WO1995023088A1

WO1995023088A1 - Propeller for boats and ships

Info

Publication number: WO1995023088A1
Application number: PCT/FI1995/000099
Authority: WO
Inventors: Jukka Kalevi Pohjola
Original assignee: Jukka Kalevi Pohjola
Priority date: 1994-02-23
Filing date: 1995-02-23
Publication date: 1995-08-31
Also published as: FI940840A0; FI95226B; AU1710995A; FI95226C

Abstract

This invention relates to a propeller for boats and ships, and more particularly, to a propeller which produces a higher thrust for a given power input. The higher thrust and efficiency of the propeller is based on the fact that the water slip existing in present propellers has been totally eliminated. This kind of effect can be obtained when the propeller is constructed so that when viewed parallel to the axis all the blades (2) are tangent to each other, and in front elevation view the blades are located helically on the hub (1) so that there is a small gap (3) between the blades. The gaps enable water to flow between the blades so that each blade can function individually without interfering with the functioning of the other blades.

Description

PROPELLER FOR BOATS AND SHIPS

This invention relates to a propeller for boats and ships. This new propeller can in principal be used in all marine vessels where presently known screw propellers are used. The main embodiment of the propeller comprises a cylindrical hub which is provided with fixed blades. This new invention differs mainly from the embodiment of present screw propellers in the respect that the blades have been attached on the hub in helicoidal pitch so that the blade following the former blade has been located behind the former blade on the pressure side so that when viewed parallel to the axis the symmetrical blades which resemble a sector of a circle are tangent to each other so that the angles of the sectors form the angle of a full circle 360°. The functioning of this kind of propeller compared to present screw propellers is based on the fact that there doesn't exist any "empty space" between the blades and so there doesn't exist any water slip either. Water slip is precisely the worst factor which reduces propeller efficiency in present propellers, so the inventive propeller has a higher propeller efficiency than any presently used propeller^' which has a propeller efficiency a little over 70 % at the maximum. In practice the propeller efficiency of present propellers is however much less especially in ships carrying heavy loads when the propeller efficiency can be only about 20 - 30 % mainly due to the great slip. The inventive propeller can achieve a propeller efficiency which is even more than 90 % and the propeller efficiency remains almost constant even with heavy loads since there doesn't exist any slip in the propeller. The inventive propeller thus saves energy considerably or respectively increases the speed of a ship.

Man has tried several times to use the over 2 000 years old Archimedes screw as a so called continuous screw propeller. This propeller has however never functioned properly. The reason for the bad functioning of this propeller is clarified when it is compared to the inventive propeller with a very similar structure. In a continuous screw propeller the water mass entering the blade must partly rotate around the axis and the replacing water can enter the blade partly only from side directions instead of coming along the leading edge of the blade. This "rotating" of the water mass and the turbulence waste a lot of energy. The inventive propeller could be called a partly continuous screw propeller since each blade "takes and leaves" the entering water mass as linearly as possible

SUBSTITUTE SHEET so that the "rotating" of the water mass and the turbulence consume a minimum amount of energy. This causes correspondingly a maximum propeller efficiency.

The propellers presently in use are also screw propellers and the first versions of them were developed hundreds of years ago when the good properties of the Archimedes screw and the windmill were combined. In the beginning the propeller efficiencies were very modest, but even with present techniques the available maximum propeller efficiency is at most about 70%. The low propeller efficiency is mainly caused by the "compulsory empty space" between the blades and the water slip which is due to these empty spaces. The amount of slip is generally over 20 % of the shaft power between the blades. Attempts to reduce the water slip have been made by building tunnels around the propeller; by building rotating propeller blades and by installing on the shaft two in different directions rotating propellers. These maneuvers have often led to slightly better results, but the propeller efficiency has still remained low and the investment costs have increased. In the inventive propeller there doesn't exist any water slip at all and so the propeller efficiency is only reduced by different flow resistances and cavitation. The total influence of these energy losses is however rather small since their energy consumption is generally only about 4 - 8 % of the shaft power. This means that by using the inventive propeller propeller efficiencies which are over 90 % can be obtained.

The accompanying drawings illustrate the inventive propeller in which:

FIG. 1 is a side view of a four blade propeller.

FIG. 2 illustrates a projected figure of the former propeller when it is viewed parallel to the axis. In order to make the figure clearer the propeller blades have been separated from each other by two lines instead of one. FIG. 3 is a projected figure of a six blade propeller when the blades have been designed hydrodynamically better than the blades resembling sectors of a circle.

Figure 1 illustrates a side view of a four blade propeller. The body of the propeller comprises a firm cylindrical fixed hub 1 . Four fully symmetrical propeller blades 2 resembling sectors of a circle have been

SUBSTITUTE SHEET welded or otherwise very firmly attached on the surface of the hub 1 in a helicoidal position vertically to the axis. The blades 2 have been set on the hub 1 in a certain desired pitch so that when viewed parallel to the axis all the blades 2 are tangent to each other i. e. the sectors of the blades form a full circle 360°.

