WO1996005102A1

WO1996005102A1 - Rudder

Info

Publication number: WO1996005102A1
Application number: PCT/NO1995/000136
Authority: WO
Inventors: Pål G. EIDE
Original assignee: Eide Paal G
Priority date: 1994-08-16
Filing date: 1995-08-14
Publication date: 1996-02-22
Also published as: NO943017L; AU3356495A; NO179606B; NO179606C; NO943017D0

Abstract

A rudder for a watercraft comprising two or more substantially vertical rudder blades (1, 2) positioned one after the other in the longitudinal direction of the craft. The rudder blades are fastened to two substantially horizontal end plates, an upper plate (3) and a lower plate (4). The fastening of the rudder blades to the end plates is made in such a manner that one or more slits (5) are formed between the rudder blades. The design of the rudder blades is based on known foil sections (as, for example, NACA sections) which can be adapted to meet various criteria. The upper end plate may, if necessary, be dimensioned for transmitting the moment from the rudder stock (6) to the rudder blades (1, 2).

Description

Rudder

This invention relates to a rudder for a watercraft. The rudder comprises two or more substantially vertical rudder blades having one or more open slits therebetween. These rudder blades are fastened between two (upper and lower) substantially horizontal end plates.

The rudder is primarily of the type having a rudder stock

10 transmitting rotary motion from the rudder engine or similar apparatus of a craft to the rudder blades via the upper end plate and/or one of the rudder blades. No rudder blades will be rotated relative to the rudder stock. The rudder, is applicable to most types of craft, but Is especially suitable

15 to those types of craft where a rudder of great power (lift) is desirable (for example, for maneuvering, towing, positio¬ ning, and so forth). An effective rudder can in some cases also replace stern thrusters.

20 Effective high-lift rudders have previously been patented; however, most of these consist of movable parts and vul¬ nerable mechanisms in connection with flaps mounted on the rear edge of the rudder. The use of slits in surfaces which provide lift (aerofoils and hydrofoils) is known both in the

25 aircraft Industry and In the sallmaking business (respec¬ tively, canard wings and wing master). German Patent Specification 1,025,291 describes a rudder with some kind of silt, said rudder having a mechanism which opens the silt depending upon the deflection of the rudder for the reason

'° that the foremost rudder blade is hinged at its front edge. Upon Reflection of the rudder the opening of the slit is thus increased because the rear end of the foremost rudder blade is rotated to the side of the front edge of the rear- rudder blade. n the normal position the silt Is completely

'5 closed. What is particularly achieved by the present invention is rudder providing especially high lift without the aid of a complicated and vulnerable mechanism.

A rudder of this type Is generally fitted at the stern a astern of the main propeller of the ship. The maxim deflection of the rudder can be adapted to meet vario criteria. The height of the rudder blades (the distan between the end plates) Is generally the same as t

¹0 propeller diameter of the vessel. The extension of t rudder blades, and thereby that of the slit, in the longit dinal direction of the ship can be adapted to meet vario criteria. The length of the end plates must be sufficient cover the length of the rudder blades and the silts.

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The object- of the present Invention is to provide a rudd which has better lift characteristics than those of ordina one-blade rudders without silts, but which simultaneous reduces movable parts and vulnerable mechanisms to a minim

20 in relation to existing high-lift rudders. Furthermore, t rudder will provide a more pronounced stalling angle th traditional rudders do. Thus, in opposition what occurs wi traditional rudders, the laminar hydrodynamlc flow across t rudder surfaces will remain intact even at large rudd 5 deflections and the lift characteristics will thereby retained. Such conditions will occur during maneuverin tugging, towing and positioning of vessels, where the spe of the vessel Is low but the force of the engine, and there the flow from the propeller, Is strong. The resistance

*> the rudder through water will not be greater than for corresponding marine rudders, however, the rudder th being advantageous In use also for vessels capable of hi speed.

