Background Art As well known to those skilled in the art, ballast tanks are provided in a vessel to ballast the vessel and to minimize a variation in the gravity center of the vessel during a loading or unloading work and to accomplish desired draft and stability of the vessel during a voyage. In the prior art, a plurality of ballast tanks are symmetrically arranged at the left and right-hand sides of a vessel while being completely isolated from each other so as to prevent ballast seawater from moving between the tanks.

When a vessel is fully loaded with freight, the gravity center of the vessel descends to a desired position under the seawater level even though the ballast tanks are kept empty. In such a case, it is possible for the vessel to accomplish desired draft and stability while voyaging on the sea regardless of external impact, such as wave force, acting on the vessel during the voyage. However, when a vessel voyages without freight, it is necessary to ballast the vessel with seawater received into the ballast tanks before the voyage. Due to the ballast seawater within the ballast tanks, the gravity center of the vessel descends to a desired

position and allows the vessel to accomplish desired draft and stability.

Therefore, it is necessary to discharge ballast seawater from the ballast tanks when a vessel is loaded with freight and to receive ballast seawater into the tanks when the freight is unloaded. Such a freight loading and unloading work is repeatedly performed, and so it is necessary to repeatedly discharge and receive ballast seawater from and into the ballast tanks. When ballast seawater is newly received into the ballast tanks, a variety of sediments, such as mud, microorganisms and solid impurities, are introduced into the tanks along with seawater and float in water within the tanks, and are finally deposited on the bottoms of the tanks. Such deposited sediments are not naturally removed from the ballast tanks even though the tanks are repeatedly emptied, but the quantity of deposited sediments on the bottoms of the tanks is gradually increased since ballast seawater is repeatedly received into the tanks.

Such a deposition of sediments on the bottoms of ballast tanks is influenced by the conditions of a specified sea area at which the vessel is ballasted with seawater. That is, the quantity of inlet sediments is exceedingly increased when ballast seawater is received into the ballast tanks at a shallow sea area, a specified sea area having plenty of mud, silt, shale, silica and/or fine sand on the sea bed, or a specified sea area having a red tide or a high concentration of sea microorganisms, such as green algae. Particularly, mud-based sediments, deposited on the bottoms of the ballast tanks, are gradually hardened as time elapses since mud typically repels water and easily becomes dense under pressure.

It is very difficult to remove such hardened, mud-based sediments from the ballast tanks.

In the prior art, workers have to enter the ballast tanks to reach the bottoms prior to manually removing such deposited sediments from the bottoms through a water blasting process.

When the ballast tanks of a vessel contain ballast seawater, the water repellent rate between particles within the deposited sediments is significantly lower than that when the ballast tanks are emptied. The interparticle locking force of the sediments is thus somewhat less when the tanks contain water, and so

the deposited sediments may be easily, manually removed from the bottoms of the tanks through a water blasting process at a time just after the tanks are emptied.

However, such a conventional manual water blasting process is problematic in that it is very difficult for workers to repeatedly wash the ballast tanks to remove the sediments from the tanks before every voyage. In addition, the manual water blasting process may undesirably allow some sediment to remain on the bottoms of the tanks without being covered with water. In such a case, the interparticle water is removed from the sediments as time elapses, thus enforcing the interparticle water repelling action and strengthening the interparticle locking force. It is thus very difficult to remove such hardened sediments through a water blasting process.

In addition, a biological slime is formed on the bottom and sidewalls of each ballast tank due to the microorganisms, and so it is very dangerous for workers to work within the tanks since the workers may slip on the slippery bottoms of the tanks and may encounter safety hazards while working within the tanks.

Disclosure of the Invention Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus for removing sediments from the ballast tanks of vessels, which is designed to eject cleaning seawater under constant pressure onto the bottom of a ballast tank for a predetermined time while or before emptying the ballast tank, thus allowing a variety of sediments, such as mud, microorganisms and/or solid impurities, to float in the ballast seawater within the tank and effectively removing the sediments from the tanks when discharging the ballast seawater, and which effectively prevents a corrosion of the bottom and sidewalls of the tank and conserves labor while removing such sediments from the tanks in addition to a reduction in its maintenance cost.

