JP3321772B2 - Ship's cathodic protection system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion apparatus for preventing an anticorrosion target (electrochemical corrosion) of a hull, a propeller, a propeller shaft and the like of a ship.

[0002]

2. Description of the Related Art A sacrificial anode (also referred to as a galvanic anode) is one of the means for preventing catastrophic damage to ships.

[0003] This is because a sacrificial anode made of a metal such as zinc, aluminum, or magnesium is attached to a corrosion-protected body consisting of a hull, a propeller, a propeller shaft, a rudder, and the like, thereby forcing a predetermined negative potential. Is to be granted.

[0004] In this case, there is an ideal range for the potential of the body to be protected in seawater, and the potential is the corrosion protection potential of the body to be protected (this is the potential where corrosion protection works, for example, in the case of iron). (-780 mV, -830 mV for aluminum)
When it is higher (ie, on the plus side), electrolytic corrosion occurs. On the other hand, when it is much lower (ie, on the minus side), there is a problem that overcoating is caused and the coating film on the hull is peeled off by alkali. It should be noted that the values of the potential of the object to be protected in seawater in this specification are all based on the silver chloride electrode.

[0005] However, the potential of the body to be protected in seawater greatly changes due to changes in the corrosive environment such as the speed of the ship, and the energy of the sacrificial anode is determined by its material and size. Since the current cannot be changed flexibly in response to changes in the corrosive environment, even if the potential of the eroded body at rest is ideal, the potential will be higher during navigation. If the sacrificial anode is increased so that the potential during navigation is ideal, the weight increases and the potential of the protected body becomes too low while the ship is stopped. There is a problem that over-corrosion occurs.

To solve such a problem of the sacrificial anode method, there is an external power supply method employing automatic control.

A conventional example of this type of cathodic protection apparatus is shown in FIG.
This will be described with reference to FIG. The cathodic protection device 26 includes a variable output DC power supply 28, a control circuit 30 for controlling the DC power supply 28, and a seawater 10 outside the hull 14 of the ship 12.
An anode 32 and a reference electrode 34, which are attached to the part immersed therein while being electrically insulated from the hull 14, are provided.
A positive potential is applied from the DC power supply 28 to the anode 32 relative to the hull 14, the propeller shaft 16, the propeller 18, the overhang bearing 20.
The anticorrosion current I is supplied to these anticorrosion objects through the seawater 10 from the anode 32 by collectively applying a negative potential to the anticorrosion objects including the rudder 24 and the like. The propeller shaft 16 is slidably contacted with a brush 36 that performs both potential application and potential detection.

In addition, the potential of the corrosion-protected body (more specifically, of the hull 14 occupying most of the body) in the seawater 10 is detected by using the reference electrode (silver chloride electrode) 34, and the potential is detected. In order to approach the set potential E (for example, -900 mV),
The anticorrosion current I output from the DC power supply 28 is automatically controlled by the control circuit 30.

According to the above-described cathodic protection device 26, even if the corrosive environment changes, the potential of the anticorrosion target can be kept close to a constant value. Can be prevented.

[0010]

However, even with the provision of the above-described cathodic protection device 26 of the external power supply type, the phenomenon that corrosion occurs in the propeller 18, especially in the vicinity of the blade root thereof, has conventionally occurred. .

Conventionally, such corrosion is attributable to erosion corrosion mainly caused by cavitation, which is different from electrochemical corrosion, and it has been considered that such corrosion cannot be suppressed by an electrolytic protection apparatus.

In order to prevent such corrosion, conventionally, for example, a hole 182 called a cavitation hole is provided in the blade root portion of the propeller 18, and through this, the propeller 1
In some cases, the seawater 10 may be supplied from the pressure surface side of the blades 181 to the rear surface where the water separation phenomenon is likely to occur. However, this is not so effective, and the cavitation hole 182 is not provided to the propeller 18. In order to reduce the strength of the cavitation hole 182, the blade root of the propeller 18 needs to be thickened and the propeller efficiency deteriorates.
And other problems have arisen.

Moreover, the corrosion of the propeller 18 becomes more severe as the speed of the ship 12 increases. For example, even though the ship has a maximum sailing speed of 37 knots, the propeller 18 undergoes severe corrosion during high speed sailing. Is 25
In some cases, it is limited to less than a knot.

Therefore, the present invention improves the above-described cathodic protection system, thereby effectively preventing not only the electrochemical corrosion of the hull but also the above-mentioned corrosion of a propeller which has been considered impossible before. The main purpose is to be able to control.

[0015]

In order to achieve the above object, a first cathodic protection device according to the present invention is mounted on a portion outside the hull of a ship and submerged in seawater while being electrically insulated from the hull. The first anode and the first anode are provided with a relatively positive potential, and the boat is provided with a negative potential relatively with respect to a propeller shaft and a shaft system including a propeller attached thereto. A variable direct-current power supply for supplying an anticorrosion current to the shaft system from the anode of the ship through the seawater, and a collation mounted electrically insulated from the hull outside the hull of the ship and submerged in the seawater An electrode, a first control circuit for controlling an anticorrosion current output from the first DC power supply so that the potential of the shaft system with respect to the reference electrode approaches a preset potential, and a seawater outside the hull of the ship. Electrically disconnected from the hull in the part that sinks inside A second positive electrode attached to the hull of the ship, and a negative potential is applied to the hull of the marine vessel. By measuring the potential difference between the output-variable second DC power supply that supplies the current and the shaft system and the hull,
A second control circuit for controlling an anticorrosion current output from the second DC power supply device so that the potential of the hull is on the plus side by a preset potential difference from the potential of the shaft system.

[0016] The second cathodic protection device of the present invention comprises:
A first anode electrically insulated from the hull outside the hull of the ship and submerged in seawater;
A positive potential is applied relatively to the anode of the vessel, and a negative potential is applied relatively to the shaft system including the propeller shaft of the ship and the propeller attached thereto, so that anticorrosion current is applied to the shaft system through seawater from the first anode. A variable output first direct-current power supply, a first reference electrode that is attached to a portion outside the hull of the ship and submerged in seawater and is electrically insulated from the hull;
A first control circuit for controlling an anticorrosion current output from the first DC power supply so that the potential of the shaft system with respect to the first reference electrode approaches a preset potential; A second anode which is electrically insulated from the hull at a portion to be immersed therein, and which applies a relatively positive potential to the second anode and a relatively negative potential to the hull of the ship. A variable output second DC power supply for supplying an anticorrosion current to the hull through seawater from the second anode, and a portion of the hull outside the hull and submerged in the seawater, which is electrically insulated from the hull and mounted. The second reference electrode and the second reference electrode so that the potential of the hull with respect to the second reference electrode is on the plus side by a preset potential difference from the set value of the potential in the first control circuit. Control the anticorrosion current output from the DC power supply And a second control circuit.

