GB2072599A - Rudders - Google Patents

Abstract

The invention relates to a rudder 10 for watercraft and floating equipment, in which the rudder constructed as a normal profile rudder is provided with attachments 20, 21 on its trailing edge and by the said attachments is partially converted into a hollow flanking rudder. The rudder blade is also provided with laterally projecting, plate- like rudder disks 30 and 31. <IMAGE>

Description

SPECIFICATION Rudder for watercraft and floating equipment The invention relates to a rudder for watercraft and floating equipment Rudders are as a rule displacement members attached at one or more points to the stern having an airfoil-like profile and a straight axis and which, with or without the action of the propeller or screw produce the rudder force necessary for controlling the ship if adjusted to a rudder angle. Rudders are passive control members which energetically tap the main drive of the ship or the passage flow energy.

Watercraft and floating equipment comprise station ary and moving displacement members and struc tures, off-shore platforms and drilling rigs. Towed and submerged vessels such as pontoons, barges, floating docks and submersible craft also fall into this category.

It is known that approximately 2/3 of the rudder action is produced on the suction side and approxi mately 1/3 on the pressure side. In aeronautics slats have been successfully used for preventing suction side cavitation. In the shipping field driven and disconnectable rotors have proved suitable and they are located either in the leading edge of the rudder or in bends of multipart rudders. As is known the pressure side effect of the rudder can be improved by fins operated on the trailing edge of the rudder by mechanical coupling from the outside or forced conrol from the inside. Unlike with the previously described attachments on a rudder, improvements can be obtained relatively easily on the pressure side of the rudder by using fixed structures.These include outboard fins fixed to the upper and/or lower edge of the rudder, chocks on the trailing edge of the rudder and combinations of both these attachments.

In addition, hollow flanking profiles are known which produce an improved rudder action. The adaptation of the rudder shapes to the helical flow of the propeller for energy recovery purposes leads to twisted rudder members.

However, all these known constructions do not improve the rudder action and the twisting of the rudder member takes place counter to the oblique incident flow from the helical flow starting at the leading edge of the rudder and extending over the front rudder area or the entire depth of the rudder.

Rudders are subject to the oblique action of the helical flow of the preceding propeller and specifical ly in the case of right-handed propellers in the upper port area and the lower starboard area. These helix 'angles are approximately 20 . Thus, with a resulting zero transverse force the rudder supplies a consider able induced resistance which must be applied by the driving unit of the ship. The propeller also causes the rudder to oscillate or vibrate, because the pressures on the rudder are periodically built up and removed in the case of oblique instant flow. The oblique instant flow in the upper rudder area leads to serious damage due to cavitation erosion in the case of fast ships.Due to the oblique instant flow with semi-balance rudders the lower starboard side of the balance surface is more effective than the facing port side, so that the torques to be applied by the steering gear are generally highly asymmetrical and lead to unnecessary overdimensioning of the steering gear.

Chocks on the trailing edge of the rudder have almost exclusively a pressure side effect, the rudder force gradient being scarcely increased and the point of application of the rudder transverse force migrates rearwards, so that the rudder torques rise steeply. The rudder resistance when travelling straight ahead is increased approximately 5 times compared with the resistance of a normal rudder.

Such parasitic effects are also encountered with combinations of rudders having chocks and outboard fins. These characteristics are not encountered with hollow flanking rudders They produce approximately 30% higher rudder forces over the entire rudder angle range and in the case of the conventional rudder construction with symmetrical profiles and straight axis require a 30% more powerful steering gear.

Gaps are formed between the components fixed to the ship and the rotary parts of a rudder. The components fixed to the ship are in the case of semi-balance rudders the rudder post and a fixed rudder fin over the rudder and in the case of spade rudders not located freely in the flow the fixed rudder fin over the rudder in which is frequently also positioned the rudder post journal bearing. Whereas in the case of midships rudder angles and small rudder angles these gaps are substantially closed, they open even with normal rudder angles during the constant course corrections of the ship.Due to a local pressure balance between the pressure side and the suction side of the rudder this leads to four parasitic effects: a) the effectiveness of the rudder is considerably reduced, b) the gap flows produce powerful vibrations, c) the rudder produces an increased drag resistance, d) the gap flows lead to increased erosion damage on the rudder due to cavitation.