When the propeller is viewed tangentially along the surfaces of the blades 2 a small gap 3 with the size of approx. 3 to 4 times the average thickness of the blade 2 is left between the blades. These gaps 3 form an essential feature for the whole functioning of the propeller since the gaps 3 enable each blade 2 to function fully independently so that no propulsion disturbance is caused by the other blades. In figure 1 the mentioned gaps 3 divide the propeller into a four blade propeller. The highest possible propeller efficiency is achieved with the co-operation of all the blades. The propeller can be constructed so that it has 3 blades, but rather 4 or 5 blades and when the hub 1 diameter is big more blades can be installed.

Figure 2 illustrates the projected figure of the propeller when it is viewed parallel to the axis. In order to make the figure clearer the propeller blades 2 have been separated from each other by drawing two lines. In the center of the hub 1 there is a cylinder 4 for attaching the propeller onto the axis. The blades 2 of the propeller have been marked so that the first blade is 2a and the next ones 2b, 2c and 2d.

The operation of the inventive propeller is based on three main principles which are clarified in the following:

1 . The blades 2 of the propeller always take free water and they also push the free water they have taken into free water. This means in practice that none of the vertical pressure wave vectors of any differential surface of any blade 2 hit the inner surface of other blades. Due to the helicoidal structure of the propeller such a situation can occur only in connection with the first and the last blade. Such a situation can however be easily eliminated by making the distance between the first blade 2a and the last blade 2d large enough. In figure 1 vector v presents a pressure wave vector which clearly passes the last blade 2d. This always happens when the front

SUBSTITUTE SHEET edge of the first blade and the rear edge of the last blade is greater than the diameter of the propeller.

2. When the propeller is viewed parallel to the axis all the blades 2 are tangent to each other i. e. the sum of the angles of the sectors formed by the blades is 360°. In practice this means that the propeller has a maximal blade area for pushing water along the whole pitch since there doesn't exist any empty space between the blades. Thus no water slip occurs and the propeller efficiency is reduced only by flow resistances and cavitation. Their effect especially in low r.p.m. s is relatively small and so the propeller efficiency can be over 90 %. An essentially important feature of the propeller is the fact that even if the r.p.m. s of the propeller are raised the propeller efficiency stays almost constant. Then the often very low propeller efficiencies of heavy cargo ships can even be doubled.

3. The total operation of the propeller is formed by the collaboration of the separate blades 2a, 2b, 2c and 2d which work independently without interfering with each other's functioning. This activity has been achieved in the propeller by installing the blades 2 on the hub 1 helicoidally so that the blade following the former blade has been located behind the former blade on the pressure side so that between the blades there is a small gap 3 through which water can flow. At the position of gap 3 the former blade stops functioning and correspondingly the next blade starts functioning by taking new water onto the blade.

When the ship starts moving the rotating propeller causes a flow in the water which creates a thrust on the blades of the propeller. The amount of this thrust depends on the diameter, pitch and r.p.m. of the propeller and the amount is proportional to the weight of the water mass pushed ahead per a unit of time. In addition the propeller is hit by a force which is dependent on the internal resistance of water flow coming from the propeller. Per each revolution the inventive propeller pushes water which creates a cylindrical water statue the bottom of which is formed by the projected area of the propeller (figure 2) and the length of which by the pitch of the propeller. If the present screw propeller had the same pitch and diameter as the former propeller and if between the blades there were empty space half of that of the former propeller it would

SUBSTITUTE SHEET form a similar water statue the volume of which would be only half as large Correspondingly the thrust would also be half as large In practice propeller blades resembling sectors of a circle are not the best possible ones and due to the rotating motion a better propeller efficiency is achieved when the blades are shaped hydrodynamically so that the entire front edges of the blades cut water while the projected area of the blades covers as great a part as possible of the propeller's rotation area. This kind of blades 5 have been presented in figure 3.

SUBSTITUTE SHEET

Claims

A ship and boat propeller on the cylindrical hub ( 1 ) of which three, four or more symmetrical propeller blades (2) have been installed in a certain pitch helicoidally so that in a side view between the blades there is a gap (3 ) which is 3 - 4 times as thick as the propeller blade wherein when viewed along the axis all propeller blades are tangent to each other so much that the hydrodynamically shaped blades (5) cover an essential part of the rotation area of the propeller and in which the distance between the first blade (2a) and the last blade (2d) is larger than the diameter of the propeller so that none of the vertical pressure wave vectors of any differential surface of the first blades hit the inner surface of the last blades.

SUBSTITUTE SHEET