JP3402061B2 - Ship - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] The present invention relates to an external power supply system.
For ships equipped with cathodic protection, more specifically
The improvement of the propeller blade shape. [0002] FIG. 8 is a schematic view showing an example of a conventional ship.
It is. The ship has a hull 14 and a sea outside the hull 14.
A propeller 18 provided in a part submerged in water 10
Is connected to the propeller 18 of the
A propeller shaft 16 that rotates in the
The propeller shaft 16 is rotatably supported in the vicinity of the propeller 18.
And the overhang bearing 24 is supported from the hull 14.
It has a bracket 26 to be held and a rudder 28. Professional
The prop 18 is composed of a boss 20 and a plurality of
And a blade (wing) 22. Further, this ship has a hull 14, a propeller shaft 1
6. Electricity of the anticorrosion target including the propeller 18 and the rudder 28
Cathodic protection with external power supply to prevent corrosion (electrochemical corrosion)
An apparatus 30 is provided. [0004] The cathodic protection device 30 has a variable output DC voltage.
Power supply device 32 and control for controlling this DC power supply device 32
The circuit 34 and the part submerged in the seawater 10 outside the hull 14
The anode 36 and the electrode 36 electrically insulated from the body 14
And a reference electrode 38, and the DC power supply 32
A positive potential relative to the anode 36, the hull 14, the propeller shaft
16, propeller 18, overhang bearing 24, rudder 28, etc.
A negative potential is collectively applied to the protected body
The anticorrosion electricity is applied to these protected objects from the pole 36 through the seawater 10.
The stream I is supplied. On the propeller shaft 16,
The brush 40, which serves both for applying potential and detecting potential, slides
Has been contacted. With such a configuration, the above-mentioned anticorrosion
Forcibly collectively apply to the body (for example, about -900 mV)
) By applying a negative potential to prevent corrosion of the body to be protected
Can be. [0005] SUMMARY OF THE INVENTION
An example of a conventional wing section is shown in FIG. Pressure surface 22 of blade 22
a should be almost flat as shown in this figure or very
Or a two-dot chain line a at the trailing edge
Washback is attached as shown on the back
22b is gentle, but larger than the pressure surface 22a side
It has an arc shape. The propeller 18 having such a blade 22
Is rotated in the seawater 10, the pressure surface 22a side becomes positive pressure.
And the back surface 22b side becomes negative pressure, and the sum of both pressures becomes thrust.
Become. In that case, generally, the negative pressure on the back surface 22b side is better.
It greatly contributes to the generation of thrust. Therefore, the thrust of the propeller 18 is increased.
In order to do this, the bend on the
It is conceivable to increase the negative pressure. But like that
Then, the peeling phenomenon of the seawater 10 is remarkable at the rear edge of the back surface 22b.
And cavitation occurred there,
A problem arises that the components are significantly corroded. Therefore
Conventionally, the bend on the back 22b side should be too large
Could not. On the other hand, the conventional longitudinal section of the propeller 18
An example is shown in FIG. The arrow A in FIG.
The arrow B indicates the direction of rotation, and the direction of thrust (ie,
Direction). The blade 22 is provided with a boss 20 as shown in FIG.
With respect to the central axis (i.e., the central axis of the propeller shaft 16).
They may be planted at right angles, or may be entirely constant (eg
For example, about 10 to 15 degrees).
In any case, the vertical cross section of the blade 22
It is wedge-shaped. The propeller 18 having such a blade 22
Rotates in the seawater 10, the blades 22 rotate the seawater 10.
Is scraped back to generate thrust, and the blades 22
In the vicinity of the pressure surface 22a side, the rotation of the blade 22 causes the sea
A large centrifugal force acts on the water 10 to generate a large lateral pressure P
You. When the lateral pressure P is large, the radial direction of the blade 22
The efficiency of the propeller 18 increases because more water flows escape in the direction
(Propeller efficiency) decreases. Also, due to the large lateral pressure P
Seawater 10 strongly strikes the bottom 14a (see FIG. 8)
Large vibration and noise on the hull 14
And the ride comfort is poor. Accordingly, the present invention provides a method for suppressing blade corrosion.
