Air lubrication system with blowing time control

Abstract

Provided is an air lubrication system that appropriately controls the air blowing time without complicating the configuration, suppresses the power required for air blowing, and improves the effect of reducing frictional resistance. [Solution] An air lubrication system that intermittently blows air onto the bottom 1A of a ship 1 to reduce the frictional resistance of the hull, and is equipped with an air outlet 10 provided on the bottom 1A of the ship, a ship speed detection means 20 that detects the ship speed of the ship 1, and a control means 30 that controls the blowing time of the air intermittently blown out from the air outlet 10 based on the set air blowing flow rate and air blowing width blown out from the air outlet 10 and the ship speed.

Description

[Technical Field]

[0001] The present invention relates to an air lubrication system that reduces frictional resistance of a ship's hull by blowing air onto the ship's bottom, forming bubbles that cover the bottom. [Background technology]

[0002] In air lubrication systems for ship hulls, it is known that the reduction in frictional resistance increases in proportion to the equivalent air film thickness (ta), which is the thickness of the air film when it is assumed that the air blown out onto the bottom of the ship exists as a film. Patent Document 1 also discloses a hull friction resistance reduction device that is equipped with an automatic air distribution device that automatically distributes air by blowing air from multiple air outlets onto the bottom of the ship while switching between the multiple air outlets, and arranges n air outlets with predetermined widths across the width of the hull in n divisions according to the width of the bottom of the ship, and the automatic air distribution device blows air from all of the multiple air outlets in one air blowing cycle while switching between the air outlets that blow out air from among the multiple air outlets in a predetermined order. Patent Document 2 also discloses a hull friction resistance reduction system that includes a fluid monitoring device that monitors the fluid around the bottom of the ship and has a signal processing unit that processes signals detected by multiple piezoelectric ultrasonic probes fixed to the bottom of the ship, and a bubble ejection mechanism that ejects bubbles toward the bottom of the ship, in which the signal processing unit analyzes ultrasonic echo signals based on the signals from the ultrasonic probes and controls the timing of bubble ejection in the bubble ejection mechanism based on the probability distribution of bubbles on the ultrasonic propagation path and the flow velocity distribution near the bottom. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 191096 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-163774 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the invention of Patent Document 1, it is possible to increase the frictional resistance reduction effect by air lubrication while suppressing the power required for air blowing. However, if the air blowing time can be set more appropriately, it is expected that the frictional resistance reduction effect will be further increased. The invention of Patent Document 2 uses a fluid monitoring device to control the timing of bubble ejection, which results in a complex configuration.

[0005] Therefore, an object of the present invention is to provide an air lubrication system that appropriately controls the air blowing time without complicating the configuration, suppresses the power required for air blowing, and improves the effect of reducing frictional resistance. [Means for solving the problem]

[0006] The air lubrication system with blowing time control corresponding to claim 1 is an air lubrication system that intermittently blows air onto the bottom of a ship to reduce frictional resistance of the hull, and is characterized by comprising an air outlet provided on the bottom of the ship, a ship speed detection means for detecting the ship speed, and a control means for controlling the blowing time of air intermittently blown out from the air outlet based on the set air blowing flow rate and air blowing width blown out from the air outlet and the ship speed. According to the present invention as set forth in claim 1, the air blowing time in intermittent blowing can be appropriately controlled without complicating the configuration, and the power required for air blowing can be suppressed, thereby improving the effect of reducing frictional resistance.

[0007] The present invention as set forth in claim 2 is characterized in that the control means controls the blowing time according to the ship speed within a range where the resistance reduction rate is high, based on the relationship between the equivalent air film thickness (ta) obtained by dividing the air blowing flow rate by the air blowing width and the ship speed according to Formula 1 and the resistance reduction rate of frictional resistance. Here, "Qa" is the air blowing flow rate from the air blowing port, "Bi" is the air blowing width of the air blowing port, and "V" is the ship speed.

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[0008] The present invention as set forth in claim 3 is characterized in that the control means controls the blowing time in accordance with the ship speed so that the blowing time falls within the range of the equivalent air film thickness where the drag reduction efficiency is high, based on the relationship between the drag reduction efficiency, which is obtained by dividing the drag reduction rate by the equivalent air film thickness, and the equivalent air film thickness. According to the present invention as set forth in claim 3, the blowing time is controlled to obtain an equivalent air film thickness that provides a predetermined or higher resistance reduction efficiency, thereby achieving a large frictional resistance reduction effect with a small air blowing flow rate.

