunnel thrusters  21  at the bow of the vessel and with two smaller azimuth thrusters  22  at the stern of the vessel  10 . 
     The small azimuth thrusters  22  at the stern of the vessel  10  are mainly intended for improving steering in difficult circumstances and for dynamic positioning. However, as described in  FIG. 2 , they can also be used for increasing forward thrust together with the conventional shaft propellers  30 , which are the main propulsion devices of the icebreaker  10 . 
       FIG. 4  presents the multi-purpose icebreaker  10  of  FIG. 1  provided with a turret  40  for loading oil to the tanker vessel  11  attached to the icebreaker  10 . In  FIG. 4  the turret  40  is provided with oil tubes  41  and anchor wires  42 . In this case the azimuth propulsion devices  20  at the bow of the icebreaker  10  are very useful because they keep the turret  40 , oil tubes  41  and anchor wires  42  clear from ice. The propellers of the azimuth propulsion devices  20  also crush the large ice blocks smaller. 
       FIG. 5  presents a bottom view of a multi-purpose icebreaker  10  according to the invention. According to  FIG. 1  the icebreaker  10  is provided with an inward curved towing notch  15 , two azimuth propulsion devices  20   a  and  20   b  at the bow of the vessel, and three steering tunnel thrusters  21  at the stern of the vessel. In the bottom of the icebreaker  10  the turret  40  is located in the middle of the ice plough  16 , so that the ice plough  16  forms a protecting shelter around the turret  40 . In  FIG. 5  it can be clearly seen the protective function of the ice plough  16 . The azimuth propulsion devices  20   a  and  20   b  at the bow of the vessel  10  push the ice blocks along the sides of the ice plough  16 , so preventing the ice blocks from striking the turret  40  or the equipment, such as the oil tubes  41  and anchoring wires  42  attached to the turret  40 . 
     It is obvious to a person skilled in the art that the different embodiments of the invention may vary within the scope of the claims presented below. 
     REFERENCE NUMERALS 
       10  Multi-purpose icebreaker 
       11  Vessel 
       12  Water 
       15  Towing notch 
       16  Ice plough 
       20  Main azimuth propulsion device 
       21  Steering tunnel thruster 
       22  Smaller azimuth propulsion device 
       30  Conventional shaft propeller 
       40  Turret 
       41  Oil tube 
       42  Anchor wire