GB2188300A - Rudder system for marine vessels - Google Patents

Abstract

In a ship's steering and propulsion system, flanking rudders 10 are provided for steering the ship when going astern, which rudders have aftwards extensions 13. The rudders 10 are forward of a nozzle or duct 12 and the extension 13 on one rudder or the other closes up to the adjacent side of the nozzle nose 21 when the rudders are put over to obviate undesirable leakage around the nozzle nose at that side. The extensions 13 may be fixed or they may be articulated to turn to a lesser angle than the main blades of the rudders. Also provided is a linkage for turning the trailing edge flaps on the rudders to a lesser angle, or the leading edge flaps to a greater angle, than the angle of turn of the main rudder. <IMAGE>

Description

SPECIFICATION Ships steering and propulsion systems This invention relates to ships' steering and propulsion systems.

Multiple rudder systems, especially in association with ring propulsion ducts, have been demonstrated to be highly effective and U.K. PatentSpecification No. 2 079 231 describes such a system developed particularly for high transverse thrust at low forward speed but at quite high propeller loadings. This system may be used on its own as described in the above mentioned patent specification or it may be used in conjunction with a bow lateral thrust unit.

The system is also very suitable for use in highly loaded propulsion systems in tugs, fishing vessels, etc. where transverse th rust may be required not only going ahead but also going astern. When used in this way, however, the absence of rudders in the jet efflux, which is directed forward, much reduces the steering efficiency and sidewaysthrust of the system. It is common practice to fit forward or 'flanking' rudders when astern requirements are impor- tant and there is no invention in providing such flanking rudders.

However, when the flanking rudders 10 (Figure 1) are put over there is a considerable leak between the propulsion duct 12 and the nose of one flanking rudder (the nose being the tail if the vessel is proceeding ahead but the nose if the vessel is proceeding astern). This leak which is shown bythe arrow 11 in Figure 1, is particularly obtrusive because of the socalled Coanda effect produced bythewaterflowexit- ingthe nozzle at what is normally its forward end and which is heavily curved. This heavy curvature attachestheflowand pulls it round sothe effluxfrom the nozzle is at a considerable angle to the centre line. The momentum change produced by this diver sioncounteractstheliftproduced bytheflanking rudders and much detracts from the efficiency ofthe device.

The present invention seeks to provide a means of avoiding this leakage and commences from an approach to trailing rudders embodied in the abovementioned Patent No.2079231, the so-called 'Butterfly Bow Shutter Rudder System'.

According to the invention, a flanking rudder is provided with an aftward extension; in the case of nozzle or duct propulsion, the aftwards extension is arranged so that the extension on one flanking rudder or the other comes substantially into contact with the adjacent side portion of the nose of the nozzle or duct when the flanking rudders are put overforsteer- ing purposes, in order to minimize or substantially avoid the undesirable leakage referred to above; if no nozzle orduct is present, the aftward extension of each flanking rudder is nevertheless arranged to materially improve the efficiency of steering ofthe vessel when going astern.

In one preferred form, the aftward extension of the flanking rudder is in the form of a trailing edgeflap or blade that is arranged,when theflanking rudder is put overto a steering angle, to turn to a smaller steering angle than the main blade of the flanking rudder.

In another aspect, there is provided means for put- ting over a rudder extension flap to a differentangie from the main blade ofthe rudder, comprising an upstanding pivot offset transversely from the rudder stock, a til ler fixed to the flap and extending laterally therefrom, and an arm mounted on the pivot and pivotally connected at its free end to the free end of the tiller. If the flap is to be put overt a lesserangle than the main blade then the pivot and the tiller arm will be on the same side ofthe fore and aft center line ofthe rudder; but the arrangement can also be employed in cases where the flap is to be put over to a greater angle than the main blade, in which eventthe pivot and the tiller will be on opposite sides ofthe fore and aft center line.

In a further aspect, there may be flaps hinged atthe forward edges of the flanking rudders, with control means forcausing each forward flapto turn to a greater angle than the respective rudder when the rudder is put over.