[0009] In the present invention as set forth in claim 4, the control means determines the optimum equivalent air film thickness (ta) at which the equivalent air film thickness (ta) maximizes the drag reduction efficiency. Opt The blowing time is controlled according to the ship speed so that According to the present invention as set forth in claim 4, a large effect of reducing frictional resistance can be obtained with a smaller amount of air blown out.

[0010] In the present invention as set forth in claim 5, the control means controls the set optimum equivalent air film thickness (ta Opt The blowing time is controlled based on Equation 2, which expresses the relationship between the speed of the ship and the temperature of the air.

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[0011] In the present invention as set forth in claim 6, the control means controls the blowing time (T On ) is the time-averaged equivalent air film thickness in one period (ta with an overline), and the optimum equivalent air film thickness (ta Opt) and the time (T) of one cycle.

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[0012] In the present invention as set forth in claim 7, the control means controls the blowing time (T On ) is controlled to ensure 0.5 seconds or more. According to the present invention as set forth in claim 7, the effect of reducing frictional resistance can be improved more reliably than in the case of continuous blowing.

[0013] In the present invention as set forth in claim 8, the control means controls the blowing time per cycle (T) within a range of 0.75 seconds to 10 seconds. On ) and control it. According to the eighth aspect of the present invention, the effect of reducing frictional resistance can be further improved. [Effects of the Invention]

[0014] According to the air lubrication system using blowing time control of the present invention, the air blowing time in intermittent blowing can be appropriately controlled without complicating the configuration, and the power required for air blowing can be suppressed, thereby improving the frictional resistance reduction effect. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of an air lubrication system using blowing time control according to an embodiment of the present invention; [Figure 2] Graph showing the relationship between the equivalent air film thickness and the drag reduction rate obtained from the experiment [Figure 3] Graph showing the relationship between equivalent air film thickness and drag reduction efficiency per unit equivalent air film thickness [Figure 4] A graph comparing the drag reduction rate during continuous blowing and intermittent blowing. [Figure 5] Graph showing the improvement in resistance reduction rate by intermittent blowing at each ship speed [Figure 6] Graph showing the relationship between ship speed and optimal equivalent air film thickness [Figure 7] Graph showing the relationship between blowing time and drag reduction effect obtained through experiments [Figure 8] FIG. 10 is a diagram showing an example of sequence control of air blowout during intermittent blowout in an embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing another example of sequence control of air blowout during intermittent blowout. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of an air lubrication system with blowing time control according to the present invention will be described. FIG. 1 is a schematic diagram of an air lubrication system with blowing time control, where FIG. 1(a) is a side view and FIG. 1(b) is a bottom view. The air lubrication system with blowing time control (hereinafter sometimes simply referred to as "air lubrication system") equipped on the ship 1 comprises an air outlet 10 provided on the ship's bottom 1A, ship speed detection means 20 that detects the ship's speed, and control means 30 that controls the timing of air blowing from the air outlet 10, and blows air onto the ship's bottom 1A of the ship 1. The blown air turns into air bubbles that cover the ship's bottom 1A, reducing the frictional resistance of the ship while it is sailing. The boat speed detection means 20 may include, for example, a Doppler type ground / water speed meter, an electromagnetic water speed meter, a ground speed detection means using a satellite positioning system including GPS, or an estimation of boat speed from a steering handle that sets the main engine RPM or a setting signal from the main engine governor.

[0017] The air outlet 10 has an air outlet chamber 11 with a predetermined width and air outlet holes 12 provided on the side of the air outlet chamber 11 facing the bottom 1A of the ship, and is provided at one location on the bow side. In this embodiment, the width of the air outlet chamber 11 is slightly shorter than the width of the bottom 1A of the ship, and the air outlet holes 12 are provided from the left end to the right end of the air outlet chamber 11. The configuration of the air outlet hole 12 is not particularly limited, and can be, for example, a configuration consisting of an array of multiple small holes or a configuration consisting of a single long hole. The air outlet 10 can also be composed of multiple air outlets, and multiple air outlets can be arranged in the fore-and-aft direction and width direction of the bottom 1A of the ship. The air lubrication system can perform continuous air blowing from the ship's bottom 1A into the water, as well as intermittent air blowing by switching the air blowing ON / OFF every few seconds. Air can be supplied by any method, including using a blower, bypassing a turbocharger, or a combination of these. When there are multiple air outlets 10, the control means 30 can control the air blowing from each air outlet collectively or individually.