Thrust of the propeller can be increased and the propeller
Improved efficiency and reduced hull vibration and noise
The main purpose is to provide ships that can
You. [0013] According to the present invention, there is provided a ship
Shaft system including propeller shaft and propeller attached to it
To control the electric potential in seawater to a preset electric potential
Means and the potential of the hull in sea water
And a second means for controlling the potential difference to the plus side.
Equipped with an external power supply type anti-corrosion device
Adjust the pitch of each blade of the propeller from the leading edge to
Gradually increase as you approach the edge, and
The pressure side gradually increases from the blade root to the blade tip.
It is characterized by being bent. The pitch of each blade of the propeller is
When gradually increasing from the leading edge to the trailing edge (this
In this specification, this is marked
On the pressure side of each blade when the propeller rotates.
Negative pressure increases on the back side as positive pressure increases
Therefore, both work together to increase the thrust of the propeller. Further, each blade of the propeller is separated from its blade root.
If you gradually bend toward the pressure surface as you go to the wing tip
(This is referred to as a convergence angle in this specification), a professional
The water flow that is scraped out when the propeller rotates is near the center line of the propeller
Lateral pressure of the water flow decreases
This improves propeller efficiency and reduces hull
Vibration and noise are also reduced. However, as described above, each propeller blade
As mentioned above, the wing angle and the convergence angle give
Large negative pressure behind the trailing edge of the root and behind the wing tip
As a result, an area is created.
Bitation occurs and corrosion occurs there, and the propeller
Life is significantly shortened. On the other hand, the present inventor repeated experiments.
As a result, by improving the cathodic protection,
As described above, the potential of the hull is mainly
It will be on the plus side by a preset potential difference from the potential
Ship by being able to control
Not only for body corrosion protection, but also for each propeller blade
Corrosion does not occur on the propeller even if the purging and focusing angles are set.
That it can be effectively suppressed
Issued. The reason is as follows. That is, in a ship, the propeller
Relative water flow velocity is extremely high compared to other parts, and
The oxide film on the surface of the propeller is caused by cavitation.
Is stripped off by water hammer or underwater debris and becomes bare metal.
Propellers have a higher ionization tendency than other parts.
It is in a pan (ie, easy to mobilize) situation. Therefore, before
A conventional external power supply type anti-corrosion device as described
However, for the potential of the hull (for example, about -900 mV)
The propeller potential is highest (for example, -750 mV-
About 350mV), and through this seawater
To the lower potential, for example, rotatably supporting the propeller shaft.
Current may flow toward the overhanging bearing or hull.
You. This allows the propeller to act as a sacrificial anode.
This causes the propeller to undergo electrochemical corrosion.
You. In addition, as the speed of the ship increases, the propeller
Of the propeller is severe, so the electrochemical corrosion of the propeller
It becomes intense. [0019] Propeller corrosion has conventionally been cavitated.
Erosion due to water hammer was thought to be the major cause
However, as a result of various experiments, the inventor found that the propeller
Is a merger of electrochemical corrosion and water hammer erosion as described above
And that electrochemical corrosion is greater
Issued. In order to suppress the electrochemical corrosion of the propeller,
Pass the seawater from the anode to this easy-to-mobilize propeller
Provide sufficient anti-corrosion current to supply shaft seawater including propellers.
It turned out that it is sufficient to lower the potential inside. this
The potential is, for example, in the range of -980 mV to -1050 mV.
Is preferred. In that case, like a conventional cathodic protection device,
The potential of the entire body to be protected including the hull and shaft system
In the case of the control system, the area in seawater is smaller than that of the shaft system.
The very large hull becomes the subject of control, so the shaft system
Cannot be sufficiently reduced as described above.
