EP0648670A1

EP0648670A1 - Propulsion system

Info

Publication number: EP0648670A1
Application number: EP94850180A
Authority: EP
Inventors: Leif Magnus Endresen
Original assignee: Servogear AS
Current assignee: Servogear AS
Priority date: 1993-10-18
Filing date: 1994-10-14
Publication date: 1995-04-19
Anticipated expiration: 2014-10-14
Also published as: ATE162146T1; EP0648670B1; NO178103C; AU7591294A; NO933744D0; NO933744L; DE69407918D1; NO178103B

Abstract

Propulsion system, particularly for high-speed boats (5), consisting of a propeller (3) having a propeller hood (4') positioned downstream relative to the propeller blades, and a rudder (7'), and where the propeller hood (4') extends entirely or partially along the lower edge of the rudder (7'), and where the rudder has approximately the same cross section as an airfoil or aircraft wing. The propeller hood is preferally designed as a cone or as a rotating body the generatrix of which forms a curve.

Description

The present invention relates to a propulsion system, particularly for high-speed boats, consisting of a propeller having a propeller hood positioned downstream relative to the propeller blades, and a rudder.
The present invention is particularly suitable for use in connection with a propulsion system wherein an inclined propeller shaft is employed. This should not, however, be seen as a limitation to the application of the invention.
In a conventional propulsion system as shown, for example, on the attached Figures 1, 2 and 3, particularly for high-speed boats having an inclined propeller shaft 1, the propeller shaft is suspended in a bracket 2, and the propeller itself 3 terminates in a propeller hood 4. Propeller shaft 1 is angled relative to the boat hull 5 at an angle of α relative to the structural water line 6 of the boat.
The boat rudder 7, as shown on Figure 1, is positioned downstream in relation to both the propeller blades 3 and the actual propeller hood 4. Rudder 7 has a streamlined configuration, i.e., having an outwardly curved surface on each side thereof.
At high speeds suction will be generated at the after edge of propeller hood 4. Such suction will substantially reduce the effect of propeller 3. The propeller will also establish rotation in the slip stream behind the propeller. This, too, represents a significant power loss. Such rotational loss may be partially recovered in the rudder.
The present invention therefore aims to reduce or eliminate the suction behind the propeller hood, at the same time as it seeks to improve the rudder effect with respect to recovery of rotational loss behind the propeller.
According to the invention, therefore, the propulsion system mentioned in the introduction above is characterized in that the propeller hood extends entirely or partially along the lower edge of the rudder, and that the rudder has approximately the same cross section as an airfoil or aircraft wing.
According to an embodiment form of the propulsion system, the propeller hood is shaped like a cone. Alternatively, the propeller hood may be designed as a rotating body the generatrix of which forms a curve.
The invention will now be described in more detail with reference to the appended drawings.
Figure 1 is a view of a propulsion system according to the prior art.
Figure 2 is a view of section II-II in Figure 1.
Figure 3 is an elevational end view of section III in Figure 1.
Figure 4 is a side view of the propulsion system in accordance with the present invention.
Figure 5 is a view of section V-V in Figure 4.
Figure 6 is an elevational view of section VI in Figure 1.
Figure 4 illustrates the way propeller shaft 1 extends from a sleeve bearing 8 in the hull 5, similarly to what is also shown in Figure 1. In the depicted embodiment, propeller shaft 1 is mounted in a propeller bracket or sleeve bearing 2 in the same manner as illustrated in connection with Figure 1. As in Figure 1, the propeller is designated with reference numeral 3. The actual propeller hood, according to the invention, is preferably cone shaped, and is indicated by reference numeral 4'in Figures 4 and 5. The rudder extending downward from boat hull 5 is indicated by reference numeral 7. This rudder is specially designed to have the approximate cross section of an airfoil or aircraft wing, imparting rudder 7' with a pressure side 8 and a suction side 9.
In the known solution, as indicated in Figure 2, a rotating slip stream 10 is generated behind the propeller, and this has a detrimental effect on the overall effect of the propulsion system.
As will be apparent from Figure 4, propeller hood 4' extends completely or partially along the lower edge of rudder 7'. As mentioned above, the rudder will have approximately the same cross section as an aircraft wing or airfoil. The slip stream produced behind the propeller will rotate in the same rotational direction as the propeller, as shown inter alia by Figure 6. This will in turn cause the water stream to impact rudder 7' at a slant. The rudder thus acquires a pressure side 8 and a suction side 9 when set at its center position, as shown in Figures 5 and 6. The overpressure on the one side may be increased if the rudder is designed as shown, i.e., like an airfoil or aircraft wing. This pressure will be transmitted down to propeller hood 4'. As a result of the pressure difference, water will flow around propeller hood 4' to the suction side 9 of the rudder. This will then increase the pressure around the entire propeller hood 4'. The suction that would be generated against the propeller hood in accordance with the known art would be partially or completely eliminated according to the present invention.
The circulation around the propeller hood will have the opposite direction of rotation as the slip stream behind the propeller. This will have the result of counteracting turbulence, thereby decreasing the power loss. Propeller 3 will thereby achieve a greater thrusting power, which may be utilized to attain higher speed or a lower power consumption.
The forces generated against the rudder could be equalized by having a propeller rotating in the opposite direction on twin-propeller boats, or by rotating the rudder sections above the propeller, thus counterbalancing the steering forces on boats having one propeller.
As will be apparent from Figure 4, a small clearance k between propeller hood 4' and rudder 7' will be necessary to permit rudder 7' to move relative to the rotating propeller hood 4'.
As will be apparent from Figure 5, the motion of slip stream 10' will be more rectilinear than the rotation that occurs in the embodiment shown in Figure 2.
In Figure 6 the water circulation below rudder 7' is designated by reference numeral 11, and reference numeral 12 indicates the direction of rotation of the propeller.
The present propulsion system has proven during testing that it is possible to achieve power gains of a magnitude of between 10% and 15% compared with the known art, cf. Figures 1-3.

Claims

A propulsion system, particularly for high-speed boats (5), consisting of a propeller (3) having a propeller hood (4') positioned downstream relative to the blades of the propeller (3), and a rudder, characterized in that the propeller hood (4') extends entirely or partially along the lower edge of the rudder (7'), and that the rudder has approximately the same cross section as an airfoil or aircraft wing.
A propulsion system as disclosed in claim 1,
characterized in that the propeller hood (4') is shaped like a cone.
The propulsion system as disclosed in claim 1,
characterized in that the propeller hood (4') is designed as a rotating body the generatrix of which forms a curve.