[0018] Here, Figs. 2 to 5 are graphs obtained from an experiment using the first model ship. The inventors conducted experiments on frictional resistance reduction by continuous and intermittent air blowing by towing a 50-m-long, flat-plate model ship equipped with an air blowing outlet 10 in the test tank (400 m long, 18 m wide, 8 m deep) of the National Maritime Research Institute. The long-plate model ship was designed for the purpose of measuring the frictional resistance reduction effect by conducting tests at a Reynolds number close to that of the actual ship and at the same flow velocity as the actual ship in order to reproduce both the physical phenomena related to bubbly flow and the physical phenomena related to frictional resistance under actual ship conditions. Most of the ship's bottom 1A is flat. The air blowing outlet 10 of the first model ship was installed 3 m from the bow, and the air blowing width (Bi) was set to a constant 800 mm.

[0019] Figures 2 and 3 both show data for continuous blowing, with Figure 2 showing the relationship between equivalent air film thickness (ta) and drag reduction rate (DR), and Figure 3 showing the relationship between equivalent air film thickness (ta) and drag reduction efficiency per unit equivalent air film thickness (DR / ta).In Figures 2 and 3, ● represents the case when ship speed (V) = 5.569 [m / s] (11 [kt]), ■ represents the case when ship speed (V) = 6.687 [m / s] (13 [kt]), and ▲ represents the case when ship speed (V) = 7.716 [m / s] (15 [kt]). Figure 4 is a graph comparing the resistance reduction rate during continuous blowing (blowout time uncontrolled) and intermittent blowing (blowout time controlled). Figure 4(a) is for the case where the ship speed (V) is 5.569 [m / s], Figure 4(b) is for the case where the ship speed (V) is 6.687 [m / s], and Figure 4(c) is for the case where the ship speed (V) is 7.716 [m / s]. ● is for continuous blowing, and ■ is for intermittent blowing. Figure 5 is a graph showing the improvement in resistance reduction rate (difference from the resistance reduction rate with continuous blowing) due to intermittent blowing (blow time control) for each ship speed (V). In Figure 5, ● represents the case where ship speed (V) = 5.569 [m / s], ■ represents the case where ship speed (V) = 6.687 [m / s], and ▲ represents the case where ship speed (V) = 7.716 [m / s].

[0020] As mentioned above, it is known that in a ship's air lubrication system, the equivalent air film thickness (ta) is correlated with the amount of reduction in frictional resistance. However, Figure 2 shows that the relationship between the equivalent air film thickness (ta) and the drag reduction rate (DR) is not linear (proportional). The equivalent air film thickness (ta) can be obtained by dividing the air outlet flow rate (Qa) by the air outlet width (Bi) of the air outlet 10 and the ship speed (V), as shown in Equation 1 below.

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[0021] The drag reduction efficiency (DR / ta) shown in Figure 3 is obtained by dividing the drag reduction rate (DR) by the equivalent air film thickness (ta). A large drag reduction efficiency (DR / ta) means that the drag reduction efficiency is good, that is, a large drag reduction effect can be obtained with a small air blow-out flow rate (Qa). If the relationship between the equivalent air film thickness (ta) and the drag reduction rate (DR) is proportional, the drag reduction efficiency (DR / ta) should be constant relative to the equivalent air film thickness (ta), but since the two are not proportional, it is not actually constant relative to the equivalent air film thickness (ta), and has a peak at a certain equivalent air film thickness (ta) for each ship speed (V).In Figure 3, the peak equivalent air film thickness (ta) for each ship speed is shown circled.

[0022] The equivalent air film thickness (ta) at which the drag reduction efficiency (DR / ta) is maximized is the optimal equivalent air film thickness (ta Opt Therefore, the optimum equivalent air film thickness (ta Opt By making the equivalent air film thickness (ta) as large as possible within the range not exceeding 1 / 2, the power required for air blowing can be suppressed and the drag reduction efficiency (DR / ta) can be improved. Since the air blowing width (Bi) is basically fixed, in the case of continuous blowing where air is blown out continuously in time, the equivalent air film thickness (ta) is uniquely determined for the air blowing flow rate (Qa), and the drag reduction efficiency (DR / ta) depends on the air blowing flow rate (Qa). On the other hand, the time-averaged air flow rate (Q a ) for one period (T), the optimum equivalent air film thickness (ta Opt ) etc., the time for blowing (blowing time (T On )) and the time when no blowing occurs (non-blowing time (T Off In the intermittent blowing (blowout time control) in which the air blowout flow rate (Qa) is set, the equivalent air film thickness (ta) can be changed independently of the air blowout flow rate (Qa).