No. Assuming that the potential of the entire body to be protected including the hull and shaft system, etc.
Can be very low, as described above,
The output power of the cathodic protection device
And the potential of the hull
If it falls too much, it becomes anticorrosion, the coating on the hull peels off,
Problems such as hydrogen embrittlement of the metals that make up the hull
Occurs. On the other hand, in the present invention, the potential of the shaft system is
First means for controlling and second means for controlling the potential of the hull
And provide sufficient anticorrosion current to the shaft system
Only the potential of the shaft system can be sufficiently lowered as described above.
You. As a result, while preventing over-corrosion of the hull,
Electrochemical corrosion can be effectively suppressed. Further, the potential difference between the shaft system and the hull is large.
If it becomes too high, one of the relatively high potentials (specifically,
The other is relatively low in potential from the hull (specifically, the shaft system)
The current flowing liquid through seawater cannot be ignored
This causes local erosion of the hull where current flows out.
Although there is a risk of eating, in the present invention, the second means
Therefore, the potential of the hull is lower than the potential of the shaft system.
It is controlled so that only the order difference is on the plus side.
The occurrence of such local corrosion can be suppressed. This
The potential difference is preferably in the range of 80 mV to 120 mV, for example.
No. [0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a ship according to the present invention.
It is a schematic diagram showing an example. FIG. 2 shows the side of the propeller in FIG.
FIG. FIG. 3 shows a certain half of the propeller in FIG.
It is a blade | wing sectional view of a radial part. FIG. 4 shows the propeller of FIG.
It is a longitudinal cross-sectional view. 8 to FIG.
The same reference numerals are given to the corresponding parts, and
Differences from the conventional example will be mainly described. In this embodiment, FIG. 2 and FIG.
As shown, each blade 22 of the propeller 18 as described above
In the direction from the leading edge to the trailing edge of the blade 22.
Is gradually increasing. In other words, the trailing angle H
You. For comparison, the shape of the conventional blade 22 shown in FIG.
Is indicated by a two-dot chain line b in FIG. 2 and FIG. This chasing angle H
Is attached to all the blades 22 by the same standard.
I have. When looking at each blade 22, the boss 20
From the root near the tip to the tip of the tip.
You. However, even if the purging angle H is added, the trailing edge of each blade 22
The wall thickness is not particularly increased, and the trailing edge is
It is streamlined. The propeller has a gradually increasing pitch.
Has been known for a long time,
The pitch gradually increases toward the end
Yes, with the addition of the purging angle H
Is gradually pitched from the leading edge to the trailing edge of the blade.
And both are completely different. Such an additional blade is attached to each blade 22 of the propeller 18.
When the shank angle H is added, referring to FIG.
Is rotated in the seawater 10, the seawater 10
Will be strongly scraped by the trailing edge of the pressure surface 22a
Then, the positive pressure on the pressure surface 22a side of each blade 22
Increased compared to propellers. As a result, the prope
The thrust of the la 18 increases. In addition, the sea water 10 is
At the rear edge of the rear face 22b of the
Therefore, the negative pressure on the back surface 22 b side of each blade 22
Increase compared to propellers. This allows the professional
The thrust of the prop 18 increases. In this propeller 18,
The combination of the two functions as described above, compared to the conventional propeller
All thrust increases. When generating the same thrust,
The diameter of the propeller 18 can be reduced compared to the example.
Therefore, the propeller 18 is brought close to the bottom 14a,
Professional for the direction of travel, specifically for the bottom 14a
The angle α (see FIG. 1) of the propeller shaft 16 can be reduced.
Wear. As a result, the direction of thrust generated by the propeller 18 and
Since the angle between the ship and the direction of travel is small,
The rate is improved. Further, the angle of attack β of each blade 22 (2 from the leading edge)
The angle with respect to the reference line on the back surface 22b side of up to about 5%. Figure
3) increases, the loss at the leading edge increases
However, even when the purging angle H is added as described above, each blade 22
The angle of attack β is small because the pitch of
Can be kept good. In other words, make the angle of attack β smaller
The pitch near the trailing edge can be set arbitrarily by the pursuit angle H
A wide speed range from low speed to high speed.