[0017]

[Action] As a result of repeated experiments, the anticorrosion device is configured as described above, and the anticorrosion current is supplied to the shaft system and the hull using another DC power supply device, and the electric potential of the shaft system is mainly used. ,
By controlling the potential of the hull to be on the plus side by a preset potential difference from the potential of the shaft system, not only electrolytic corrosion of the hull but also corrosion of the propeller could be effectively suppressed. The reason is as follows.

That is, in a ship, the relative velocity of water flow with respect to the propeller is much higher than that of other parts, and the oxide film on the surface of the propeller is peeled off by water hammer due to cavitation or dust in the water to become bare metal. For,
The propeller is in a situation where the ionization tendency is more likely to be activated (that is, more easily mobilized) than other parts. Therefore, even if the conventional external power supply type anticorrosion device is provided as described above, the potential of the propeller is highest (for example, -750 mV to -750) with respect to the potential of the hull (for example, about -900 mV).
(Approximately 350 mV), and a phenomenon occurs in which current flows from the propeller through seawater to a lower potential, for example, to an overhang bearing or a hull that rotatably supports the propeller shaft. This is as if the propeller acts as a sacrificial anode, as described above, thereby subjecting the propeller to electrochemical corrosion. In addition, as the speed of the ship increases, the propeller becomes more active and the electrochemical corrosion of the propeller increases.

Conventionally, propeller corrosion was considered to be mostly caused by erosion due to cavitation water hammer. However, as a result of various experiments, the inventor has found that propeller corrosion is the above-mentioned electrochemical corrosion. It was found that this was a merger with erosion due to water hammer, and that it was greater due to electrochemical corrosion.

In order to suppress the electrochemical corrosion of a propeller,
It was found that a sufficient anticorrosion current should be supplied from the anode to the propeller which easily moves through seawater, and the potential of the shaft system including the propeller in the seawater should be sufficiently reduced. This potential is preferably in the range of, for example, -980 mV to -1050 mV.

In that case, like a conventional cathodic protection device,
In the system that controls the electric potential of the entire body to be protected including the hull and the shaft system at the same time, the hull whose area in seawater is extremely large compared to the shaft system is the subject of control. The potential alone cannot be reduced sufficiently as described above. If the potential of the entire body to be protected including the hull and the shaft system is sufficiently reduced as described above, it is necessary to flow a very large corrosion protection current, so the output power of the cathodic protection device must be very large. As it disappears, the potential of the hull drops too much and it becomes anticorrosion, the coating of the hull peels off,
There are problems such as hydrogen embrittlement of the metal constituting the hull.

On the other hand, in the present invention, the DC power supply and the control circuit are provided for the shaft system and the hull, respectively, so that a sufficient anticorrosion current is supplied to the shaft system so that only the potential of the shaft system is controlled. Can be lowered enough. As a result, electrochemical corrosion of the propeller can be effectively suppressed while preventing excessive corrosion of the hull.

Further, when the potential difference between the shaft system and the hull becomes too large, one having a relatively high potential (specifically, the hull) is switched from the other having a relatively low potential (specifically, the shaft system).
The current flowing in a liquid junction through seawater cannot be ignored, and this may cause local corrosion at a portion where the current of the hull flows out. In the present invention, however, the potential of the hull is reduced by the second control circuit. Since it is controlled to be on the plus side by a preset potential difference from the potential of the shaft system,
The occurrence of such local corrosion can be suppressed. This potential difference is preferably in the range of, for example, 80 mV to 120 mV.

[0024]

FIG. 1 is a schematic diagram showing an electric anticorrosion device for a ship according to an embodiment of the present invention.

In this example, the marine vessel 42 rotatably supports a hull 44, a propeller 48, a propeller shaft 46 coupled to the propeller 48 for rotating the propeller 48, and a propeller shaft 46 near the propeller 48. Overhang bearing 50,
A bracket 5 for supporting the overhang bearing 50 from the hull 44
2 and a rudder 54. The propeller shaft 46 and the propeller 48 are connected to each other not only mechanically but also electrically, for example, by fitting. 10 is seawater.

The material of the hull 44 is, for example, iron, aluminum, high-tensile steel or the like. The material of the propeller 48 is, for example, a bronze alloy, aluminum bronze, or the like. The material of the propeller shaft 46 is, for example, stainless steel.

The cathodic protection device 56 of this embodiment is of an external power supply type, and is attached to a portion of the ship 42 outside the hull 44 and submerged in the seawater 10 so as to be electrically insulated from the hull 44. A positive potential is applied to the anode 66 and the anode 66 relatively, and a negative potential is applied to the shaft system 45 including the propeller shaft 46 of the ship 42 and the propeller 48 attached thereto, so that the seawater A variable output first DC power supply 58 for supplying an anticorrosive current to the shaft system 45 through the power supply 10, and a portion of the watercraft 42 outside the hull 44 and submerged in the seawater 10 and electrically insulated from the hull 44. Reference electrode 68 and the axis system 4 for the reference electrode 68.
A first control circuit 60 for controlling the anticorrosion current I ₁ output from the DC power supply 58 so that the potential of the DC-DC converter 5 approaches the preset potential E ₁ ; By giving a negative potential relatively to the hull 44 of 42,
A variable output second DC power supply 62 for supplying an anticorrosion current to the hull 44 from the anode 66 through the seawater 10 and a shaft system 45;
The potential difference between the hull 44 and the hull 44 is measured, and the anticorrosion current I ₂ output from the DC power supply 62 so that the potential of the hull 44 is on the plus side by a preset potential difference E ₂ from the potential of the shaft system 45. And a second control circuit 64 for controlling

The anode connected to the DC power supply 58 (first anode) and the anode connected to the DC power supply 62 (second anode) may be provided separately. As described above, one anode 66 may also be used, and in such a case, it becomes economical.