[0023] Intermittent blowing time (T On ) is the instantaneous air blown out flow rate, a Then, the blowing time (T On ) and non-blowing time (T Off The relationship between the air blowout flow rate at each time is expressed as the following formula 4. a " is the time-averaged air flow rate.

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[0024] In the air blowing cycle (T), the blowing time (T On ) and non-blowing time (T Off ) the following formula 5 holds.

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[0025] Equation 6 is converted into the instantaneous air blowout flow rate (Q a ) is rearranged to obtain the following Equation 7.

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[0026] From Equation 8, it is possible to instantly form a high equivalent air film thickness (ta) by controlling the blowing time. On ) and non-blowing time (T Off ) can be used to realize any equivalent air film thickness (ta) at the time of blowing even at the same air blowing flow rate. Therefore, in the air lubrication system of the present invention, in the intermittent blowing, the control means 30 controls the blowing time (T) of the air that is blown out intermittently based on the air blowing flow rate (Qa), the air blowing width (Bi) and the ship speed (V). On ) is controlled. This controls the air blowing time (T On ) can be appropriately controlled to improve the effect of reducing frictional resistance, and the power required for blowing air can be reduced, thereby contributing to the reduction of GHG (greenhouse gases) emitted from the ship 1. Blowing time (T On) is, for example, a control of the blowing time per cycle, but other control methods are also possible, such as a control in which the time of one cycle is controlled to blow air for an actual blowing time based on a predetermined duty ratio, a control in which the time of one cycle is fixed and the duty ratio is controlled to blow air for an actual blowing time, or a control that combines these. Note that Figure 1 shows the state during intermittent blowing, with the shaded areas indicating the formed air film (air bubble film).

[0027] In addition, since the relationship between the equivalent air film thickness (ta) and the drag reduction rate (DR) is not linear, the control means 30 determines the blowing time (T On ) is controlled based on the relationship between the equivalent air film thickness (ta) and the resistance reduction rate (DR) of frictional resistance, for example, when the ship speed (V) is 5.569 [m / s], the resistance reduction rate (DR) is controlled in the range of approximately 25% to 80%, when the ship speed (V) is 6.687 [m / s], the resistance reduction rate (DR) is controlled in the range of 25% to 80% or less, and when the ship speed (V) is 7.716 [m / s], the resistance reduction rate (DR) is controlled in the range of more than 0% to 85% or less, and the resistance reduction rate (DR) is controlled in the range of more than 0% to 85% or less (see Figure 4). In this way, the blowing time (T On ) is controlled, which improves the effect of reducing the friction resistance of the hull by intermittent air blowing.

[0028] In addition, as mentioned above, the drag reduction efficiency (DR / ta) has a peak at a certain equivalent air film thickness (ta), and the instantaneous equivalent air film thickness (ta) during intermittent blowing is set to be equal to or greater than the time-averaged equivalent air film thickness and equal to or greater than the optimum equivalent air film thickness (ta Opt ) or less, the drag reduction effect can be improved. Therefore, the control means 30 adjusts the blowing time (T) in accordance with the ship speed (V) so that the resistance reduction rate (DR) is in a range where it is high and the equivalent air film thickness (ta) is in a range where it is high in the resistance reduction efficiency (DR / ta). On ) is preferably controlled. This makes it possible to obtain a large reduction in friction resistance with a small air blowout flow rate (Qa). The range in which the drag reduction efficiency (DR / ta) becomes high is the range in which the drag reduction efficiency (DR / ta) reaches its peak value in the direction in which the equivalent air film thickness (ta) increases (see Figure 3).

[0029] In the experiment, the instantaneous equivalent air film thickness (ta) was calculated as the optimal equivalent air film thickness (ta Opt The resistance reduction rate (DR) during intermittent blowing was calculated as the optimum equivalent air film thickness (ta Opt ) drag reduction efficiency (DR ta_Opt ) is expressed by the following Equation 9.

