Dual cavity air lubrication system

Abstract

Disclosed is a dual cavity air lubrication system including an air flow splitter with an air inlet pipe branching into a first branch pipe and a second branch pipe, wherein a first passive valve is arranged in the first branch pipe and a second passive valve is arranged in the second branch pipe, wherein the branch pipes are in fluid communication with each other upstream from their respective valves, and wherein the valves are adapted for regulating the flow of air to respective air cavities to compensate for difference in air pressure in the cavities caused by a relative change in level of the cavities due to roll or heel of the vessel.

1 . Dual cavity air lubrication system ( 100 ) comprising:
 a first air cavity ( 54 - 59 ) and a second air cavity ( 54 ′- 59 ′) spaced apart therefrom, wherein said first and second air cavity are adapted for providing an air lubricating layer ( 9 ) between a substantially flat bottom ( 6 ) of the hull ( 4 ) of a vessel ( 1 ) and the water flowing under the flat bottom of the hull as said vessel is moving through the water;   an air flow splitter ( 101 ) comprising an air inlet pipe ( 102 ) which branches into a first branch pipe ( 110 ) which is connected to said first air cavity, and a second branch pipe ( 120 ) which is connected to said second air cavity;   an air compressor ( 80 ) connected to said air inlet pipe ( 102 ) for supplying air to both said first and second air cavity;   said system ( 100 ) further comprising:   a first passive valve ( 115 ) arranged in said first branch pipe ( 110 ), and a second passive valve ( 125 ) arranged in said second branch pipe ( 120 ), wherein said branch pipes are in fluid communication with each other upstream from their respective valves, and wherein said valves are adapted for regulating the flow of air to said air cavities to compensate for difference in air pressure between said cavities caused by a relative change in level of the cavities due to roll or heel of the vessel.   
     
     
         2 . The air lubrication system according to  claim 1 , wherein each valve ( 115 ,  125 ) is arranged at a distance (s 1 ,s 2 ), along the direction of flow from the air inlet pipe ( 102 ) to the branch pipe in which the valve is arranged, in the range of 0.2-2.5 m m from the point ( 104 ) where the air inlet pipe ( 102 ) branches into said branch pipe ( 110 ,  120 ). 
     
     
         3 . The air lubrication system according to  claim 1 , wherein said first and second valves are non-return valves or leaky non-return valves arranged for substantially blocking flow of air from the respective air cavities to the air inlet pipe. 
     
     
         4 . The air lubrication system according to  claim 1 , wherein said first and second valves are pressure-differential regulator valves adapted for causing a predetermined substantially constant pressure drop across the valve. 
     
     
         5 . The air lubrication system according to  claim 1 , wherein each of said valves is adapted for regulating a pressure drop its respective branch pipe such that there is a pressure drop of at least 20 mbar, from an inlet side of said valve to an outlet side of said valve when the compressor supplies air to said air inlet pipe to generate the air lubricating layer. 
     
     
         6 . The air lubrication system according to  claim 1 , wherein said first and second valve are each biased towards allowing flow of air through said valve in a downstream direction of its respective branch pipe and against allowing flow of air through said valve in the opposite direction. 
     
     
         7 . The air lubrication system according to  claim 1 , wherein said first and second branch pipe each comprise a restricted pipe section ( 112 ;  122 ) having a smaller cross-sectional flow area than said air inlet pipe ( 102 ), wherein said first passive valve ( 115 ) is arranged in the first restricted pipe section ( 112 ) and said second passive valve ( 125 ) is arranged in the second restricted pipe section ( 122 ). 
     
     
         8 . The air lubrication system according to  claim 7 , wherein said first and second branch pipe ( 110 ;  120 ) each further comprise an outlet section ( 117 ;  127 ) downstream from its restricted section ( 112 ;  122 ) and connected thereto and having a larger cross-sectional flow area than said restricted section ( 112 ;  122 ). 
     