In order to accomplish the above object, the present invention provides an apparatus for removing sediments from ballast tanks of a vessel, comprising a main supply pipe connected to a seawater inlet pipe through a water pump installed

within a fire room of the vessel so as to receive cleaning seawater from the seawater inlet pipe using a pumping force of the pump. A plurality of sub-supply pipes are branched from the main supply pipe and receive the seawater from the main supply pipe, with a valve being installed on each of the sub-supply pipes. A seawater ejection pipe extends from each of the sub-supply pipes into a ballast tank and ejects the cleaning seawater under pressure into the ballast tank under the control of the valve. A plurality of ejection nozzles are formed on the ejection pipe at positions between the reinforcing ribs arrayed on the bottom of the ballast tank.

In the above apparatus, each of the ejection nozzles preferably has a diameter of 0.1 mm mm. In addition, it is preferable to set the number of ejection nozzles of each of the ejection pipes to l ~ 7.

The apparatus of this invention ejects cleaning seawater under pressure onto the bottom of a ballast tank, thus allowing a variety of sediments to float in seawater within the tank and effectively removing the sediments from the tanks when discharging the seawater.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of a vessel, showing a sediment removing apparatus installed within the vessel in accordance with the preferred embodiment of the present invention; Fig. 2 is a sectional view of the vessel of Fig. 1, showing a water ejection pipe included in the sediment removing apparatus of this invention; Fig. 3 is a perspective view of a part of the water ejection pipe included in the apparatus of this invention; and Fig. 4 is a sectional view of the water ejection pipe of Fig. 3.

Best Mode for Carrying Out the Invention Fig. I is a schematic view of a vessel, showing a sediment removing apparatus installed within the vessel in accordance with the preferred embodiment of the present invention. This drawing particularly shows an arrangement of cleaning seawater ejection pipes, designed to lead cleaning seawater from a seawater inlet port and eject the seawater under pressure into the ballast tanks.

Fig. 2 is a sectional view of the above vessel, showing the sediment removing apparatus of this invention with a cleaning seawater ejection pipe connected to left and right-hand ballast tanks. Fig. 3 is a perspective view of a part of the seawater ejection pipe of this invention, showing the pipe extending across the reinforcing ribs of a ballast tank and the position of the cleaning seawater ejection nozzles relative to the ribs. Fig. 4 is a sectional view of the water ejection pipe of Fig. 3, showing the direction of the water ejection nozzle.

As shown in the drawings, the apparatus for removing sediments from the ballast tanks 1 and 1'of a vessel"S"comprises a main supply pipe 4 linearly extending through the gallery between the two rows of ballast tanks 1 and 1', with a plurality of sub-supply pipes 5 and 5'extending from the main supply pipe 4.

The main supply pipe 4 is connected to a seawater inlet pipe 2 through a water pump 8 installed within the fire room 8 of the vessel"S"and supplies cleaning seawater from the seawater inlet pipe 2 into the sub-supply pipes 5 and 5'using the pumping force of the water pump 3. A valve 6 or 6'is installed on each of the sub-supply pipes 5 and 5', while a seawater ejection pipe 7 or 7', having a plurality of ejection nozzles 11 and 11', extends from the outside end of each sub-supply pipe 5 or 5'. The ejection nozzles 11 and 11'of each of the water ejection pipes 7 and 7'are positioned between the reinforcing ribs 9 and 9'regularly arrayed on the bottom 10 of a ballast tank 1 or 1'. In the present invention, each of the ejection nozzles 11 and 11'has a diameter of 0.1 mm mm. In addition, it is preferable to set the number of ejection nozzles of each of the ejection pipes to 1- 7.

The amount of ballast seawater within the ballast tanks 1 and 1'has to be

controlled in a conventional manner so as to accomplish a desired position of gravity center of the vessel"S"or to appropriately ballast the vessel"S"to provide desired draft and safety of the vessel"S"in accordance with the weight of loaded freight of the vessel"S". When it is desired to discharge ballast seawater from the ballast tanks 1 and 1', the sediment removing apparatus of this invention starts its operation as follows to float the sediments in the ballast seawater within the tanks I and 1'and to remove the sediments from the tanks 1 and 1'along with discharged ballast seawater. That is, the apparatus primarily feeds cleaning seawater under pressure from the seawater inlet pipe 2 into the main supply pipe 4 using the pumping force of the water pump 3 of the fire room 8. The cleaning seawater is, thereafter, fed from the main supply pipe 4 into the sub-supply pipes 5 and 5'and is ejected from the sub-supply pipes 5 and 5'into the tanks 1 and 1' under the control of the valves 6 and 6'mounted on the sub-supply pipes 5 and 5'.