The propeller efficiency can be kept good over the surroundings. The purging angle H is higher for a high-speed ship.
Larger, smaller for slower vessels
New FIG. 5 shows a specific example of the method of determining the purging angle H.
It will be described in the light of the above. That is, the blade width of the blade 22 in the cross section is
When L (mm), distance x (mm) from the leading edge
At this point, the pressure surface 22a of the blade 22 is
Switch surface 62 (a unit representing the nominal pitch of propeller 18).
The distance H (mm) away from the pure spiral surface)
Is the angle, which, according to experiments, is in the range
It is preferable to set Where K₁= 0.005-
0.025, a = 2. The back surface 22b of the blade 22
As shown in FIG. 3, the shape substantially conforms to the pressure surface 22a.
Shape. [0032] ## EQU1 ## H = K₁L (x / L)^a Further, in this embodiment, as shown in FIG.
As shown, each blade 22 of the propeller 18 is
Toward the pressure surface 22a (in other words,
It is bent toward the rotation direction of the propeller 18). That is, focusing
The corner J is attached. For comparison, the prior art shown in FIG.
The shape of the propeller 18 is indicated by a two-dot chain line c in FIG. This
The convergence angle J of the plurality of blades 22 is the same
Attach as standard. However, even if the convergence angle J is added,
Do not increase the thickness of the wing tip in particular.
The wing tips maintain a streamlined shape. As described above, each blade of the propeller is
Is known to have a fixed inclination angle on the stern side
But this is to make a certain angle to the whole of each blade
Yes, with the convergence angle J
Gradually increases the angle from the wing root to the wing tip.
It is to make them bigger, and they are two completely different things. The blades 22 of the propeller 18 are
When the convergence angle J is given, referring to FIG.
8 is rotated in the seawater 10, the wing tip of each blade 22
The seawater 10 that is scraped out from the vicinity is the center of the propeller 18
It will be scraped diagonally toward the line side, this professional
The water flow scraped from the propeller 18 is inside the propeller 18
The conventional propeller can be squeezed toward the core.
The lateral pressure P of the water flow is reduced as compared with the case of FIG. This allows the feather
Water flow that escapes in the radial direction of the root 22 is reduced,
The efficiency of the prop 18 is improved. When the lateral pressure P becomes small, it is scraped out.
Seawater 10 is hit against the bottom 14a (see FIG. 1).
Since the force is reduced, noise and vibration generated on the hull 14 are reduced.
Movement becomes smaller. Further, the ship bottom 14a is located above the propeller 18.
There is nothing below, so the above lateral pressure P is
Normally, there is an imbalance above and below the propeller 18.
This causes vibration of the propeller 18.
You. Conventionally, since the lateral pressure P is large, the propeller 18
Vibration occurs, which propagates through the propeller shaft 16 and
Although a large vibration occurred in 14 as well, this implementation
In the example, since the lateral pressure P becomes small, such a propeller 1
In addition, the vibration of the hull 14 can be reduced. Therefore, according to this embodiment, the ship
Noise and vibration are very low,
Will be very good. The convergence angle J is larger in the case of a high-speed ship.
Larger, smaller for slower vessels
New FIG. 6 shows a specific example of how to determine the convergence angle J.
It will be described in the light of the above. That is, the blade length of the blade 22 is M (mm).
When the distance is x (mm) from the blade root,
The distance J (mm) away from the simple plane 64 is the convergence angle.
According to experiments, this is within the range represented by the following equation.
It is preferable to set. Where K_Two= 0.01-0.0
5, b = 2-3. The back surface 22b of the blade 22 is
As shown in FIG. 4, the shape substantially conforms to the pressure surface 22a.