     
         9 . The air lubrication system according to  claim 8 , wherein said cross-sectional flow area of said first and/or second outlet section ( 117 ;  127 ) is smaller than that of the air inlet pipe ( 101 ). 
     
     
         10 . The air lubrication system according to  claim 7 , wherein the cross-sectional flow area of said first and/or second restricted pipe section ( 112 ;  122 ) is smaller by a factor  3  or more than that of the air inlet pipe. 
     
     
         11 . The air lubrication system according to  claim 7 , wherein said first and second branch pipe ( 110 ;  120 ) each further comprise a pipe section which extends from said air inlet pipe to the respective restricted section, said pipe section having a larger cross-sectional flow area than said restricted section. 
     
     
         12 . The air lubrication system according to  claim 7 , wherein the restricted section of each branch pipe is arranged at distance of less than 5 m from the connection of said branch pipe to its corresponding air cavity. 
     
     
         13 . The air lubrication system according to  claim 7 , wherein the cross-sectional flow area of said branch pipes ( 110 ;  120 ) and/or said restricted sections ( 112 ,  122 ) thereof has a circular contour. 
     
     
         14 . The air lubrication system according to  claim 1 , further comprising an adjustable valve ( 103 ) in said air inlet pipe ( 102 ). 
     
     
         15 . The air lubrication system according to  claim 1 , wherein said first branch pipe ( 110 ) and said second branch pipe ( 120 ) each have a length of less than 10 m from their end proximate to the air splitter section to the ends connected to their respective air cavity. 
     
     
         16 . The air lubrication system according to  claim 1 , wherein said first and second air cavity each comprise:
 sidewalls ( 71 , 71 ′) and a top wall ( 72 ) defining said cavity with an opening ( 73 ) situated in an interface plane ( 76 ) that is transversal to the sidewalls ( 71 , 71 ′), the opening ( 73 ) having a front end ( 74 ) and a rear end ( 75 ) seen in the length direction of the cavity, an air inlet port ( 77 ) spaced from the opening ( 73 ) and connected to one of said branch pipes ( 110 , 120 ) for introducing air into the cavity, wherein the length of the opening ( 73 ) of the cavity is between 2 and 10 m, and the distance of the top wall ( 72 ) from the interface plane ( 76 ) is between 0.2 m and 0.5 m.   
     
     
         17 . The air lubrication system according to  claim 1 , wherein said air compressor is the only air compressor ( 80 ) that is connected to said air inlet pipe ( 102 ) for supplying air to both said first and second air cavity. 
     
     
         18 . Vessel ( 1 ) comprising a hull ( 4 ) having a center line ( 50 ), opposing sides ( 51 , 52 ) and a substantially flat bottom ( 6 ), the vessel having a number of air lubricating systems according to  claim 1 , wherein the air cavities of the air lubricating systems debouch in the flat bottom ( 6 ). 
     
     
         19 . Vessel according to  claim 18 , wherein said cavities each have a length (Lc), a distance of the top wall ( 19 ) from the interface plane ( 30 ) (Hc) and a width (W), wherein the ratio Lc/Hc is in the range of 7:1 to 13:1, the ratio W/H is in the range of 1.3:1 to 2.5:1 and the ratio Lc/W is in the range of 3.5 to 1 to 7:1. 
     
     
         20 . Vessel according to  claim 18 , wherein said first and second air cavity of one or more of said dual cavity air lubricating systems are arranged adjacent to each other along the width of the hull ( 4 ) and at the same distance to the flat bottom ( 6 ). 
     
     
         21 . Vessel according to  claim 18 , wherein the vessel accommodates said first and said second air cavities of each of said air lubricating systems on opposite sides of the center line at a predetermined length position. 
     
     
         22 . Vessel according to  claim 18 , wherein the vessel accommodates said first and said second air cavities of each of said air lubricating systems on a same side of the center line at a predetermined length position, and wherein in each of said air lubricating systems said first air cavity neighbours said second air cavity.