This rudder cavitation is produced by the locally very high speeds and the very low pressures and soon leads to serious damage to the rudder in the case of rudders subject to propeller action in the fast ships. In the case of semi-balance rudders this damage occurs in the vicinity of the gap close to the lower pintles on the rudder post, in the upper part of the balance surface and in the rear part of the rudder in the gap flow wake and on the rudder base. In the case of spade rudders effects a) to c) dominate, because this rudder type is rarely used on fast ships with heavy-duty propellers.

It is known that the flow round the upper edge of the rudder can be eliminated in the case of small rudder angles by the aforementioned rudder fins fixed to the ship or outboard fins can be provided for reducing the flow round the lower edge of the rudder. This has a positive influence on the aspect ratio of the rudder as an airfoil. Outboard fins on the upper and lower edge of the spade rudder are provided on the SCHILLING rudder and KAUFER rudder. In addition, tests have been carried out to eliminate the parasitic effects relative to gaps by fitting rubberflaps to the leading edge which hang over the gaps when the ship is moving. In addition, irregularities on the rudder blade surface, such as sharp edges, welds, doubling plates, etc. increase the risk of local cavitation, whereas rubber cavitation is mainly caused by the propeller.

However, it has been found that cavitation problems and in particular the cavitation effects referred to hereinbefore, cannot be solved by changing the drive propeller construction and in fact constructional modifications can only be carried out on the rudder. Serious erosion damage due to rudder cavitation is particularly encountered with fast container ships and propeller-operated rudders, as well as with twin-screw ferries with double rudders. No technical solution for eliminating these parasitic effects is known.

The problem of the present invention is to provide a rudder adapted to the helical flow of the propeller and which is based on a conventional rudder, e.g. a spade or semi-balance rudder. It must simultaneously be possible to convert such a rudder from the outset or subsequently into the novel rudder, without it being necessary to strengthen the constructional connections and steering gear.

Another problem is to be able to so construct semi-balance and spade rudders under fixed rudder fins for watercraft and floating equipment that gap flows between components fixed to the ship and movable rudder parts and the associated parasitic effects are avoided.

According to the invention this problem is solved by a rudder for watercraft and floating equipment, wherein the rudder constructed as a normal profile rudder is provided with attachments on its trailing edge and by these can partly be converted into a hollow flanking rudder.

The attachments comprise rudder parts in the form of profile members arranged at approximately half the rudder height and on opposite sides of the rudder trailing edge, so that the rudder and each rudder part forms a curved rudder axis and of the said axes one ends on tthe left-hand side and the other on the right-hand side.

According to another embodiment of the invention the rudder is constructed in such a way that for preventing parasitic effects due to the compensating flow in the gap opening when operating the rudder laterally projecting, plate-iike rudder disks with a suitable profile are provided between the movable rudder parts and the fixed rudder parts above and/or below the gap on either side of the rudder blade or on either side of the fixed rudder post.

According to the method of the invention it is possible to convert from the outset or subsequently a normal displacement rudder into a twisted rudder with bent or curved axis by one-sided, asymmetrical attachments in the rear rudder part. The advantages obtained are on the one hand the low constructional expenditure for the improved rudder made necessary if the ship has to carry out new manoeuvres through operating in different areas or if ships are subsequently lengthened or are completely rebuilt except for the stern. On the other hand the hydrodynamic advantages can be attributed to the reduced oblique incident flow angle due to the modified rudder axis, the positive characteristics of the hollow flanking profile with respect to the rudder forces and the adaptation of the heights of the asymnmetrical attachments to the helical flow of the propeller.

