GB1588123A

GB1588123A - Ships'rudders

Info

Publication number: GB1588123A
Application number: GB4400076A
Authority: GB
Original assignee: Hydroconic Ltd
Current assignee: Hydroconic Ltd
Priority date: 1977-10-24
Filing date: 1977-10-24
Publication date: 1981-04-15

Description

(54) IMPROVEMENTS IN SHIP'S RUDDERS (71) We, HYDROCONIC LIMITED, a British Company of Shipdesine House, Ramsey, Isle of Man, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to ship's rudders.

When a rudder is turned it develops sideways lift by virtue of being at an angle to the incident flow. Rudders generally speaking are symmetrical airfoil or hydrofoil sections because they have to go equally to port and to starboard.

An aircraft wing is cambered; in other words, it is not symmetrical about a nose-tail line but more of it lies to one side than to the other. The effect of this is much to increase the lift coefficient. A purpose of the invention is to apply this lift principle to ships' rudders in a way that has not hitherto been proposed.

In the decade 1860 to 1870, a considerable number of rudders were fitted to navel and merchant ships in Great Britain and elsewhere originating from the designs of a Mr.

Lumley. These rudders has a hinged trailing edge flap and this trailing edge flap was moved, as the rudder turned through an angle, to a greater angle than the rudder by the means of a sliding linkage attached to the top of the rudder. When the rudder was hard over at say 40 it was possible for this flap on the trailing edge of the rudder to be at 90 .

This did not, of course, divert the water through 90 but changed the downwash angle from the rudder appreciably, increasing it and obtaining more lift by virtue of the effective camber so achieved. This device has been used in modern times by a number of designers and there is nothing new in it, the originator being Lumley.

According to the present invention, there is provided a rudder on a ship comprising a rigid single-bladed main body with a hydrofoil section which is symmetrical about a central vertical plane extending from its leading to its trailing edge said main body being mounted to turn about a first vertical axis which lies in said plane of symmetry and also lies in the fore and aft central vertical plane of the ship, said plane of symmetry coinciding with said fore and aft vertical plane of the ship when the rudder is aligned fore and aft in the straight ahead position, and a nose portion ahead of the main body and also having a central vertical plane of symmetry coincident with the fore and aft vertical plane of the ship when the rudder is in the straight ahead position, said nose portion being hingedly mounted on the rudder main body so as to be able to turn relatively thereto about a second vertical axis lying in the planes of symmetry of both said main body and said nose portion and forward of said first vertical axis, the nose portion having freedom to turn about said second axis relatively to the main body by an amount up to the same extent as the main body is able to turn about said first axis whereby when the main body of the rudder is put over to an angle said second vertical axis is carried to one side or the other of said fore and aft central plane of the ship but the nose poriton can be kept pointing in fore and aft direction or put over to a different angle.

Arrangements in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Figures 1, 2 and 3 are diagrammatic plan views of three embodiments.

Referring to Figure 1, the nose portion 11 of a rudder 10 is hinged on the rudder main body at 12. The main body is a rigid singleblade hydrofoil section symmetrical about a central vertical plane extending from its leading to its trailing edge, this plane of symmetry being coincident with the foreand-aft central vertical plane of the ship when the rudder is in the straight ahead position. The rudder main body is mounted on a stock to turn about a vertical axis 13 lying in both said planes. The nose portion 11 similarly has a central vertical plane of symmetry coincident with the fore-and-aft central plane of the ship when the rudder is in the straight ahead position, and its hinge axis 12 lies in the planes of symmetry of both the main body and the nose portion ahead of the axis 13.Therefore, as can be seen in the drawing, when the main body turns about the axis 13, the axis 12 is carried to one side or the other of the central vertical plane of the ship. Nevertheless, the nose portion 11 has freedom to turn about the axis 12, relatively to the main body, by an amount up to the same extent as the main body can turn about the axis 13, and so the nose portion may be kept pointing straight ahead as shown or may be at some lesser angle than the main body of the rudder.

The stock centreline 13 may be at any convenient fore and aft position on the chord of the rudder as a whole so as to obtain the best balance of torque when going ahead or astern. A convenient way of visualising the rudder is as a balanced rudder with a hinged nose 11 which latter is linked so as to remain fore and aft or nearly so.