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[0030] From Figures 4 and 5, it can be seen that by controlling the blowing time so that the optimal air film thickness is achieved during air blowing, the resistance reduction rate (DR) at each ship speed (V) can be improved by up to 6 to 7% compared to the case of continuous blowing (no blowing time control). Therefore, the control means 30 determines the optimum equivalent air film thickness (ta) at which the drag reduction efficiency (DR / ta) is maximized. Opt ) according to the ship speed (V), On ) is preferably controlled. This makes it possible to improve the drag reduction effect with a smaller air blowout flow rate (Qa).

[0031] Figure 6 is a graph showing the relationship between ship speed and optimal equivalent air film thickness. Optimal equivalent air film thickness (ta Opt Since the air thickness is proportional to the ship speed (V), an approximation formula is used to calculate the optimum equivalent air film thickness (ta Opt ) can be obtained. The optimum equivalent air film thickness (ta Opt The control means 30 determines the set optimum equivalent air film thickness (ta Opt ) and ship speed (V) based on Equation 2,On ) can improve the effect of reducing frictional resistance.

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[0032] FIG. 7 is a graph showing the relationship between blowing time and drag reduction effect obtained from an experiment using the second model ship. In the same test tank as the experiment using the first model ship, an experiment on frictional resistance reduction by air lubrication was conducted by towing a long, flat model ship with a total length of 36 m and equipped with an air outlet 10. The air outlet 10 of the second model ship was installed 3 m from the bow, and the air outlet width (Bi) was set to a constant 800 mm. In this experiment, the time-averaged equivalent air film thickness (ta) was 4.5 mm, and the blowing time (T On ) is set to five values: 0.5 [s], 1.0 [s], 1.5 [s], 2.0 [s], and 2.5 [s]. On ) and non-blowing time (T Off ) were of equal length and repeated periodically. From Equation 8, equivalent air film thickness (ta) = 2 × time-average equivalent air film thickness (ta with overline), and it can be seen that when air is blown out, the equivalent air film thickness (ta) is twice the time-average. In this case, from Equation 9, the expected drag reduction effect is half of the drag reduction amount when the time-averaged equivalent air film thickness (overlined ta) in continuous blowing is 9.0 [mm].

[0033] From Figure 7, the blowing time (T On ) the resistance reduction effect is greater than in the case of continuous blowing. On ) is preferably controlled to ensure 0.5 seconds or more. Also, from Figure 7, the blowing time (T On ) increases, the drag reduction effect increases, and T On = 2.0 [s], the expected drag reduction effect is close, and T On= 2.5 [s], it can be seen that this coincides with the expected drag reduction effect. This is thought to be because the drag reduction effect has a phase lag relative to the air blowing. Therefore, the blowing time (T On ) is more preferably 2.0 [s] or more, and most preferably 2.5 [s] or more.

[0034] FIG. 8 shows an example of sequence control of air blowing during intermittent blowing. The solid line in the figure shows the change in equivalent air film thickness at a certain point during intermittent blowing, and the dotted line shows the equivalent air film thickness during continuous blowing at the same time average flow rate. The conditions for the control method in this example are shown in Table 1 below. In Table 1 below, the instantaneous equivalent air film thickness (ta) is calculated as the optimum equivalent air film thickness (ta) for each ship speed (V) [m / s]. Opt The control conditions for intermittent blowing are summarized below. When blowing intermittently, a thicker equivalent air film thickness (ta) is formed instantaneously compared to when blowing continuously, achieving a high drag reduction effect. From Equation 8, the air blowing period (T) and the air blowing time (T On Any equivalent air film thickness (ta) can be realized by the ratio of the time-averaged equivalent air film thickness (ta) to the optimum equivalent air film thickness (ta Opt ) is less than the air flow rate, the control of the formula 8 is performed. On ) is most preferably 2.5 [s] or more. [Table 1]

[0035] Air blowing time (T On ) and non-blowing time (T Off ) can be calculated from the following formulas 10 and 11 using formulas 5 and 8.

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[0036] From Equation 10, in order to increase the equivalent air film thickness (ta) when the air blowing period (T) is constant, the air blowing time (T On ) needs to be reduced. Furthermore, from Equation 11, the air blowing time (T On In order to increase the equivalent air film thickness (ta) when air is blown out at a constant value, the air non-blowing time (T Off ) needs to be increased. In this case, according to Equation 5, the air blowing period (T) also increases.

[0037] The control means 30 controls the blowing time per cycle of air (T On ) is the time-averaged equivalent air film thickness in one period (ta) and the optimum equivalent air film thickness (ta Opt ) and the time of one cycle (T) is controlled based on the following formula 3. On ) can be accurately calculated and controlled using Equation 3.