I do. [0041] ## EQU2 ## J = K_TwoM (x / M)^b Next, the cathodic protection device will be described with reference to FIG.
To explain, the cathodic protection device 42 of this embodiment is
It is of a power supply type and has a propeller shaft 16 and
In seawater 10 of shaft system 15 including attached propeller 18
The potential E at a preset potential E₁First means for controlling
44 and the potential of the hull 14 in the seawater 10
Is also a preset potential difference E_TwoNo. to control to the plus side by the minute
2 means 46. The first means 44 is located outside the hull 14
Electrically insulated from the hull 14 at the part submerged in the water 10
The attached anode 36 and the anode 36 are relatively positive.
By applying a potential to the shaft system 15,
An anticorrosion current is supplied from the anode 36 to the shaft system 15 through the seawater 10.
A variable direct-current power supply 48 for supplying
Electricity is supplied from the hull 14 to the part outside and submerged in the seawater 10.
The reference electrode 38, which is electrically insulated and attached,
The potential of the shaft system 15 with respect to the electrode 38 is a preset potential E
₁Anti-corrosion output from the DC power supply 48 so as to approach
Style I₁And a first control circuit 50 for controlling The second means 46 comprises, in this example, the anode
36, and a relatively negative potential is applied to the hull 14.
An electric potential is applied to the hull 1 through the seawater 10 from the anode 36.
Output variable second DC power supply for supplying anti-corrosion current to power supply 4
56, and the potential difference between the shaft system 15 and the hull 14 is measured.
The potential of the hull 14 is set in advance to the potential of the shaft system 15.
Potential difference E_TwoDC power supply so that it is on the plus side
Corrosion protection current I output from 56_TwoControl times to control the
And a road 58. The anode is connected to a DC power supply 48.
(First anode) connected to the DC power supply 56
(The second anode) may be provided separately.
One anode 36 may be used as in the embodiment,
This will be economical. The anode 36 is, as in this embodiment, a propeller.
Preferably, it is provided near the la 18. Like that
If the propeller 18 is easy to activate,
0 can provide sufficient anticorrosion current
This is advantageous in suppressing the electrochemical corrosion of the propeller 18.
Because it becomes. The anode 36 is formed, for example, by depositing platinum on the surface of titanium.
It is plated. The reference electrode 38 is also
An electrode that is called and has a constant potential in seawater 10
An example is a silver chloride electrode. The propeller shaft 16 is provided inside the hull 14.
And a negative potential is generated from the DC power supply 48 relative to the shaft system 15.
The application brush 52 for application and the potential of the shaft system 15
The detection brush 54 for detection is slidably contacted.
Have been. A brush 52 for applying a potential and a brush 52 for detecting a potential
The brush 54 and the brush 54 are not shared with each other, as in this embodiment.
It is preferable to provide it separately. The reason is that the potential
A large space between the brush 52 and the propeller shaft 16 (for example,
Since the anti-corrosion current (of several A to several tens of A) flows, the voltage drop there
The lower part is large, and if both are used, this voltage drop
This is because a detection error is caused by affecting the potential detection of No. 5.
Apart from this embodiment, the detection brush 54 and the brush
Since almost no current flows between the propeller shaft 16 and the
The detection error due to the contact resistance in the above can be ignored. The above set potential E₁Is, for example, -980 mV
It is preferable to set within the range of -1050 mV. This
This is because the potential is too high on the plus side than -980 mV.
The anti-corrosion effect of propeller 18 is inferior, -1050 mV
The anti-corrosion effect of the propeller 18 is almost
Only the output power of the DC power supply 48 increases without increasing.
This is because it must be increased. The set potential difference E_TwoIs, for example, 80
It is preferable to set within the range of mV to 120 mV. This
When the voltage is less than 80 mV, the potential of the hull 14
The hull 14 too close to
On the contrary, if it exceeds 120 mV, the potential of the hull 14 rises
Not only does the anticorrosion effect on the hull 14 deteriorate
And liquid junction from the hull 14 through the seawater 10 to the shaft system 15
This is because the current that flows through cannot be ignored. In particular, when the material of the hull 14 is aluminum.