When travelling straight ahead the drag resistance and vibrations are reduced, whilst there is a reduced susceptibility to cavitation phenomena, influencing of the "neutral rudder angle", and when manoeuvring there is an increased rudder effectiveness when turning and supporting the moving ship and when stationary using the slip stream, whilst the rudder torques can be influenced in connection with the port-starboard symmetry characteristics.

Other advantages obtainable as a result of the present rudder are a considerable improvement to the hydrodynamic characteristics of rudders which wholly or partly have gaps either from the outset or subsequently by simple, robust constructions, which are readily interchangeable. By eliminating gap flows vibrations and the rudder resistance are reduced and the rudder effectiveness considerably improved. Local cavitation phenomena are reduced or even eliminated. Thus, for example, if the energy removal as a result of gap flow and eddy formation in the gap between the balance surface and the rudder post is prevented with a semi-balance rudder, there is a simultaneous considerable improvement in the rudder effectiveness due to the pressure compensation prevented between the pressure and suction sides.As a result smaller rudder angles can be used, which further reduces the rudder resistance. Thus, the advantages obtained can be summarized as the characteristics of an energy-saving, low-vibration and a less cavitation susceptible rudder with improved rudder characteristics in the range of normal to average rudder angles. Existing rudders can be converted into the improved rudder in a simple, rapid and inexpensive manner.

Further advantageous developments of the invention can be gathered from the subclaims.

The invention is described in greater detail hereinafter relative to a non-limitative embodiment of a one-piece spade rudder and the attached drawings, wherein show: Figure 1 the upper part of a twisted rudder with an attachment in the rear part of the rudder in pian view along the section line ll-ll of Figure 2.

Figure 2 the asymmetrical attachments on the rudder and the step between the two attachments located approximately halfway up the rudder in a view from the rear in the case of a right-handed propeller.

Figures 3, 3a, 3b embodiments of the step between the two attachments in an oblique view along line l-l of Figure 1.

Figure 4 the flow-kinematic conditions around a ship for a stationary turning circle.

Figure 5the flow-kinematic conditions around a ship and specifically the rudder set to a rudder angle and the incident flow direction.

Figure 6 a rudder with attachments on its trailing edge and outboard fins arranged on the upper and lower edges of the rudder in a three-dimensional view.

Figure 7the embodiment of Figure 6 in side view.

Figure 8 part of the stern with a drive propeller and Fa semi-balance rudder with rudder disks arranged on either side of the gap over the balance surface and a further rudder disk arranged on the upper edge of ,the rudder in side view.

Figure 9 a spade rudder in an arrangement below a fixed rudder fin with a rudder disk in side view.

Figure 70 a horizontal section through the rudder blade with a rudder disk in two different embodi ments.

In the embodiment of Figures 1 and 2 10 is a one-piece spade rudder, whose trailing edge is 11.

The control and drive mechanisms for the rudder 10 are not shown.

Attachments or rudder parts 20, 21 are arranged on the trailing edge 11 of the rudder 10 at approxi mately half the rudder height and on facing sides of said trailing edge 11. The two attachments 20,21 are shaped asymmetrically to one another on the trailing edge 11 of rudder 10 and are fixed to rudder 10 as separate components. Detachable fastening is also possible and this is always advantageous if attach ments 20, 21 with a different shape are used. The asymmetric arrangement of attachments 20,21 is shown in Figure 2. The embodiment of Figure 2 applies to a right-handed propeller. As is also apparent from Figure 2 each attachment 20 or 21 is arranged on the right or left-hand side, so that curved axes are obtained. The axis for the upper attachment 20 is indicated at 20a in Figure 1.As shown in Figure 1 this axis 20a ends at the right hand side, whilst the axis through the rudder 10 and the lower attachment 21 is indicated at 21a in Figure 1 and ends at the left-hand side. The two axes 20a, 21a can be bent or curved. The transition of the asymmetrical attachments 20, 21 can be inclined (Figure 3a) or horizontal (Figure 3b) or in the form of a flat centre plate 25. (Figure 3). The step between the two attachments 20,21 is indicated at 24 in Figure 2.