The anode 66 is preferably provided near the propeller 48 as in this embodiment. By doing so, the propeller 48, which can be easily activated, is placed near the seawater 1
This is because a sufficient anticorrosion current can be supplied through 0, which is advantageous in suppressing electrochemical corrosion of the propeller 48.

The anode 66 is formed, for example, by plating platinum on the surface of titanium. The reference electrode 68 is also called a reference electrode, and is an electrode having a constant potential in the seawater 10, for example, a silver chloride electrode.

The propeller shaft 46 has a brush 70 for applying a negative potential relative to the shaft system 45 from the DC power supply 58 in the hull 44 and a detection brush for detecting the potential of the shaft system 45. Brush 72 is in sliding contact. The material of the applying brush 70 is, for example, copper 50
%, 50% carbon. Detection brush 72
Is a mixture of, for example, 50% silver and 50% carbon.

It is preferable that the brush for applying the potential and the brush for detecting the potential are not shared with each other but are separately provided as in this embodiment. The reason is that there is a large distance between the potential applying brush and the propeller shaft 46 (for example, several A to several tens A).
), The corrosion protection current flows, so the voltage drop there is large,
This is because if both are used, this voltage drop affects the potential detection of the shaft system 45 and causes a detection error. Apart from this embodiment, the detection brush 72 and the propeller shaft 46 are separated.
Since almost no current flows between the two, the detection error due to the contact resistance there can be ignored.

The control circuit 60 determines the difference between the potential of the axis system 45 in the seawater 10 and the potential of the reference electrode 68 as shown in FIG.
A subtraction circuit 78 for detecting the potential E _S of the
8 and obtains the difference between the potentials E ₁ which is set in advance to a potential E _S detected (i.e. E _S -E _1), the signal S proportional to the difference
A subtraction circuit 80 for outputting ₁ and a diode 81 for outputting this signal S ₁ only when it is positive are provided.

In response to the signal S ₁ supplied from the control circuit 60, the DC power supply 58 outputs an anticorrosion current I ₁ proportional to the value. Subtraction of protection current I ₁ is carried out for example by elevating the output voltage (e.g., 0 - 12v). For example, when the potential E _S is higher than the potential E ₁ and the difference between them is large, the signal S ₁ output from the subtraction circuit 80 has a large positive value, and the anticorrosion current I ₁ output from the DC power supply device 58 Therefore, the anticorrosion current flowing from the anode 66 to the shaft system 45 through the seawater 10 to the shaft system 45 increases, thereby lowering the potential of the shaft system 45, and as a result, the difference becomes smaller. When the potential of the shafting 45 falls below the set potential E _1,
The signal S ₁ output from the subtraction circuit 80 becomes negative, which is blocked by the diode 81 and is not output. As a result, the anti-corrosion current I ₁ is zero output from the DC power supply device 58, the potential of in seawater 10 resulting shafting 45 rises. The DC power supply 58 is, to put it another way, a control circuit 60.
It is as power amplifier circuit of the signals S ₁ supplied from.

[0035] With this configuration, the potential of the shafting 45 in seawater 10 is automatically controlled to the set potential E _1.

The potential control circuit 64, for example as shown in FIG. 3, a subtraction circuit 82 for detecting a potential difference E _D between the hull 44 and the shaft system 45 in seawater 10, detected by the subtraction circuit 82 and obtains the difference between the potential difference E ₂ set in advance and E _D (i.e. E _D -E _2), if a subtraction circuit 84 for outputting a signal S ₂ which is proportional to the difference, the signal S ₂ is that of the positive And a diode 85 for outputting only to the

In response to signal S ₂ supplied from control circuit 64, DC power supply 62 outputs anticorrosion current I ₂ proportional to the value. Subtraction of protection current I ₂ is carried out for example by elevating the output voltage (e.g., 0 - 12v). For example, when large and the difference between them than it is to a potential difference E ₂ potential difference E _D is large, the signal S ₂ output from the subtracting circuit 84 protection current output from the DC power supply device 62 becomes a positive large value I ₂ also increases, the anticorrosion current flowing from the anode 66 to the hull 44 through the seawater 10 increases,
As a result, the potential of the hull 44 decreases, and as a result, the difference decreases. When a potential difference E _D is smaller than the set potential E ₂ (i.e. when the potential of the hull 44 is too low), the signal S ₂ output from the subtracting circuit 84 becomes negative, it is not output is blocked by the diode 85. As a result, the anticorrosion current I ₂ output from the DC power supply 62 is reduced to zero,
As a result, the potential of the hull 44 in the seawater 10 increases. The DC power supply 62 is like a power amplifier for the signal S ₂ supplied from the control circuit 64.

With this configuration, the potential of the hull 44 in the seawater 10 is set to a potential difference E higher than the potential of the shaft system 45.
It is automatically controlled to be on the plus side for ₂ minutes.

The set potential E in the control circuit 60 described above.
Preferably, ₁ is set, for example, in the range of -980 mV to -1050 mV. This is because the electric potential is too high on the plus side than -980 mV, and the anticorrosion effect of the propeller 48 is inferior. Conversely, the anticorrosion effect of the propeller 48 hardly increases even when it is on the minus side below -1050 mV. This is because only the output power has to be increased.

It is preferable that the set potential difference E ₂ in the control circuit 64 is set in a range of, for example, 80 mV to 120 mV. If the electric potential of the hull 44 is less than 80 mV, the potential of the hull 44 may approach the potential of the shaft system 45 too much, and the hull 44 may be excessively protected. Is worsened, and the current flowing from the hull 44 through the seawater 10 to the shaft system 45 in a liquid junction cannot be ignored. For example, as shown in FIG.
Numeral 6 penetrates the hull 44 through a stern tube 92 provided at the bottom of the hull, and the seawater 10 has entered the gap 93 between the stern tube 92 and the propeller shaft 46, and this gap 9
3 from the hull 44 through the seawater 10 to the propeller shaft 4
A current flows in a liquid junction to 6. When such a current flows, the stern tube 92 becomes sacrificial anodized and easily corrodes, and since this current is eventually supplied from the DC power supply 58, its output power must be increased. Setting the potential difference E ₂ by within the above range, it is possible to prevent such problems from occurring. In addition, 94 in FIG. 4 is a water sealing part.

[0041] Particularly, when the material of the hull 44 is aluminum, the set potential E ₁ to about -1000 mV, it is highly preferred to approximately 100mV the setting potential E ₂ was confirmed by experiment.