In this case, the set potential E₁To about -1000 mV, and
Set potential difference E_TwoIt is very preferable to set to about 100mV
Experiments confirmed that The overhang bearing 24, the bracket 26 and the rudder 2
8 is electrically connected in parallel to the hull 14 in this example.
So they are cathodically protected with the hull 14
You. However, a DC power supply for the rudder 28 and its control circuit
And the potential of the rudder 28 in the seawater 10 is
May be controlled separately from the above potential. The propeller shaft 16 is mounted inside the hull 14.
And is connected to the output shaft (not shown) of the main engine.
As described above, the potential difference E between the hull 14 and the shaft system 15 is obtained._Two
, The hull 14 and the shaft 1 via this main engine
It cannot be said that there is no risk of leakage current flowing between
To connect the propeller shaft 16 to the output shaft of the main engine.
Insulation is provided at the coupling part to provide complete electrical connection between the two.
It is preferable to insulate it. According to the above-described cathodic protection device 42,
The shaft system 15 has sufficient anticorrosion current I₁To supply power to the shaft system 15
Position can be lowered sufficiently,
It is possible to suppress the chemical corrosion very effectively. I
The potential of the hull 14 is set beforehand than the potential of the shaft system 15.
Potential difference E_TwoI can keep it on the plus side
Thus, it is possible to prevent the hull 14 from being over-corroded,
From the hull 14 through the seawater 10 to the shaft 15
The flow can be prevented from flowing. As a result, each blade 22 of the propeller 18
Even if the purging angle H and the convergence angle J as described above are added,
Effective suppression of corrosion of the rotator 18
Can be. It should be noted that the external power supply type electric protection
In addition to the food device 42, for example, as in the embodiment shown in FIG.
In the vicinity of the rear end of the propeller 18, the propeller shaft 16
It is preferable to attach a sacrificial anode 60 to the rear end of the
No. The sacrificial anode 60 is made of, for example, aluminum, zinc, or the like.
Or an alloy containing magnesium as a main component.
Quality, size, etc. depend on environmental conditions and anticorrosion specifications, as well as control circuits
Set potential E at 58₁As appropriate according to the value of
Good. As described above, the sacrificial anode 60 is connected to the propeller shaft 1.
By attaching to the rear end of this sacrificial anode 6
Stable anticorrosion electricity from 0 to the propeller 18 through the seawater 10
External power supply system
More specifically, the direct current power supply
From the device 48 through the seawater 10 to the shaft system 15
Even if disturbance such as pulsation occurs in the eddy current, this disturbance is
Smoothing by the anticorrosion current from 60
The anticorrosion current can be supplied stably. The result
As a result, the electrochemical corrosion of the propeller 18 is more reliably suppressed.
be able to. FIG. 7 shows another example of a ship according to the present invention.
FIG. The embodiment of FIG.
Only the configuration is different. Therefore, the differences are mainly discussed.
For clarification, the cathodic protection device 42 of this embodiment is shown in FIG.
Instead of the control circuit 58
The potential of the body 14 is equal to the potential set value E in the control circuit 50.
₁Potential difference E set in advance_TwoOnly be on the plus side
Protection current I output from DC power supply 56_TwoControl
A second control circuit 59 for controlling the BR is provided. Other
Is the same as in the case of the above-described cathodic protection device 42. With the cathodic protection device 42 of this embodiment,
Also, as in the case of the cathodic protection device 42 of the previous embodiment,
System 15 has sufficient anticorrosion current I₁To reduce the potential of the shaft system.
Can be reduced to the
Corrosion can be suppressed very effectively. Moreover,
The potential of the hull 14 is higher than the potential of the shaft system 15
Difference E_TwoThe hull can be kept on the plus side
14 can be prevented, and the hull 14
Current flows from the seawater 10 to the shaft system 15 in a liquid junction
Can be prevented. In all of the above, the shaft system 15 is one
Although a single-axis ship has been described as an example, the present invention relates to such a ship.