Arrangements according to the invention will now be described in more detail by way of example and with reference to the accompanying drawings, in which Figure 1 shows a prior art propulsion duct arrangement with flanking rudders, Figure2 shows in elevation an arrangement according to the invention, Figure 3 is a plan view of the arrangement of Figure 2, Figure 4shows the prior art arrangement of Figure 1 with a skeg, Figure 5is a plan of another arrangement accord- ing to the invention in which each flanking rudder has a trailing edge flap, Figure 6shows a mechanism for operating thetrailing flap in the arrangement of Figure 5, Figure 7shows a mechanism for putting overthe trailing flap in the opposite direction, Figure 8 is a plan view of a further arrangement according to the invention in which each flanking rudder has a leading edge flap, and Figure 9 illustrates the operation ofthe arrangement of Figure 8.

Figure2 isanelevationalviewoftheflanking rudders 10 with an aftwards extension 13 on the aftside of each rudder, namely the tail when going ahead or the nose when going astern. This extension is so curved and arranged that when the rudder is overto a suitable large angle, which may be 60 or as high as 75 the extension comes in contact with or very close to the leading edge or nose 21 of the adja centside portion oftheduct 12 and sealsitoff, thereby preventing the escape ofwaterthrough the gap and avoiding the above mentioned disadvantageous Coanda effect.For this purpose the extension 13 constitutes an aftward protrusion from the conventional straight vertical trailing edge 22 ofthe rudder 10, which protrusion is itself bounded by a trail- ing edge 23 that has a curved profile and at its lower end intersects the straight trailing edge 22 of the main bladeatthe bottom corner24 ofthe rudder 10 while at its upper end it intersects the trailing edge of the main blade at a position 25 some distance below the top of the rudder 1 the whole trailing edge prot rusion 13 being vertically symmetrical aboutthe horizontal plane containing the axis ofthe duct 12.

The extension on the other rudder 10 does not, of course, at this time effect any sealing but nevertheless significantly increases the area of rudder exposed to the flow and therefore helps the transverse diversion of the water flow exiting the forward end of the nozzle when going astern. The arrangement when in this situation is shown in plan view in Figure 3, and it can be seen thattheflow past one rudder 10 is substantially totally diverted and the other largely diverted. The arrangementthus offers the possibility of a considerable increase in the efficacy of forward flanking rudders 10when going astern, increasing the transverse force on the stern of the vessel.A further advantage of the extension is that it reduces the over-balance ofthe forward flanking rudders 10 and improves their steering geartorque characteristics.

Ideally, there should be no obstruction of there suIting cross-flow a nd if there is no such obstruction then the result is that a transverse force is produced which is wholly advantageous and improves the manoeuvrability ofthe vessel. However, many vessels not specially designed for this capability have a deadwood or skeg which can act as an obstruction to the transverse flow from one of the two rudders, in particularthe rudder which is the more efficient of the two, namely the one which effects the sealing ofthe flow exiting from the nozzle atone side. This effect is shown in Figure 4, which is the same as Figure 1 but with the water flow beyond the rudder indicated and the position of a typical skeg 14 shown.

If the flow from a rudder 10 impinges upon the skeg 14then redirection into a fore and aftdirection takes place, as indicated by the arrows 26, and it can be seen thatthis opposes the steering motion desirably being produced.

It is thus beneficial in such circumstances, to producea design offlanicing rudderwhich notonlyseals the leak and prevents a loss of thrust due to the Coanda effect but also produces a downwash angle exiting the rudder in a forward direction which does not impinge upon the skeg. Figure 5 shows such an arrangement.Use is made of a flanking rudder, again with an extension which is capable of sealing the exit (when going astern) from the nozzle and which also embodies an adaption of the known principle ofthe Lumley Rudder, first produced in the mid-1 800's and fitted atthattime to a considerable number of ships. Inthepasttwentyyearsorsothis type of rudder has been used extensively by designers in Britain and Germany underthe name ofthe 'Lumley Rudder' orthe 'Becker Rudder', the principle of this rudder being that when the main blade turns a linkage causes a trailing edgefiapto turn still further.

In the arrangement of Figure 5, however, the inverse of the Lumley Rudder is used, namely when the main blade 10turnsthetrailing blade 15turnsto a smallerangle. It can be seenthatthe slave blade 15 will seal the forward exit (when going astern) at the adjacent side of the duct or nozzle as before, thus preventing the Coanda effect leak, but additionally the main blade 10 can turn through a considerable angle of the order of 75.800 as shown at 16. In the case ofthe blade 10 which does not come up against the duct, the slave flap aftwards extension 15 effects a shock-free unstalled entry to the flanking rudder and again,the main blade 10causeswaterto exitata very high downwash angle ofthe order to 75-80".