Overhang bearing 50, bracket 52 and rudder 5
4 are electrically connected in parallel to the hull 44 in this example, so that they are collectively subjected to anticorrosion with the hull 44. However, a DC power supply device for the rudder 54 and a control circuit therefor are separately provided, and the potential of the rudder 54 in the seawater 10 is controlled by the hull 44.
May be controlled separately from the above potential.

As a bearing material (a bush) provided in the overhang bearing 50 and rotatably supporting the propeller shaft 46, a material made of rubber or fluororesin is generally used instead of a metal material. Therefore, the propeller shaft 46 is electrically insulated from the overhang bearing 50 by the supporting member.

On the other hand, the propeller shaft 46 is connected to the output shaft of the main engine in the hull 44, and when the potential difference E ₂ is provided between the hull 44 and the shaft system 45 as described above, It cannot be said that there is no risk of leakage current flowing between the hull 44 and the shaft system 45 via the engine. Therefore, as shown in FIG. 4, an insulator 1 is attached to a portion of the coupling 100 that couples the propeller shaft 46 and the output shaft 98 of the main engine 96.
It is preferable that the propeller shaft 46 and the output shaft 98 be completely electrically insulated by the insulator 102.
Thus, when via the main engine 96 leakage since current may completely eliminated flowing between the hull 44 and the shaft system 45, giving a potential difference E ₂ between the hull 44 and the shaft system 45, It is not necessary to apply extra energy to the shaft system 45, and the output power of the DC power supply device 58 can be saved. It is preferable to use a material having high mechanical strength and high electrical insulation, such as a glass epoxy resin, for the insulator 102.

As shown in FIG. 5, the application brushes 70 are arranged so as to be opposed to each other with the propeller shaft 46 interposed therebetween, and are electrically connected in parallel to each other. ) It is preferable to constitute the brushes 701 and 702. By doing so, even if the propeller shaft 46 has a runout or the like, at least one of the brushes 701 or 7
02 because surely contact with the propeller shaft 46, by applying a negative potential stably the shaft system 45 from a DC power supply unit 58, a protection current I ₁ can flow stably. Similarly, as shown in FIG. 5, the above-described detection brushes 72 are arranged so as to face each other with the propeller shaft 46 interposed therebetween, and are electrically connected in parallel to each other. ) It is preferable to constitute the brushes 721 and 722. In this case, even if the propeller shaft 46 has a runout or the like, at least one of the brushes 721 or 722 surely contacts the propeller shaft 46, so that the potential of the shaft system 45 can be detected stably. .

According to the above-described cathodic protection device 56,
Since the anticorrosion current I ₁ is sufficiently supplied to the shaft system 45 to sufficiently lower the potential of the shaft system 45, electrochemical corrosion of the propeller 48 can be effectively suppressed. Moreover,
Since the potential of the hull 44 can be kept only in the positive side _half potential difference preset than the potential of the shafting 45 E, it is possible to prevent excessive corrosion of the hull 44, the hull 44
Current can be prevented from flowing through the seawater 10 to the shaft system 45 through a liquid junction.

As a result, the corrosion of the propeller 48, which has been considered impossible in the past, particularly in the vicinity of the blade root, can be effectively suppressed by the cathodic protection device 56. As a result, the life of the propeller 48 can be greatly extended without providing a cavitation hole unlike the related art.
In addition, when the cavitation hole is not provided, the processing of the propeller 48 becomes easy, and the thickness of the root portion of the blade 481 of the propeller 48 can be reduced, so that the propeller efficiency does not decrease.

By the way, in addition to the above-described external power supply type anti-corrosion device 56, for example, as shown in the embodiment shown in FIG.
It is preferable to attach a sacrificial anode (first sacrificial anode) 76 to the rear end of 6. A detailed example of how to attach the sacrificial anode 76 to the propeller shaft 46 will be described later with reference to FIG.

The sacrificial anode 76 is, for example, an alloy containing aluminum, zinc or magnesium as a main component. The material and size of the sacrificial anode 76 depend on environmental conditions, anticorrosion specifications, and the set potential E ₁ in the control circuit 60. What is necessary is just to select suitably according to a value etc.

As described above, the sacrificial anode 76 is connected to the propeller shaft 4
By attaching to the rear end of this sacrificial anode 7
6 can supply a stable anticorrosion current to the propeller 48 through the seawater 10, so that the shaft system 45 can be supplied through the seawater 10 from the above-described external power supply type anticorrosion device 56, more specifically, from the DC power supply device 58. Even if disturbance such as pulsation occurs in the anticorrosion current supplied to the motor, the disturbance is smoothed by the anticorrosion current from the sacrificial anode 76 and the propeller 48
The anticorrosion current can be supplied stably. As a result, electrochemical corrosion of the propeller 48 can be suppressed more reliably.

By the way, the DC power supply 58 is connected to the shaft system 45.
The above-described disturbance of the anticorrosion current supplied to the brush may be caused by chattering in the application brush 70, for example. Chattering in this application brush can be considerably reduced by using a pair of brushes 701 and 702 as described above with reference to FIG. 5, but even in this case, if the sacrificial anode 76 is provided, The influence of the chattering can be extremely reduced.

Further, a second sacrificial anode 116 is further mounted at a position outside the hull 44 of the ship 42 and immersed in the seawater 10 when the ship 42 is stopped and rises above the sea surface during navigation, and the first sacrificial anode 116 is provided. It is preferable to provide a hollow portion whose rear portion communicates with the outside in the sacrificial anode 76 of FIG.

As a preferable example of the above-described position where the sacrificial anode 116 is provided, as shown in FIG. 6, the outer side of the stern outer plate 441 of the ship 42 and below the water level line 10a of the seawater 10 at the time of stoppage. And there are several (not limited to five as in the illustrated example) sacrificial anodes 11
6 is attached.

The sacrificial anode 116 is also an alloy containing, for example, aluminum, zinc or magnesium as its main component, but its material, size, number, etc. may be appropriately selected according to environmental conditions, anticorrosion specifications and the like.