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[0038] As mentioned above, the blowing time per cycle (T On It is preferable to secure 0.5 seconds or more for the blowing time per cycle (T), but taking the duty ratio into consideration, the control means 30 sets the blowing time per cycle (T) within the range of 0.75 seconds or more and 10 seconds or less. On ) is preferably calculated and controlled. This makes it possible to further improve the effect of reducing frictional resistance. The control means 30 controls the blowing time per cycle (T On In addition to controlling the airflow, it is also possible to select continuous airflow, start and stop the air supply, and start, stop, or switch the air supply source in conjunction with other controls.

[0039] FIG. 9 shows another example of sequence control of air blowing during intermittent blowing. In the figure, the solid line shows the change in equivalent air film thickness (ta) at a certain point during intermittent blowing, and the dotted line shows the equivalent air film thickness (ta) during continuous blowing at the same time average flow rate. Air blowing time (T On ) and non-blowing time (T Off ) are equal, that is, when it becomes a square wave as shown in Figure 9, the air blowing time (T On The relationship between the temperature (T) and the air blowing cycle time (T) is expressed by the following formula 12, and the conditions for the control method are shown in Table 2 below.

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[0040] The present invention can improve the propulsion efficiency of a ship, reduce the power required for blowing air, and contribute to reducing GHG emissions from the ship. The present invention can be applied not only to ships newly equipped with an air lubrication system, but also to ships already equipped with an air lubrication system. [Explanation of symbols]

[0041] 1 ship 1A Ship bottom 10 Air outlet 20 Ship speed detection means 30 Control Means

Claims

1. An air lubrication system that intermittently blows air onto the bottom of a ship to reduce frictional resistance of the hull, comprising an air outlet provided on the bottom of the ship, a ship speed detection means for detecting the ship speed, and a control means for controlling the blowing time of the air that is intermittently blown out from the air outlet based on the set air blowing flow rate and air blowing width blown out from the air outlet and the ship speed.

2. 2. The air lubrication system with blowing time control according to claim 1, characterized in that the control means controls the blowing time according to the ship speed within a range in which the resistance reduction rate is high, based on the relationship between the equivalent air film thickness (ta) obtained by dividing the air blowing flow rate by the air blowing width and the ship speed based on Equation 1 and the resistance reduction rate of the frictional resistance. [Equation 1] ta: Equivalent air film thickness Qa: Air blowout volume Bi: Air blow width V: Ship speed

3. 3. The air lubrication system with blowing time control according to claim 2, wherein the control means controls the blowing time in accordance with the ship speed based on the relationship between the drag reduction efficiency, obtained by dividing the drag reduction rate by the equivalent air film thickness (ta), and the equivalent air film thickness, so that the drag reduction efficiency is in a range of equivalent air film thickness where the drag reduction efficiency is high.

4. The control means controls the equivalent air film thickness (ta) so that the equivalent air film thickness (ta) is the optimum equivalent air film thickness (ta) at which the drag reduction efficiency is maximized. Opt 4. The air lubrication system with blowing time control according to claim 3, wherein the blowing time is controlled in accordance with the ship speed so that the blowing time is equal to or greater than the ship speed.

5. The control means controls the set optimum equivalent air film thickness (ta Opt 5. An air lubrication system with blowing time control according to claim 4, characterized in that the blowing time is controlled based on Equation 2 which expresses the relationship between the speed of the vessel and the amount of water vapor. [Equation 2] ta Opt : Optimum equivalent air film thickness V: Ship speed

6. The control means controls the blowing time (T On ) is the time-averaged equivalent air film thickness in one period (ta with an overline), and the optimum equivalent air film thickness (ta Opt 6. The air lubrication system with blowing time control according to claim 5, wherein the blowing time is controlled based on Equation 3, which expresses the relationship between the blowing time (T) and the time period (T) of one cycle. [Equation 3] Overlined ta: Time-averaged equivalent air film thickness per cycle ta Opt : Optimum equivalent air film thickness T: Time for one cycle T On : Blowing time per cycle

7. The control means controls the blowing time (T On 7. The air lubrication system with blowing time control according to claim 6, wherein the blowing time is controlled so as to ensure 0.5 seconds or more.

8. The control means controls the blowing time per cycle (T) within a range of 0.75 seconds to 10 seconds. On 7. The air lubrication system with blowing time control according to claim 6, wherein the blowing time is controlled by calculating and controlling the blowing time.

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