It is also possible in per se known and not shown manner to provide the rudder 10 with a rotor which influences the suction side or a fin which influences the pressure side.

The attachments 20,21 on the trailing edge 11 of rudder 10 can also be bounded by end disks 30, 31 arranged on the upper and lower edge of the rudder (Figures 6 and 7).

Figure 4 shows the flow-kinematic conditions around the ship with a stationary turning circle, particularly drift angle ssh at the stern. This is the angle between the midships direction and the flow direction by which, in approximate manner, the rudder angle bR is reduced. Figure 5 shows the rudder set to rudder angle 5R and the incident flow direction. The attachment provided on the rudder trailing edge 11 at one side acts over a wide area K, so that the known improvements of the airfoil characteristics are also made possible with the represented rudder. Axis 20a assumes a curved configuration. If the rudder is oppositely positioned the identical attachment arranged in the other rudder part acts in the same way.Due to the curved axis of the overall profile area K has a much more favourable action with regards to the maximum rudder force with minimum resistance than the per se known chocks.

In Figures 4 and 5 the references have the following meanings: S = centre of gravity P = centre (Figure 4) M = centre of rotation a =, distance between S and P = = drift angle at centre of gravity Ph = drift angle at stern = = rudder angle P = propeller (Figure 5) K = rudder area with flap function In the case of the semi-balance rudder 110 constructed in per se known manner and shown in Figure 8 120 is the rudder blade, pivoted to the rudder post 125. The upper and lower rudder bearings are 111, 112 respectively. 115 is a drive propeller or screw.

A gap 121 is formed between the balance surface 120a of the rudder blade 120 and rudder post 125. As can be seen in Figure 10 rudder disks 130, 130a are provided in the vicinity of gap 121 being fixed to either side of the movable rudder blade 120 or are flanged in disk form and project laterally. The crescent-shaped projecting lengths of rudder disks 130, 130a in the direction towards the rear area of rudder blade 120 pass into the side plating thereof.

Above rudder disks 130, 1 30a fitted to both sides of rudder blade 120, rudder disks are also provided in the vicinity of gap 121 of rudder post 125, only one of which is shown in Figure 8 and is designated by reference numeral 131. Rudder disk 131 and the other rudder disk which is not shown in the drawing and is located on the other side of rudder post 120 are fixed on either side of the latter in the vicinity of gap 121 or are flanged in disk-like manner and preferably have the same flow profile as the two underlying rudder disks 130, 130a on rudder blade 120. However, a different form of said disks is possible and is indicated at 130b in dotted line manner in Figure 10.This form and construction of the rudder disks is always used if the gap 121 is to be closed, even with larger rudder angles. However the converse procedure can also be adopted in that rudder disks 130, 130a have the form of rudder disks 131, whilst the latter are then constructed like disks 130, 130a, cf. Figure 10.

Due to this arrangement of rudder disks 130, 130a, 131 in the vicinity of gap 121, quite apart from reducing the opening of said gap, a pressure compensation is prevented between the two rudder sides in the vicinity of the maximum pressure difference area, thereby avoiding transverse flow and eddy action in the vicinity of gap 121,so that rudder effectiveness is increased, vibrations, resistance and cavitation susceptibility are reduced.

It is also possible to arrange the rudder disks only on rudder blade 120 or on rudder post 125 or on both rudder parts on either side of gap 121.

In the case of spade rudder 200 shown in Figure 9 220 is the rudder blade which is positioned below a fixed rudder fin 220b. A gap 222 is formed between fin 220b and blade 220.