A detailed example of how to attach the sacrificial anode 76 to the propeller shaft 46 will be described with reference to FIG. The propeller 48 has a boss 482, and the boss 482 has a tapered through hole 483 that spreads forward. The propeller shaft 46 has a boss 48 near its rear end.
2 has a tapered shape corresponding to the second through hole 483 and has a male screw portion 462 at the rear end.
6 is fitted into the through hole 483 of the boss 482 and the propeller 48 is fitted to the propeller shaft 4 by fitting.
6 Further, the male screw 462 is connected to the boss 482
From the rear end face of the male screw 4
A propeller nut 74 is screwed into 62 to prevent the propeller 48 from coming off. And this propeller nut 7
The sacrificial anode 76 is disposed at the rear end of the fourth. The sacrificial anode 76 has a cylindrical shape with a bottom in this example, and has a hollow portion 762 in which a rear portion communicates with the outside and a front portion 761 is closed.

In this example, a bolt 86 having a tapered tip 861 having a distal end portion 861 and an intermediate portion 862 extending toward a head portion 863 is used, and a male screw portion 462 at the rear end of the propeller shaft 46 is provided. A female screw portion 463 to be screwed to the bolt 86 is provided, and a through hole 763 which is tapered corresponding to the intermediate portion 862 of the bolt 86 is provided in the front surface portion 761 of the sacrificial anode 76. The sacrificial anode 76 is fixed to the rear end of the propeller shaft 46 with the bolt 86 through the bolt 86. Further, in this example, between the sacrificial anode 76 and the rear end face 464 of the propeller shaft 46,
A ring-shaped first packing 88 surrounding the bolt 86 is provided, and a second ring-shaped packing 90 surrounding the bolt 86 is provided between the sacrificial anode 76 and the vicinity of the head of the bolt 86.

The bolt 86 is made of, for example, an alloy of titanium 64, 6 aluminum and 4 vanadium. The packings 88 and 90 are O-rings made of, for example, rubber, fluorine resin, or the like.

By providing the first sacrificial anode 76 and the second sacrificial anode 116 as described above, it is not necessary to operate the external power supply type anticorrosion device 56 while the ship 42 is stopped, so that the maintenance and the like are very difficult. The effect that it becomes easy is obtained.

More specifically, since the externally-powered cathodic protection system generally has to operate continuously even when the ship is berthed for a long period of time, there is a problem in that maintenance and management thereof are troublesome. .

For example, even in the case of an anticorrosion device for a small boat having a total length of about 20 m, for example, even at a berth, for example, a DC 24 V
Therefore, an input of at least about 3 to 4 A is required (by the way, a large anticorrosion current is required during navigation, so an input exceeding 10 A is required). During berthing, the engine of the ship and the generator connected to it are not running, so this power is usually supplied from the battery.However, since the large input is required as described above, the engine is sometimes turned on. This battery has to be charged, which is very troublesome. This is not possible if the crew is out of the office for a long time.

There is also a method of supplying commercial power from land, but the wiring and the like are troublesome, and depending on the berth, it may not be possible in some cases.

If the cathodic protection device does not work due to exhaustion of the battery or the like, there is a danger that the hull and the shaft system of the ship will be corroded.

On the other hand, the sacrificial anode 76 as described above is used.
Is provided, the sacrificial anode 76 is always submerged in the seawater 10, and when the ship 42 is stopped,
Since the seawater 10 also enters the inside 62 and the sacrificial anode 76 is in contact with the seawater 10 in a large area, the sacrificial anode 76
, A sufficient anticorrosion current can be supplied to the shaft system 45 including the propeller 48 through the seawater 10 to prevent such electrolytic corrosion. Further, if the sacrificial anode 116 is provided, the sacrificial anode 116 is immersed in the seawater 10 while the ship 42 is stopped.
Thus, a sufficient anticorrosion current can be supplied to the hull 44 and also to the overhang bearing 50 and the rudder 54 connected in parallel to the hull 44 so as to prevent the electrolytic corrosion thereof. In addition, when the ship is stopped, the corrosive environment hardly changes unlike during navigation, so that even when the sacrificial anodes 76 and 116 are used, electrolytic corrosion of the shaft system 45 and the hull 44 can be effectively prevented.

Therefore, when the ship 42 is stopped, it is not necessary to operate the external power-supply type anticorrosion device 56, so that maintenance and the like thereof are greatly facilitated. For example, when the ship 42 is in a long term berth, if the switch of the cathodic protection device 56 is turned off, it is not necessary to supply power from a battery or the like. Therefore, it is possible to cope with a case where the seafarer is absent for a long period of time or a case where commercial power cannot be supplied from land. Since the power consumption of the control circuits 60 and 64 is extremely low, the hull 44
Alternatively, only monitoring of the potential of the bearing 45 may be continued.

On the other hand, when the ship 42 is in the course of navigation, the cathodic protection device 56 is operated, and the shaft system 45 including the propeller 48 and the hull Electrolytic corrosion such as 44 can be effectively prevented. Therefore, in this case, there is no need to operate the sacrificial anode 116. Also, the sacrificial anode 76 may be operated to such an extent that the disturbance of the anticorrosion current supplied from the DC power supply device 58 to the shaft system 45 through the seawater 10 can be smoothed.

Therefore, in this embodiment, as described above, the hollow portion 7 whose rear portion communicates with the inside of the sacrificial anode 76 is formed.
62 is provided, so that the seawater 10 is sucked into the hollow portion 762 during the navigation of the ship 42 to be in a vacuum state, so that the seawater 10 mainly contacts only the outer peripheral portion of the sacrificial anode 76. As a result, the contact area of the sacrificial anode 76 with the seawater 10 is significantly larger (for example, 60
(About 70%). As a result, the consumption of the sacrificial anode 76 during the navigation of the ship 42 is reduced, and the life of the sacrificial anode 76 can be extended.

Further, in this embodiment, the sacrifice anode 116 during the navigation of the ship 42 is set by the above-described mounting position.
But naturally emerges above the sea surface. This will be described with reference to FIGS. When the ship 42 is navigating in the direction of arrow A in FIG. 7, the seawater 10 behind the stern skin 441 is eliminated by the hull 44, but the seawater 1
Since the speed at which the ship 42 travels is faster than the speed at which 0 enters, a region 10c in which the seawater 10 is depressed in a triangular shape is formed behind the stern outer plate 441 as shown in FIG. Therefore, as shown by the thick solid line in FIG. 6, the water level line 10b of the portion of the stern outer plate 441 during navigation is lowered to near the ship bottom, and the sacrificial anode 116 naturally comes out of the sea surface. As a result, the consumption of the sacrificial anode 116 can be prevented while the ship 42 is navigating, so that the life of the sacrificial anode 116 can be significantly extended.

