JPS599999Y2 - Root erosion prevention device - Google Patents

Description

[Detailed description of the invention] This invention eliminates root erosion that occurs at the root of the propeller blade during high-speed rotation by installing a split ring plate with guide vanes fixed to the outer periphery of the shaft bracket that supports the propeller shaft in front of the propeller. This invention relates to a device that effectively prevents.

Root cavitation occurs in the blade roots of the astern plane of high-speed propellers installed on high-speed boats, and due to the erosion caused by this, the lifespan of the propeller is short, 2 to 4 years.

This invention was proposed to address these problems and to prevent root erosion by suppressing the occurrence of root cavitation on the trailing surface of the propeller blade.
A plurality of small-diameter guide vane roots are radially fixed to the split ring plate attached to the outer periphery of the shaft bracket that supports the propeller shaft in front of the propeller, with the roots tilted in the direction opposite to the pitch direction of the propeller with respect to the axial direction. To provide a root erosion prevention device characterized in that the angle of inflow water to the propeller is changed to reduce the angle of attack at the root of the propeller blade, thereby suppressing the occurrence of cavitation at the root of the propeller blade.

An embodiment in which the device of the present invention is installed in a high-speed boat will be described below with reference to the drawings.

In Figures 1 to 5, 1 is the bottom of the high-speed boat, 2 is a shaft bracket for supporting the propeller shaft attached to the bottom 1, 3 is the propeller shaft supported by the shaft bracket 2, and 4 is the rear of the propeller shaft 3. 5 is a propeller blade attached to the end; 6 is a rudder attached to the rear of the propeller 4; 7 is a ring of the device of the present invention attached to the rear of the shaft bracket 2 and in front of the propeller 4. Plate 8 is a guide vane fixed to ring plate 7.

The root erosion prevention device in this embodiment has a second root erosion prevention device.
As shown in the figure and FIG. 3, a plurality of guide vanes 8 are provided on each of the two-part semicircular ring plate pieces 7a and 7b, and are inclined by θ with respect to the axial direction in a direction opposite to the pitch direction of the propeller. They are fixed in a radial pattern.

The two ring plate pieces 7a and 7b are attached to the propeller shaft 3.
They are held together and held together, and also serve as general guard rings.

FIG. 4 shows the expanded positional relationship between the propeller 4 and this device, and the operation of this device will be explained based on FIGS. 4 and 5.

In the figure, ■ is the propeller inflow water velocity.

The propeller blade 5 is moving in the circumferential direction at a speed of 2πnr in a portion having a radius r.

Note that n is the number of revolutions of the propeller.

The direction of the inflow water is changed by θ' by the guide vanes 8 of this device, and the direction of the inflow water is changed by Vr' in the same direction as the direction in which the propeller travels.
It has a certain velocity of vh in the axial direction.

θ′ is the angle at which the water flow is twisted by the guide vane 8 which is inclined by θ with respect to the axial direction.
Since no twist is given, θ' becomes θ.

FIG. 5 illustrates the difference in the angle of attack before and after the device is attached to the propeller blade 5.

Before installation, the angle of attack α is becomes.

Here, p indicates the pitch of the propeller. After installation, angle of attack α
′ becomes, and therefore, the angle of attack is reduced by this device as follows.

By installing this device in this manner, it is possible to reduce the angle of attack of the propeller blade root, thereby reducing the negative pressure on the backward advancing surface of the propeller blade root, suppressing the occurrence of cavitation, and preventing erosion.

In this embodiment, 12 guide vanes 8 are provided, but the number of guide vanes is determined from the viewpoint of the necessity to form a water flow uniformly inclined by θ' around the entire circumference of the propeller inflow part. If it is too small, the flow will be non-uniform, and if the chord length of the guide vanes is increased to prevent this, the resistance will increase and the propulsion efficiency will decrease.

Moreover, if there is too much, each blade becomes small, which causes problems in terms of strength and manufacturing.

From these viewpoints, the number of guide vanes is preferably 8 to 16.

In addition, the diameter of the propeller boss is generally designed to be approximately 0.2 times the diameter D of the propeller blade, and the diameter of the guide vane should be shorter considering the propulsion performance of the propeller, and root erosion. Considering the area of occurrence of
It is desirable to set it in the range of 0.3 to 0.5 D.

That is, it is preferable that the blade length L of the guide vane is 5 to 15% of the propeller diameter D.

Furthermore, the greater the inclination angle θ in the direction opposite to the pitch direction of the propeller, the better the cavitation suppression effect, but in a typical airfoil, it stalls at 15 to 20 degrees.
The flow is disrupted.

Therefore, θ may be 20° or less, preferably 5 to 20°, and more preferably 10 to 15°.

As described above, the device of the present invention installs a plurality of small diameter guide vanes in the axial direction of the propeller on the split ring plate 1 attached to the outer periphery of the shaft I bracket that supports the propeller shaft in front of the propeller. It is tilted in the opposite direction to the pitch direction and fixed radially, changing the propeller inflow water angle to reduce the angle of attack at the propeller blade root, thereby reducing the negative pressure on the trailing surface of the propeller blade root and preventing cavitation at the propeller blade root. The propeller is designed to suppress the occurrence of this, thereby extending the life of the propeller, and does not require any processing on the propeller body, and can be easily installed on existing boats.

[Brief explanation of drawings]

Figures 1 to 3 show an embodiment of the device of the present invention.
The figure is an elevation view showing the rear bottom of a high-speed boat equipped with the above-mentioned device, Figures 2 and 3 are elevational views and plan views showing the above-mentioned device enlarged, and Figure 4 is a propeller and FIG. 5 is an exploded view showing the positional relationship with the device of the present invention, and is an explanatory diagram showing changes in the angle of attack of the propeller due to attachment of the device of the present invention. 1...Bottom, 2...Shaff L~Bracket, 3...
・Propeller shaft, 4... Propeller, 5... Propeller blade, 6... Rudder, 7... Ring plate, 8... Guide vane, θ... Inclination angle of guide vane 8, L ...Blade length of guide vane 8.

Claims (1)

[Scope of utility model registration request] A plurality of small-diameter guide vanes are radially fixed to the split ring plate attached to the outer periphery of the shaft bracket that supports the propeller shaft in front of the propeller, and are tilted in the opposite direction to the pitch direction of the propeller with respect to the axial direction. A root erosion prevention device characterized by reducing the angle of attack at the propeller blade root by changing the inflow water angle to suppress the occurrence of cavitation at the propeller blade root.