This rudder system considerably increases the efficiency ofthe forward flanking rudders when going astern even if there is no skeg present, but is is particularly beneficial to efficiency in the presence of a skeg because it is possible to design the rudderto avoid impingement on the skeg ofthe water exiting the nozzle in a forward direction. Thus, this embodiment ofthe invention is a desirable modification of the first embodiment and a considerable advance upon normal forward flanking rudder practice. For extreme manoeuvrability it offers particularadvantages not available from anyothersystem.

This being so, it is possibleto use this rudder configuration in the absence of a duct, as it offers the advantage of improved astern steering on any vessel such as a river push-tow tug which relies upon both ahead and astern steering for manoeuvring in difficult situations. In other words, the slave flap blade arrangement may be used as an alternative to an all one-piece flanking rudder in the presence of a nozzle or it may similarly be used as a flanking rudder without a nozzle or duct.

In Figure 6, a simple mechanism for achieving the desired angle ofthe closure flap or slave flap is shown. Avertical pivot 17 is situated on the bottom shell to one side of the rudder stock 18 in a transverse plane at right angles to the centre line of the vessel.

This pivot is fixed and on it is mounted a bell-crank or arm 19 suitably bushed etc., which in turn is pivotally connected at its after end by a similar eye and bush to atiller20 on the same side ofthe centre line ofthe rudder 10 as the pivot 17 and attached to the slave or closure flap 15. Thetillermay, in a particularform, be at right angles to the slave or closure flap but this is not an essential feature and any convenient angle may be chosen between the axis ofthe flap and that of thetillerto suitthe particuiar geometrical con- figuration of the vessel .

The offset of the pivot 17 transversely from the rudder stock 18 is less than the length of the tiller 20 attached to the slave or closure flap 15. When the rudder is put over to a particular angle, as at 27, the bell-crank or arm 19 moves the slave flap 15 to an angle from the centreline axis 28 of the flanking rudder 10 itself. Because the offset transversely from the rudder stock is less than the length of the tiller, the angle through which the slave or closure flap 15 moves is less than the angle through which the rudder 10 moves and the desirable result shown in Figure5 is thereby achieved.

This simpleform of actuating mechanism is not, however, restricted to the arrangement of Figure 6 but it can be used more widely, that is to say with conventional Lumley Rudders where it is desired that the angle of the slave flap shall be greaterwith respect to the centreline than that of the rudder itself.

In this case, the pivot 17 is not on the same side ofthe centreline of the rudder as the tiller of the slaveflap but is on the opposite side. This is shown in Figure 7, where it can be seen that the pivot 17 is to the port side ofthe stock 18 and the tiller 20 on the slave flap 15 in this particularexample isto starboard. Thus, when the rudder 10 is put overto a given angle, as at 29,the slaveflap 15 is movedto a greaterangle and the ratio between these two angles may be chosen at will by a suitabie proportioning between the offset of the pivot and the length of the tiller attached to the slave flap.

Referring now to FigureS, an arrangement is shown in which the flanking rudders 10 are extended at their aftward edges to fit into the entry ofthe duct or nozzle 12 and thus fulfil the sealing function nec essary to prevent escape of water by the so-cal led Coanda effect on the side of the nozzle which one rudder approaches, as with Figure 2. Attheforward edge of each rudder 10 there is a flap 30 hinged to the rudder which moves to a greater angle than the rudder 10 when the rudder is put over, the operating mechanism being ofthe kind shown in Figure 7.

As can be seen, when the rudders 10 are put over to approximately 400 the flaps 30 move to a much larger angle. In the case ofthe starboard rudder in Figure 1,this angle is 900 to the centreline of the ship and in the case of the port rudder, it is 1000. Thus it can be seen that when the vessel is going astern, with the rudders 31 aft ofthe nozzle 12 remaining fore and aft, the two forward flanking rudders 10 are put over by their own steering gear to 40 from fore and aft and theflaps 30 which are attheforward edges of the flanking rudders (trailing when going astern) are then moved automatically by the hull pivots and linkages to 90" or more to the centreline of the ship.Water exiting the nozzle on the port side is diverted by the port flanking rudderto a large angle which is ofthe order of 900 from its previous direc tion of motion. On the starboard side the water cannot escape around the curved forward edge 21 of the nozzle and is forced bythe starboard flanking rudder 10 to move across the ship and then by the flaps 30 to exit at a large angletothe centreline clear of anymore and aftskeg 14 on the centreline ofthe ship that may be obstructing transverse flow.