As described above, sacrificial anodes 76 and 1
Since the service life of the ship 16 can be prolonged, the period of docking for replacing the sacrificial anode 76 or 116 of the ship 42 can be greatly extended. This is very advantageous, for example, when the ship 42 goes on a sea voyage, or when the ship 42 goes on a voyage to an area where there is no facility for mounting a large ship 42.

By the way, the boss 482 of the propeller 48
It is preferable to make the outer diameter uniform in the axial direction (longitudinal direction). In addition, it is preferable that the sacrificial anode 76 has an outer diameter that is uniform in the axial direction (longitudinal direction) and substantially equal to the outer diameter of the boss 482. In this case, the seawater 10 extruded by the propeller 48 is
Flows along the outer peripheral surface of the sacrifice anode 76, and the water flow separation hardly occurs near the outer peripheral surface of the sacrificial anode 76. Therefore, the action of the sacrificial anode 76 during the navigation of the ship 42 can be stabilized, and The efficiency of the propeller 48 is also improved.

When a propeller nut 74 is provided between the boss 482 of the propeller 48 and the sacrificial anode 76, the propeller nut 74 has a circular outer shape as shown in FIGS. Preferably, the outer diameter is approximately equal to the outer diameter of boss 482 and sacrificial anode 76. In this case, since the seawater 10 flows on the surface of the propeller nut 74 without being disturbed, the separation of the water flow near the outer peripheral surface of the propeller nut 74 can be prevented. Incidentally, the propeller nut 74 shown in FIG. 9 has two flat portions 741 and 742 for turning with a spanner at opposing portions, and after tightening the propeller nut 74 to the other propeller shaft 46, This flat portion 74
Arc structures 743 and 744 are put on 1 and 742, respectively, and they are fixed with countersunk screws 745 and 746, respectively.

When the sacrificial anode 76 is attached to the rear end of the propeller shaft 46 by the structure shown in FIG. 8, the intermediate portion 862 of the bolt 86 and the through hole 763 of the sacrificial anode 76 correspond to each other. Since the bolt 86 is tightened, metal contact between the bolt 86 and the sacrificial anode 76 can be reliably ensured by tightening the bolt 86. Moreover, the two packings 88 and 90 can prevent the seawater 10 from entering the metal contact portion. Also, bolt 86
Seawater 1 is inserted into the threaded portion of the propeller shaft 46 and the female screw portion 463 of the propeller shaft 46.
0 can be prevented from entering by the packing 88. As a result, electrical conduction between the sacrificial anode 76 and the propeller shaft 46 via the bolt 86 can be reliably ensured for a long period of time. Incidentally, when the electrical connection between the sacrificial anode 76 and the propeller shaft 46 is cut off, the shaft system 45 including the propeller 48 passes through the seawater 10 from the sacrificial anode 76.
The sacrificial anode 76
Their corrosion protection is lost.

FIG. 10 is a schematic view showing an electric anticorrosion device for a ship according to another embodiment of the present invention. Explaining mainly the differences from the cathodic protection device 56 shown in FIG. 1, the cathodic protection device 57 of this embodiment is different from the control circuit 64 shown in FIG.
Instead, the potential of the hull 44 with respect to the reference electrode 68 is
And a second control circuit 108 which controls the protective current I ₂ to be output from the DC power supply device 62 so that the positive side by the potential difference component E ₂ to a preset than the set value E ₁ of the potential of the control circuit 60 . Others are the same as in the case of the above-described cathodic protection device 56.

In this case, the reference electrode (second reference electrode) for detecting the potential of the hull 44 in the seawater 10 may be provided separately from the aforementioned reference electrode (first reference electrode) 68. As in this embodiment, one reference electrode 68 may be used in common, and this is economical.

The control circuit 108 calculates the difference between the potential of the hull 44 in the seawater 10 and the potential of the reference electrode 68 as shown in FIG.
And 4 of the subtraction circuit 110 for detecting a potential E _B, the control circuit 6
An addition circuit 112 for obtaining a potential E ₃ (that is, E ₁ + E ₂ ) obtained by adding the set potential difference E ₂ to the set potential E ₁ with respect to 0;
Subtraction circuit 11 for outputting a signal S ₃ which is proportional to the difference in search of the difference (i.e. E _B -E ₃₎ between the potential E _B and the potential E ₃
4, and a diode 115 to the signal S ₃ it outputs only if positive.

In this example, DC power supply unit 62 responds to signal S ₃ supplied from control circuit 108 and outputs anticorrosion current I ₂ proportional to the value. For example, if the direction of the potential E _B is large it is high and the difference therebetween than the potential E _3, signal S ₃ output from the subtracting circuit 114 is protective current I ₂ to be output from the DC power supply device 62 becomes a positive large value Therefore, the anticorrosion current flowing from the anode 66 to the hull 44 through the seawater 10 to the hull 44 increases, thereby lowering the potential of the hull 44, thereby reducing the difference. Potential E _B
Is lower than the potential E ₃ (ie, when the potential of the hull 44 is too low), the signal S ₃ output from the subtraction circuit 114 is output.
Becomes negative, which is blocked by the diode 115 and is not output. As a result, protective current I ₂ which is output from the DC power supply device 62 is zero, so that the potential of the hull 44 rises.

With such a configuration, the potential of the hull 44 in the seawater 10 is set to the set potential E ₁ in the control circuit 60.
, Ie, on the plus side by the set potential difference E ₂ from the potential of the shaft system 45. Setting preferred range of potentials E ₁ and setting the potential difference E ₂ in this case is the same as in the previous cathodic protection device 56.

[0077] Also by cathodic protection apparatus 57 of this embodiment, as in the case of the previous cathodic protection device 56, to lower the potential of the shafting enough to supply sufficient protection current I ₁ to the shaft system 45 Therefore, electrochemical corrosion of the propeller 48 can be effectively suppressed. Moreover, the potential of the hull 44 can be kept to the positive side by the potential difference E ₂ minutes to a preset than the potential of the shafting 45, it is possible to prevent excessive corrosion of the hull 44, through the seawater 10 from the hull 44 It is possible to prevent a current from flowing to the shaft system 45 in a liquid junction manner.

Also, in the case where this cathodic protection device 57 is used, the first sacrificial anode 76 and the second sacrificial anode 116 as described above are provided for the same reason as in the case of the cathodic protection device 56 described above. good.