Rudder disks are arranged below gap 222 on either side of rudder blade 220 and in Figure 9 a single rudder disks 232 is shown. This rudder disks 232 has the same shape configuration as rudder disks 130, 130a, 131. It is also possible to arrange rudder disks above gap 222 on either side of rudder fin 220b, said disks being parallel to disks 232. Of the disks on fixed fin 220b only one disk 233 is visible. Rudder disks 233 are also constructed in the same way as rudder disks 130, 130a and 131,232 and have a corresponding flow profile. The arrangement of rudder disks 233 on fixed rudder fin 220b is particularly advantageous if the gap 222 is to be closed against undesired transverse flows with larger rudder angles.

Even if the aforementioned parasitic effects occur to a reduced extent at gap 222 of the spade rudder 200 shown in Figure 9, by the arrangement of rudder disks 232 and/or 233 a transverse flow in gap 222 is eliminated.

Thus, even in the case of the semi-balance rudder 110 it is advantageous if the upper gap 122 between rudder blade 120 and the fixed fin 1 20b can be closed by means of a rudder disk. As shown in Figure 8 rudder disks 132 are provided here on either side of rudder blade 120 below gap 122 and are constructed in the same way as disks 130, 130a and 131,232 and project on either side. Of the two rudder disks on rudder blade 120 only one disk 132 is shown.

All the rudder disks 130,130a or 131,132 or 232, 233 are either fixed to the rudder blade 120 or 220 or to the fixed rudder fin- 120b or 220b. However, a detachable fixing is also possible, thereby permitting an effortless interchange of damaged or faulty rudder disks. It is also advantageous if disks 130, 130a or 131, 132 or 232,233 are extended beyond the associated rudder blade edge or rudder post edge, as shown in Figures 8 and 9. The projecting portion of the rudder disks can be seen in Figure 10.

Claims (14)

1. A rudder for watercraft and floating equipment, wherein the rudder constructed as a normal profile rudder is provided with attachments on its trailing edge and by these can partly be converted into a hollow flanking rudder.

2. A rudder according to claim 1, wherein the attachments comprise rudder parts in the form of profile members arranged at approximately half the rudder height and on opposite sides of the rudder trailing edge, so that the rudder and each rudder part forms a curved rudder axis and of the said axes one ends on the left-hand side and the other on the right-hand side.

3. A rudder according to claims 1 and 2, wherein the attachments on the trailing edge of the rudder are limited by outboard fins fitted to the top and bottom of the rudder.

4. A rudder according to claims 1 to 3, wherein the transition of the asymmetrical rudder parts passes in an inclined or curved or horizontal manner through a flat centre plate.

5. A rudder according to claims 1 to 4, wherein the rudder is provided with a rotor influencing the suction side or a fin influencing the pressure side, both constructed in per se known manner.

6. A rudder according to claims 1 to 5, wherein the rudder and attachments are constructed in one piece.

7. A rudder according to claims 1 to 5, wherein the attachments are detachably fixed to the trailing edge of the rudder.

8. A rudder according to claims 1 to 7, wherein for preventing parasitic effects due to the compensating flow in the gap opening when operating the rudder laterally projecting, plate-like rudder disks with a suitable profile are provided between the movable rudder parts and the fixed rudder parts above and/or below the gap on either side of the rudder blade or on either side of the fixed rudder post.

9. A rudder according to claims 1 to 8, wherein in the case of the semi-balance rudder arranged under a fixed rudder fin the rudder disks are arranged on one/and/or two sides of the gap between the rudder blade and the rudder fin and/or in the vicinity of the gap between the balance surface and the rudder post.

10. A rudder according to one of the claims 1 to 9, wherein in the case of the spade rudder arranged below a fixed rudder fin the rudder disks are arranged on either side of the gap on the rudder fin and/or on the rudder blade.

11. A rudder according to one of the claims 1 to 10, wherein the rudder disks have a widened profile on their leading edges for closing the gap, even in the case of larger rudder angles.

12. A rudder according to claims 1 to 11, wherein the rudder disks are detachably fixed to the rudder blades and rudder fins or to the rudder post.

13. A rudder for watercraft and floating equipment substantially as herein described with reference to the accompanying drawings.

14. A water vessel fitted with a rudder according to any one of the preceding claims.