However, the present invention is not limited to this.
Of course, the present invention can also be applied to other ships. In that case, each
The above-described purging angle H and convergence angle J are applied to the blades 22 of the shaft system.
And, in the cathodic protection device 42,
DC power supply 48, control circuit 50, application brush 52
And a detection brush 54, if necessary, a sacrificial anode.
What is necessary is just to provide 60 in each axis system, respectively. [0062] As described above, according to the present invention, the prope
The pitch of each blade of the blade from the leading edge to the trailing edge of the blade
The pressure side of each blade
And the negative pressure on the back side
Too much, the two together increase the thrust of the propeller. When generating the same thrust,
Reduce the propeller diameter compared to the example and lower the propeller
Approaching the angle of the propeller axis to the ship's
Thrust generated by the propeller because it can be reduced
Angle between the ship's direction and the ship's
Efficiency is improved. Furthermore, even if the angle of attack is reduced,
The pitch near the trailing edge of the blade
Over a wide speed range from low to high
Thus, good propeller efficiency can be maintained. Further, each blade is moved from its root to its tip.
Is gradually bent to the pressure side according to
The water flow scraped out of the propeller is on the center line side of the propeller.
Can be squeezed toward the water, compared to conventional propellers.
The lateral pressure of the stream is reduced. As a result, escape in the radial direction of the blade
Propeller efficiency is improved due to reduced water flow. Also, when the lateral pressure was reduced,
Because the force against which seawater is hit to the bottom of the ship becomes smaller, the hull
The noise and vibration generated at the time are reduced. Further low lateral pressure
As it gets smaller, the unbalanced force acting on the propeller becomes smaller
Therefore, reduce the vibration of the propeller and hence the hull.
Can be. As a result, noise and
Vibration is very small and ride comfort is very good
You. In addition, the propeller shaft and its attachment
Preset potential in seawater of shaft system including installed propeller
First means for controlling the potential of the hull in seawater,
Position is controlled to the plus side by a preset potential difference from the axis system.
An anticorrosion device having second means for controlling
Therefore, the potential of the hull is lower than the potential of the shaft
Control so that only the potential difference set in advance is on the plus side.
Control of the ship's hull,
Add the purging and focusing angles described above to each blade of the propeller.
Effective control of corrosion on the propeller
can do. As a result, the life of the propeller is extended
Can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an example of a ship according to the present invention. FIG. 2 is a side view of the propeller in FIG. FIG. 3 is a wing sectional view of a certain radius portion of the propeller in FIG. 1; FIG. 4 is a longitudinal sectional view of the propeller in FIG. FIG. 5 is a diagram for explaining a specific example of how to determine the purging angle. FIG. 6 is a diagram illustrating a specific example of how to determine a convergence angle. FIG. 7 is a schematic view showing another example of a ship according to the present invention. FIG. 8 is a schematic view showing an example of a conventional ship. FIG. 9 is a wing cross-sectional view of a certain radius portion of the propeller in FIG. 8; FIG. 10 is a longitudinal sectional view of the propeller in FIG. [Description of Signs] 10 Seawater 14 Hull 15 Axis system 16 Propeller shaft 18 Propeller 20 Boss 22 Blade 22a Pressure surface 22b Back surface 42 Corrosion protection device 44 First means 46 Second means

Claims (1)

(57) [Claim 1] First means for controlling a potential in seawater of a shaft system including a propeller shaft and a propeller attached thereto to a preset potential, and A second means for controlling the potential of the hull to the plus side by a preset potential difference from the shaft system, and an externally-powered type cathodic protection device, wherein the pitch of each blade of the propeller is A ship characterized in that the number of blades is gradually increased from the leading edge to the trailing edge, and each blade is gradually bent toward the pressure surface from the blade root toward the blade tip.