Although the above description has been made with reference to an example of a ship having one shaft system 45 as one shaft, the present invention is not limited to such a ship. It can also be applied to shaft vessels. In that case, the DC power supply 58 for the shaft system, the control circuit 60,
The detection brush 72 and, if necessary, the sacrificial anode 76 may be provided for each shaft system.

[0080]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, the first DC power supply and the first control circuit for controlling the potential of the shaft system in seawater and the second DC power supply for controlling the potential of the hull in seawater are provided. 2
The DC power supply and the second control circuit, it is possible to sufficiently supply an anti-corrosion current to the shaft system and sufficiently lower only the potential of the shaft system, thereby preventing over-corrosion of the hull. In addition, electrochemical corrosion of the propeller can be effectively suppressed. As a result, the corrosion of the propeller, which has been considered impossible in the past, especially in the vicinity of the blade root, can be effectively suppressed by the cathodic protection device. as a result,
Even without providing cavitation holes as in the past,
The life of the propeller can be greatly extended. In addition, when the cavitation holes are not provided, the processing of the propeller becomes easy, and the thickness of the blade root portion of the propeller can be reduced, so that the propeller efficiency does not decrease.

Further, since it is not necessary to lower the potential of the hull similarly to the potential of the shaft system, it is not necessary to supply a large anticorrosion current to the hull through seawater from the second DC power supply.
The output power of the cathodic protection device can be saved, and the power consumption can be reduced accordingly.

In addition, the potential of the hull is controlled by the second control circuit to be on the plus side by a predetermined potential difference from the potential of the shaft system, so that the potential of the hull drops too much and the hull becomes excessive. Not only can corrosion prevention be prevented, but also it is possible to prevent a current from flowing from the hull to the shaft system through seawater to the shaft system due to an excessively large potential difference between the hull and the shaft system. As a result, it is possible to suppress the occurrence of local corrosion at the current outflow portion from the hull, and to prevent the liquid junction current from being supplied from the first DC power supply device. Accordingly, the output power of the first DC power supply can be saved.

According to the second aspect of the present invention, the first DC power supply and the first control circuit for controlling the potential of the shaft system in seawater and the second DC power supply for controlling the potential of the hull in seawater are provided. 2
Since the DC power supply device and the second control circuit are provided, the same effect as in the case of the cathodic protection device according to claim 1 can be obtained.

According to the third aspect of the present invention, since the first reference electrode and the second reference electrode are the same reference electrode, it is more economical than the case where both are provided separately. Further effects can be obtained.

According to the fourth aspect of the present invention, since the first anode and the second anode are the same anode, it is more economical than when both are provided separately. Can be played.

According to the fifth aspect of the present invention, the set potential in the first control circuit is set to a value between -980 mV and -1050 mV.
Since it is set within the range of mV, it is possible to obtain a further effect that a good anticorrosion effect on the propeller can be obtained without unnecessarily increasing the output power of the first DC power supply device.

According to the sixth aspect of the present invention, since the set potential difference in the second control circuit is set within the range of 80 mV to 120 mV, the hull is prevented from being over-corrosed and insufficiently protected, so that the hull can be properly protected. It is possible to obtain a further effect that not only can a great anticorrosion effect be obtained, but also a current can be suppressed from flowing from the hull through the seawater to the shaft system.

According to the seventh aspect of the present invention, the propeller shaft and the output shaft of the main engine are electrically insulated from each other by the insulator at the coupling portion. Leakage current can be completely prevented from flowing to the shaft system, so that when a potential difference is made between the hull and the shaft system, it is not necessary to apply extra energy to the shaft system. The further effect that the output current power of one DC power supply device can be saved can be obtained.

According to the eighth aspect of the present invention, the applying brush has a set of brushes which are arranged to face each other across the propeller shaft and are electrically connected in parallel to each other. The brush for use has a similar set of brushes, so that even if the propeller shaft oscillates, a negative potential can be stably applied to the shaft system and the potential of the shaft system can be reduced. A further effect that stable detection can be achieved.

According to the ninth aspect of the present invention, the first sacrificial anode is attached to the rear end of the propeller shaft, and the anticorrosion current can be supplied stably to the propeller through seawater. Even if disturbance such as pulsation occurs in the anticorrosion current supplied to the propeller through the seawater from the power supply type cathodic protection device, this disturbance is smoothed by the anticorrosion current from the sacrificial anode, and the anticorrosion current is supplied to the propeller stably. Therefore, a further effect that the electrochemical corrosion of the propeller can be suppressed more reliably can be achieved.

According to the tenth aspect of the present invention, the first
A hollow portion is provided inside the sacrificial anode, and a second sacrificial anode is provided at a position outside the hull of the ship and submerged in seawater while the ship is stopped and above the sea surface during navigation, While the boat is stopped, the first and second sacrificial anodes can supply an anticorrosion current to the shaft system and the hull, respectively, so that they can be prevented from being corroded. Its maintenance and management becomes very easy.

In addition, during the navigation of the ship, the interior of the cavity of the first sacrificial anode is evacuated to reduce the contact area of the sacrificial anode with seawater, so that the life of the sacrificial anode can be extended. Further, since the second sacrificial anode naturally comes out on the sea surface and its consumption can be prevented, the life of the sacrificial anode can be significantly extended.

According to this cathodic protection device, such further effects can be obtained.

According to the eleventh aspect of the present invention, the outer diameter of the boss of the propeller is made uniform in the axial direction, and the outer diameter of the first sacrificial anode is made uniform in the axial direction and the outer diameter of the boss. Since the diameter is almost equal, the seawater extruded by the propeller flows well along the outer peripheral surface of the sacrificial anode, so that water flow separation near the outer peripheral surface of the sacrificial anode is less likely to occur, and thereby, during the navigation of the ship The effect of the sacrificial anode can be stabilized, and the turbulence prevention can further improve the propeller efficiency.

According to the twelfth aspect of the present invention, since the intermediate portion of the bolt and the through hole of the first sacrificial anode are tapered corresponding to each other, the bolt and the sacrificial anode are formed at the tapered portion. Metal contact between the bolt and the propeller shaft by the first and second packings to prevent seawater from penetrating into the metal contact portion by the first and second packings. It is possible to prevent seawater from entering the sea. As a result, electrical conduction between the first sacrificial anode and the propeller shaft can be reliably ensured for a long period of time, so that the anticorrosion effect of the sacrificial anode can be stably secured for a long period of time. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an electric corrosion protection device for a ship according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a configuration of a first control circuit in FIG. 1;

FIG. 3 is a block diagram illustrating an example of a configuration of a second control circuit in FIG. 1;

FIG. 4 is a schematic view showing an example of the vicinity of a coupling of a propeller shaft.