'5 The advantageous hydrodynamlc properties of the rudd comprise primarily high lift/lateral force, for the reas that larger deflections of the rudder can be used without breaking up the flow into turbulence.

The invention is to be further explained with reference to the drawings of a rudder according to the invention, said rudder consisting of two rudder blades and a silt, wherein

Fig. 1 Is a side view of a rudder designed according to the invention;

Fig. 2 shows section A-A of Fig. 1 which in the horizontal plane depicts the rudder blades and the lower end plate;

Fig. 3 shows section B-B of Fig. 1 which Is a horizontal plane of the rudder stock and the upper end plate;

Fig. 4 shows In a horizontal plane the flow conditions and the hydrodynamlc interaction in the silt between the rudder blades at large deflections of the rudder;

Fig. 5 shows the rudder viewed from astern.

The rudder stock (6), transmitting power from the rudder engine to the rudder blades, Is secured at its bottom via the upper end plate (3) of the rudder, said plate having been adequately dimensioned. The rudder Is first and foremost characterized by the two rudder blades (1, 2). These are fastened between the upper end plate (3) and the lower end plate (4), as shown in Fig. 1, so that an open vertical silt (5) is formed between them. The"flow of water entering across the high-pressure side (7) of the rudder will be directed through the slit (5) and will thence and further astern stay close to the rear rudder blade on the low¬ pressure side (8) of the rudder. The form of the rudder blades can be based on known foil sections, as, for example, NACA sections, which can be adapted to meet various criteria. The advantage of this Invention is due to the followi circumstances:

5 (a) Since most of the lift of a foil section occurs the leading edge, the silts (5) will contribute the lift being generated at the optimal position the preceding rudder blade (1). In addition, the Is the effect from having more leading edges, a ι° thus more areas of high lift present In the rudder.

(b) The stalling angle of a rudder is the angle of t deflection at which the flow across the low-pressu side (8) of the rudder surface is broken up (turb

'5 lent flow occurs). This results In a sudden a significant reduction in lift and thereby in rudd power. At such large angles of deflection the fl through the silts (5) will be In the direction of t chord of the rudder, thereby contributing to dire 0 the total flow across the low-pressure side (8) the rudder in the same direction. This entails th the flow Is kept unseparated at the low-pressure si (8) of the rudder blades at greater angles deflection than what will be possible with traditi ns nal one-blade rudders.

(c) At the upper edge and the lower edge of the rudd the pressure difference between the high-pressu side and the low-pressure side will tend to

'» levelled down because of water flowing from the hig pressure to the low-pressure side, across t direction of travel for the vessel. In that ca the effective area of the rudder may be reduced. order to prevent this effect along the rim, t

J5 rudder blades (1, 2) are provided with a common upp end plate and a common lower end plate (3, 4). Seen In its totality, the present rudder design leads to Increased lift and reduced drag. This entails, In other words, that the torque moment determining the capacity of the rudder engine lβ reduced, whereas the inclination moment In the rudder stock is Increased. This means that the demands on steering engine power for maintaining the deflection of the rudder are reduced.

Claims

Patent Claims

1.

A rudder for a watercraft comprising two or more rudd blades positioned one after the other, c h a r a c t e r i z e d I n that the rudder blades (1, are substantially vertically mounted and fastened to an upp end plate (3) and a lower end plate (4), so that one or mo open vertical silts (5) are formed between the rudder blade

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2.

A rudder according to claim 1, c h a r a c t e r i z e d i n that the rudder blades (1, have a shared upper end plate (3) and a shared lower e 1 plate (4) extending across the whole length of the rudder.

3.

A rudder according to claims 1 or 2, c h a r a c t e r i z e d I n that the rudder blades ( 20 2) always occupy the same position in relation to each oth when the rudder Is rotated..

4.

A rudder according to claims 1 or 2, 5 c h a r a c t e r i z e d I n that the rudder blades (1, are mounted so as to be rotatable In relation to each oth about their vertical axes.

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