In such a case, the cleaning seawater ejection process for the ballast tanks 1 and 1' is continued for a desired period of time, preferably, several seconds to several minutes. Of course, it should be understood that the cleaning seawater ejection process for the ballast tanks 1 and 1'may be continued for several minutes to several ten minutes as desired under the control of the valves 6 and 6'.

Within each of the ballast tanks 1 and 1', a water ejection pipe 7 or 7'is branched from an associated sub-supply pipe 5 or 5', with a plurality of water ejection nozzles 11 and 11'regularly formed on the water ejection pipe 7 or 7'.

In the present invention, it is necessary to appropriately set the interval, the number and the ejection angles of the nozzles 11 and 11'in accordance with the reinforcing ribs 9 and 9'arrayed on the bottom 10 of the vessel 10, thus allowing the vortexes formed by the ejected seawater from the nozzles 11 and 11'to effectively act on the bottom 10 without interfering with any rib 9 or 9'.

In order to allow the deposited sediments to float in the ballast seawater within the ballast tanks by the vortexes caused by the ejected cleaning seawater, it is necessary to set the flow velocity of the seawater on the bottom 10 of the tanks 1 and 1'to a level of higher than the critical shear velocity of the deposited sediments. Therefore, the sediment removing apparatus of this invention has to

be designed to eject a sufficient quantity of cleaning seawater onto the bottom of each of the ballast tanks 1 and 1'at a high speed to form a desired flow velocity of higher than the critical shear velocity of the deposited sediments on the bottom 10 of each tank 1 or 1'.

In the present invention, the cleaning seawater ejection process of the sediment removing apparatus for accomplishing the removal of deposited sediments from the ballast tanks 1 and 1'may be effectively performed while the tanks 1 and 1'contain ballast seawater, at a time when ballast seawater is being newly received or discharged into or from the tanks 1 and 1', or after the tanks 1 and 1'are completely emptied. However, in the case of empty ballast tanks 1 and 1', the water repelling action of the deposited sediments on the bottoms of the empty tanks is enforced and allows the sediments to be more hardened.

Therefore, it is better to perform the cleaning seawater ejection process of the apparatus while discharging the ballast seawater from the tanks 1 and 1'and before completely discharging the ballast seawater from the tanks 1 and 1'.

In the apparatus of this invention, the height of the seawater ejection nozzles 11 and 11'of the ejection pipes 7 and 7'above the bottom 10 of the ballast tanks 1 and 1'is an important factor, which determines the effective cleaning seawater ejection angles, the quantity of ejected cleaning seawater, and the cleaning seawater ejection velocity of the nozzles 11 and 11'. When the ejection pipes 7 and 7'are fixedly supported on the reinforcing ribs 9 on the bottom of the tanks 1 and 1', it is possible to preferably reduce the installation cost of the apparatus. However, it should be understood that the height of the ejection pipes 7 and 7'above the bottom of the tanks 1 and 1'may be somewhat freely changed as desired.

Industrial Applicability As described above, the present invention provides an apparatus for removing sediments from the ballast tanks of vessels. This apparatus ejects cleaning seawater under constant pressure onto the bottom of each ballast tank for

a predetermined time while or before completely emptying the ballast tank, thus allowing a variety of sediments, such as mud, microorganisms and/or solid impurities, to float in ballast seawater within the tank and effectively removing the sediments from the tank when discharging the ballast seawater. The apparatus of this invention thus performs an automatic sediment removing process different from a conventional manual water blasting process, thus conserving labor while removing the sediments from the ballast tanks. It is possible to frequently remove sediments from the ballast tanks using the apparatus of this invention before the sediments are hardened, and so the apparatus effectively prevents a corrosion of the bottom and sidewalls of the tanks. The apparatus of this invention is also mechanically operated, thus being easily and simply operated while being reduced in its maintenance cost. The sediment removing apparatus of this invention is effectively used in middle or large-sized vessels regardless of types of the vessels and desirably removes sediments from the ballast tanks of such vessels.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.