Thus, the overall rudder acquires a considerable camber and this is much more effective at the leading edge 14 than the trailing edge 15 by virtue of the greater curvature of the sections and the greater variations in pressure experienced at the nose of a hydrofoil compared with the tail.

A further advantage is that the rudder can be put over to a greater angle than a conventional streamlined rudder of symmetrical section before the rudder stalls, and thus the peak lift coefficient is appreciably greater.

Furthermore, at normal steering angles, because the nose 11 of the rudder is always pointing more or less straight into the flow emanating from the propeller, the entry is relatively shock-free and there is less likelihood of cavitation and erosion on the nose of the rudder. Again, because the rudder is always pointing fore and aft at its nose, whatever the main body of the rudder may be doing, it is possible to twist the nose of the rudder into the flow, forming a contrapropeller.

While such a twisted nose section is well known and produces a measurable improvement in the propulsive efficiency of the ship, it is not satisfactory with all-moving, symmetrical, balanced rudders. The reason is that, when the rudder is put over to port or starboard, if the sections are twisted there is a tendency when put over in an unfavourable direction to stall one or both of the nose sections. Put over the other way, of course, the rudder is pointing into the flow and is less liable to stall. Nevertheless, it is undesirable that the rudder should stall and twisted nose sections forming a contra-propeller are not commonly used on balanced rudders.

In the arrangement according to the invention, however, this effect is avoided. The nose 11 of the rudder is always pointing directly into the incident flow and it is therefore possible to twist the nose and obtain the advantage of using the nose as a stator or contra-propeller which will improve the propulsion efficiency.

Another advantage is that when going astern the steering torque is much reduced.

In the Lumley rudder the torque is very large going astern and in the conventional balanced rudder it is still large. With the present arrangement, however, because the major "curvature" of the rudder section is near the stock, and anyway near the trailing edge 15, the torque is much less and this is highly advantageous in terms of the size of steering gear, etc.

Alternatively, and referring to Figure 2, both the nose 11 and a trailing edge flap 16 are hinged to the main body 10 of the rudder.

When the main body of the rudder is put over to an angle, the nose 11, as before, is kept pointing in the fore and aft direction, only the main body of the rudder turning to the desired angle. Simultaneously, the trailing edge flap 16 is moved to a greater angle than the rudder 10 by means of a sliding linkage attached to the top of the rudder.

Thus the overall rudder acquires a considerable camber and the advantages described are obtained.

In another arrangement, illustrated in Figure 3, the nose and trailing edge flaps 11, 16 can be arranged to turn to any angle or combination of angles to the main body 10 of the rudder that will produce hydrodynamic characteristics beneficial for a ship's rudder.