FIG. 5 is a diagram illustrating an example of a configuration of a brush for application and a brush for detection.

FIG. 6 is a schematic diagram showing an example of the ship of FIG. 1 as viewed from the stern side.

7 is a schematic plan view showing an example of the vicinity of the stern of the ship shown in FIG. 1 during navigation.

FIG. 8 is a sectional view showing an example of the vicinity of the rear end of the propeller shaft.

FIG. 9 is a front view showing an example of a propeller nut.

FIG. 10 is a schematic view showing an electric anticorrosion device for a ship according to another embodiment of the present invention.

11 is a block diagram illustrating an example of a configuration of a second control circuit in FIG.

FIG. 12 is a schematic view showing an example of a conventional cathodic protection device for a ship.

[Explanation of symbols]

 Reference Signs List 10 seawater 42 ship 44 hull 45 axis system 46 propeller shaft 48 propeller 56, 57 cathodic protection device 58 first DC power supply 60 first control circuit 62 second DC power supply 64 second control circuit 66 anode 68 collation Electrode 70 Application brush 72 Detection brush 74 Propeller nut 76 First sacrificial anode 108 Control circuit 116 Second sacrificial anode

Claims (12)

(57) [Claims] 1. A first anode which is electrically insulated from a hull outside a hull of a ship and is submerged in seawater, and a first anode is provided with a positive potential relative to the first anode. A variable direct-current power supply device for applying a negative potential to a shaft system including a propeller shaft of a ship and a propeller attached thereto and supplying an anticorrosion current to the shaft system through seawater from a first anode; A reference electrode electrically insulated from the hull outside the hull of the ship and submerged in seawater, and the first and second reference electrodes are arranged so that the potential of the shaft system with respect to the reference electrode approaches a preset potential. A first control circuit for controlling an anticorrosion current output from the DC power supply device, and a second anode electrically insulated from the hull outside the hull of the ship and submerged in seawater; By applying a relatively positive potential to the second anode. A second direct-current power supply device that applies a negative potential relatively to the hull of the ship and supplies an anticorrosive current to the hull through seawater from the second anode, and a potential difference between the shaft system and the hull. And a second control circuit for controlling an anticorrosion current output from the second DC power supply so that the measured potential of the hull is on the plus side by a preset potential difference from the potential of the shaft system. Cathodic protection equipment. 2. A first anode mounted on a portion outside the hull of a ship and submerged in seawater while being electrically insulated from the hull, and applying a positive potential relatively to the first anode. A variable direct-current power supply device for applying a negative potential to a shaft system including a propeller shaft of a ship and a propeller attached thereto and supplying an anticorrosion current to the shaft system through seawater from a first anode; And a first reference electrode, which is electrically insulated from the hull at a portion outside the hull of the ship and submerged in seawater, and a potential of an axis system with respect to the first reference electrode is a preset potential. A first control circuit that controls the anticorrosion current output from the first DC power supply so as to approach
A second anode electrically insulated from the hull outside the hull of the ship and submerged in seawater;
A variable output second direct-current power supply for supplying a relatively positive potential to the anode of the vessel, a relatively negative potential to the hull of the vessel, and supplying an anticorrosion current to the hull through seawater from the second anode; A second reference electrode that is electrically insulated from the hull at a portion outside the hull of the ship and submerged in seawater,
The anticorrosion current output from the second DC power supply is set so that the potential of the hull with respect to the second reference electrode is on the plus side by a preset potential difference from the set value of the potential in the first control circuit. And a second control circuit for controlling the ship. 3. The apparatus according to claim 2, wherein the first reference electrode and the second reference electrode are the same reference electrode. 4. The apparatus according to claim 1, wherein the first anode and the second anode are the same anode. 5. The apparatus according to claim 1, wherein the set potential in the first control circuit is set in a range of −980 mV to −1050 mV. 6. The apparatus according to claim 1, wherein the set potential difference in the second control circuit is set within a range of 80 mV to 120 mV. 7. The propeller shaft is coupled via a coupling to an output shaft of a main engine that rotates the propeller shaft,
7. An electric ship ship according to claim 1, wherein an insulating member is provided at a portion of the coupling, and the propeller shaft and the output shaft are electrically insulated from each other by the insulating member. Anticorrosion equipment. 8. A brush for applying a negative potential relative to the shaft system from the first DC power supply device to the propeller shaft in the hull, and a detecting brush for detecting a potential of the shaft system. The brush is slidably in contact with the brush, and the application brush has a set of brushes that are arranged to face each other across the propeller shaft and are electrically connected in parallel with each other. The brush for use has a set of brushes arranged so as to face each other across the propeller shaft and electrically connected in parallel with each other.
8. The anticorrosion device for a ship according to 6 or 7. 9. A first sacrificial anode is attached to a rear end of the propeller shaft.
Or the anticorrosion device for a ship according to 8. 10. The vehicle according to claim 1, further comprising a second sacrificial anode mounted outside the hull of the ship and submerged in seawater when the ship is stopped and above the sea surface during navigation. The cathodic protection system for a ship according to claim 9, wherein the sacrificial anode has a cavity inside the rear part of the sacrificial anode. 11. The propeller has a boss having an outer diameter uniform in the axial direction, and the first sacrificial anode has an outer diameter uniform in the axial direction and substantially equal to the outer diameter of the boss. The ship's cathodic protection device according to claim 9. 12. A female screw having a male screw at the tip and a tapered intermediate portion extending toward the head, and a female screw portion screwed to the bolt is provided in the rear end of the propeller shaft. One of the sacrificial anodes is provided with a through hole which is tapered corresponding to an intermediate portion of the bolt, and the first sacrificial anode is fixed to the rear end of the propeller shaft with the bolt through the through hole. And a ring-shaped first packing surrounding the bolt is provided between the first sacrificial anode and the rear end surface of the propeller shaft, and the first sacrificial anode and the vicinity of the head of the bolt are further provided. 11. A ring-shaped second packing surrounding the bolt is provided between them.
Or the anticorrosion device for a ship according to 11.