Air lubrication system

Abstract

A system for providing an air lubricating layer between a substantially flat bottom (3) of a vessel (1) and the water flowing under the bottom as the vessel is moving through the water, whereby the system includes sidewalls (5,5) and a top wall (4) defining a cavity (6) with an opening (13) situated in an interface plane that is transversal to the sidewalls (5,5), at the level of the flat bottom (3), the opening having a front end (9) and a rear end (15) seen in the length direction of the cavity, an air inlet (10) spaced from the opening for introducing air into the cavity, whereby the length of the opening (13) of the cavity (6) is between 2 and 10 m and the distance (H) of the top wall (4) from the interface plane is between 0.2 m and 0.5 m.

Claims

1. A system for providing an air lubricating layer between a substantially flat bottom of a vessel and water flowing under the substantially flat bottom as the vessel is moving through the water, the system comprising: sidewalls; a top wall defining a cavity with an opening defining an interface plane located at a distance from the top wall, substantially at a level of the substantially flat bottom, the opening having a front end and a rear end configured to be seen in a direction of forward movement of the vessel; an air inlet separate from the opening configured for introducing air into the cavity; and at least one wave deflecting member extending inside the cavity in a width direction, at a distance from the interface plane, the wave deflecting member being fixed to the side walls and/or top wall and being oriented substantially transversely to the interface plane.

2. The system according to claim 1, the at least one wave deflecting member is curved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Some embodiments of a system for providing an air lubricating layer between the hull of a vessel and the water flowing under the hull as the vessel is moving through the water according to the present invention will by way of example be described in detail with reference to the accompanying drawings. In the drawings:

(2) FIG. 1 shows a schematic side view of a vessel which as an example comprises two cavities arranged after each other in the hull of the vessel,

(3) FIG. 2 shows a bottom view of the vessel,

(4) FIG. 3 shows a schematic side view of system according to the invention having curved wave deflecting members extending transversely in the cavity,

(5) FIG. 4 shows a schematic side view of system according to the invention having substantially plane wave deflecting members extending transversely in the cavity,

(6) FIG. 5 shows a schematic view of the opening of a cavity, seen from the bottom of the vessel.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a schematic side of a vessel 1 according to the invention having a hull 2 and a bottom surface 3. The hull 2 has a length Lh of for instance between 50 m and 400 m, measured along the bottom surface 3.

(8) As shown in FIG. 2 the bottom surface 3 of the vessel 1 comprises two rows of cavities 6, each having five cavities 6.1a to 6.1e and 6.2a to 6.2e arranged next to each another across the width Wv of the vessel. The width Wv may be between 10 and 50 m, for instance between 15 m and 20 m. The rows are shown as having a general V-shape, but the cavities could also be arranged on a straight of curved line, or in any other pattern. The number of cavities is selected according to the width Wv of the bottom surface 3. It is, however, also possible to have a single cavity in the bottom surface 3.

(9) The cavities preferable all have the same dimensions, but they could also have different dimension, for example the cavities near the side of the vessel could have a different shape and/or size.

(10) FIGS. 3-5 shows a cavity 6 having a front end 9, a rear end 15, a top wall 4, a rear wall 16, two side walls 5, 5, and an air inlet 10, an air supply duct 11 connected to the air inlet 10. The cavity 6 further comprises an opening 13 which is substantially flush with bottom surface 3 of the hull. The opening 13 has a length Lc which is relatively short compared the vessel length Lh and which lies between 2 m and 10 m. The width W of the opening 13 (see FIG. 5) is preferable between 0.5 m and 1.5 m. The cavity has a height H, measured from the bottom surface 3 to a top wall 4, which may be between 0.2 m and for instance 0.5 m.

(11) Other small size cavities having a length Lc between 1.5 m and 5 m at a height H of between 0.2 m and 1.5 m, preferably 0.2 m and 1 m also provide an efficient and stable air lubricating layer.

(12) Near a front end 9 of the cavity 6, an air inlet 10 is provided, which is connected to an air supply duct 11. A compressor 12 takes in atmospheric air through a duct 11 and supplies compressed air to the cavity 6 in order to expel water from the cavity. A controller 20, such as a computer device, is connected to the compressor 12 for operating the compressor depending on the speed of the vessel.

(13) When the vessel is sailing through the water the moving water across the water-air interface in the cavity 6 results in a Kelvin Helmholtz Instability and forms small-sized bubbles 14. These bubbles escape via a bubble outflow region at the rear end 15 of the cavity 6. At the rear end 15, the cavity 6 has a downwardly sloping surface, forming a wedge-shaped space near the rear 15 of the cavity. From this outflow region, the bubbles 14 spread towards the aft 18 of the hull 2, to cover a majority of the bottom surface 3. The downwardly sloping surface can be formed as straight wall 16, or as a curved wall 16. The preferred embodiment of FIG. 3 shows a curved rear wall 16 which at the position 15 of the bottom surface 3 is tangent with said bottom surface 3. In order for the bubbles to be guided smoothly out of the cavity it is sufficient that the lower part of the rear wall 16 is curved or inclined. For a smooth transition of the bubbles from the cavity is important the rear wall 16 extends all the way to the position 15 of the bottom surface 3. It is not necessary that the portion of the rear wall 16 being adjacent the top wall 4 is curved or inclined. This portion of the rear wall 16 could, for example, be vertical.

(14) As shown in FIGS. 3 and 4, a number of wave deflecting members 7, 7, 7 extends transversely inside the cavity 6. These wave deflecting members stay clear from the top wall 4 and/or side walls 5, 5for allowing a free flow of air through the cavity. Alternatively, the wave deflecting members extend to the top wall 4 and/or side walls 5,5 but are transparent for air, for instance by being provided with perforations, or forming a mesh like pattern. These wave deflecting members 7, 7, 7 facilitate the starting-up of the system. Before the system is activated the cavity 6 will normally be full of water. The wave deflecting members 7, 7, 7 serve to deflect the waves emerging from the front end 9 of the cavity 6 when the vessel in moving forward through the water, and the turbulence generated there from will be deflected whereby less air will be drawn out of the cavity 6 during the initial startup of the system. A single wave deflecting member 7 might be sufficient in some instances, whereas an improved effect is obtained by providing more wave deflecting members, such as 3 or 5, or more than 5. The wave deflecting member(s) can be fixed to the sidewalls 5, 5 and/or to the top wall 4.

(15) The at least one wave deflecting member 7 can be curved, or it can be formed by a substantially plane element arranged vertically, or at an inclined angle, such that it sloped towards the aft 18 of the hull 2 in a downward direction. The members 7, 7, 7 can be solid or, optionally, be provided with holes or openings extending from a front to a rear side of a member 7, 7, 7.