WHAT WE CLAIM IS: 1. A rudder on a ship comprising a rigid single-bladed main body with a hydrofoil section which is symmetrical about a central vertical plane extending from its leading to its trailing edge said main body being mounted to turn about a first vertical axis which lies in said plane of symmetry and also lies in the fore and aft central vertical plane of the ship, said plane of symmetry coinciding with said fore and aft vertical plane of the ship when the rudder is aligned fore and aft in the straight ahead position, and a nose portion ahead of the main body and also having a central vertical plane of symmetry coincident with the fore and aft vertical plane of the ship when the rudder is in the straight ahead position, said nose portion being hingedly mounted on the rudder main body so as to be able to turn relatively thereto about a second vertical axis lying in the planes of symmetry of both said main body and said nose portion and forward of said first vertical axis, the nose portion having freedom to turn about said second axis relatively to the main body by an amount up to the same extent as the main body is able to turn about said first axis whereby when the main body of the rudder is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the main body and the nose portion ahead of the axis 13. Therefore, as can be seen in the drawing, when the main body turns about the axis 13, the axis 12 is carried to one side or the other of the central vertical plane of the ship. Nevertheless, the nose portion 11 has freedom to turn about the axis 12, relatively to the main body, by an amount up to the same extent as the main body can turn about the axis 13, and so the nose portion may be kept pointing straight ahead as shown or may be at some lesser angle than the main body of the rudder. The stock centreline 13 may be at any convenient fore and aft position on the chord of the rudder as a whole so as to obtain the best balance of torque when going ahead or astern. A convenient way of visualising the rudder is as a balanced rudder with a hinged nose 11 which latter is linked so as to remain fore and aft or nearly so. Thus, the overall rudder acquires a considerable camber and this is much more effective at the leading edge 14 than the trailing edge 15 by virtue of the greater curvature of the sections and the greater variations in pressure experienced at the nose of a hydrofoil compared with the tail. A further advantage is that the rudder can be put over to a greater angle than a conventional streamlined rudder of symmetrical section before the rudder stalls, and thus the peak lift coefficient is appreciably greater. Furthermore, at normal steering angles, because the nose 11 of the rudder is always pointing more or less straight into the flow emanating from the propeller, the entry is relatively shock-free and there is less likelihood of cavitation and erosion on the nose of the rudder. Again, because the rudder is always pointing fore and aft at its nose, whatever the main body of the rudder may be doing, it is possible to twist the nose of the rudder into the flow, forming a contrapropeller. While such a twisted nose section is well known and produces a measurable improvement in the propulsive efficiency of the ship, it is not satisfactory with all-moving, symmetrical, balanced rudders. The reason is that, when the rudder is put over to port or starboard, if the sections are twisted there is a tendency when put over in an unfavourable direction to stall one or both of the nose sections. Put over the other way, of course, the rudder is pointing into the flow and is less liable to stall. Nevertheless, it is undesirable that the rudder should stall and twisted nose sections forming a contra-propeller are not commonly used on balanced rudders. In the arrangement according to the invention, however, this effect is avoided. The nose 11 of the rudder is always pointing directly into the incident flow and it is therefore possible to twist the nose and obtain the advantage of using the nose as a stator or contra-propeller which will improve the propulsion efficiency. Another advantage is that when going astern the steering torque is much reduced. In the Lumley rudder the torque is very large going astern and in the conventional balanced rudder it is still large. With the present arrangement, however, because the major "curvature" of the rudder section is near the stock, and anyway near the trailing edge 15, the torque is much less and this is highly advantageous in terms of the size of steering gear, etc. Alternatively, and referring to Figure 2, both the nose 11 and a trailing edge flap 16 are hinged to the main body 10 of the rudder. When the main body of the rudder is put over to an angle, the nose 11, as before, is kept pointing in the fore and aft direction, only the main body of the rudder turning to the desired angle. Simultaneously, the trailing edge flap 16 is moved to a greater angle than the rudder 10 by means of a sliding linkage attached to the top of the rudder. Thus the overall rudder acquires a considerable camber and the advantages described are obtained. In another arrangement, illustrated in Figure 3, the nose and trailing edge flaps 11, 16 can be arranged to turn to any angle or combination of angles to the main body 10 of the rudder that will produce hydrodynamic characteristics beneficial for a ship's rudder. WHAT WE CLAIM IS:

1. A rudder on a ship comprising a rigid single-bladed main body with a hydrofoil section which is symmetrical about a central vertical plane extending from its leading to its trailing edge said main body being mounted to turn about a first vertical axis which lies in said plane of symmetry and also lies in the fore and aft central vertical plane of the ship, said plane of symmetry coinciding with said fore and aft vertical plane of the ship when the rudder is aligned fore and aft in the straight ahead position, and a nose portion ahead of the main body and also having a central vertical plane of symmetry coincident with the fore and aft vertical plane of the ship when the rudder is in the straight ahead position, said nose portion being hingedly mounted on the rudder main body so as to be able to turn relatively thereto about a second vertical axis lying in the planes of symmetry of both said main body and said nose portion and forward of said first vertical axis, the nose portion having freedom to turn about said second axis relatively to the main body by an amount up to the same extent as the main body is able to turn about said first axis whereby when the main body of the rudder is

put over to an angle said second vertical axis is carried to one side or the other of said fore and aft central plane of the ship but the nose portion can be kept pointing in the fore and aft direction or put over to a different angle.

2. A rudder according to claim 1, wherein the nose portion is twisted to form a contra-propeller.

3. A rudder according to claim 1 or claim 2, including a trailing edge flap hinged on the main rudder body so that it can be put over to a greater angle than the main body.

4. A rudder on a ship substantially as described with reference to any one of Figures 1 to 3 of the accompanying drawings.