Figure 9 shows a composite diagram ofthe oper- ation of this system and it can be seen that when the rudders 10 are fore and aft, as they would beforfor ward motion of the vessel, they are substantiallyfore and aft not only in terms of the flanking rudders themselves but also in terms of the articulated flaps 30 on the forward edges of the rudders. The posi tionsofthehull pivots and the linkage arrangements can be adjusted so that the leading edge flaps 30 have a desirable toe out angie to suit the inflowto the nozzle or duct 12 when the vessel is moving ahead.

This is also shown in Figure 9 where a suitable toe out of 3" is illustrated and obtained by the linkage shown.

The angles given in this description are typical but not exclusive. The flanking rudders may be arranged to goto anysuitableangle of helm, notonlythe4o0 shown, and thefull helm angleoftheflaps30tothe fore and aft axis of each flanking rudder may be 60 as shown or may be more or less astheconfiguration ofthe particular vessel demands. Similarly, the toe out angle of the articulated flap on the leading edge of each rudder may be 3 as shown but may be any other angle that suits the particular entryflow conditions of a particular duct and vessel.

The forward rudder system described may be used with a dedicated steering gear separate from that of the after rudders. In that case, the after rudders are operated by a separate dedicated steering gear; but the invention includes the use by suitable linkages of a single steering gear for both fore and aft rudder systems.

In the claims appended hereto, words such as 'forward', 'aftward', 'leading', 'trailing', 'nose' etc. are intended to be given the meaning that they have when the vessel is going ahead.

Claims (12)

1. A ship's forward flanking rudder provided with an aftwards extension arranged to enhance the efficiency of the steering ofthe vessel when going astern.

2. Aflanking rudderaccording to Claim 1, wherein the aftwards extension is a trailing edge flap which is arranged to turn to a smaller steering angle than the main blade of the flanking rudder.

3. Aship's propulsion system comprising a nozzle or duct and incorporating flanking rudders according to Claim 1 or Claim 2forward ofthe duct, wherein the aftwards extension on each flanking rudder is arranged so that the extension on oneflanking rudder or the other comes substantially into contact with the adjacent side portion of the nose of the nozzle or duct when the flanking rudders are put overforsteering purposes, in order to minimize or substantially avoid the undesirable leakage that would otherwise occur around the nose of the duct at that side.

4. A system according to Claim 3 when appended to Claim 1, wherein the aftwards extension on each flanking rudder consists of a fixed aftward protrusion of the trailing edge which protrusion has a convexly curved trailing edge profile and is vertically sym metrical about the horizontal plane containing the axis ofthe duct.

5. Rudder control means for putting over a rudder extension flap to a different angle from the main blade of the rudder, comprising an upstanding pivot offset transversely from the rudder stock, a tiller fixed to the flap and extending laterally therefrom, and an arm mounted on the pivot and pivotallycon- nected at its free end to the free end ofthetiller.

6. Control means according to Claim 5, wherein the pivot and the tiller arm are on the same side of the fore and aft centre line of the rudder.

7. Control means according to Claim 5, wherein the pivot and the tiller arm are on opposite sides of the fore and aft centre line of the rudder.

8. A ship's propulsion system according to Claim 3 when appended to Claim 2, and wherein the trailing edge flaps on the flanking rudders are controlled by control means according to Claim 6.

9. Aships'sflanking rudder for steering when going astern, having a leading edge flap that is arranged to turn to a greater steering angle than the main blade oftheflanking rudder.

10. A rudder according to Claim 9, wherein the leading edge flap is controlled by control means according to Claim 7.

11. A ship's propulsion system according to any of Claims 3,4 or8, having flanking rudders in accordance with Claim 9 or Claim 10.

12. A ship's propulsion and/or steering system, substantially as described with reference to Figures 2 and 3, or Figures, or Figure 6, or Figure 7, or Figures 8 and 9, ofthe accompanying drawings.