DE8810058U1 - Device for directional stabilization of a fast watercraft - Google Patents

Description

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Device for directional stabilization of a fast Watercraft

The invention relates to a device for directional stabilization of a fast watercraft according to the preamble of claim 1. The invention relates in particular to a fin device of a sailboard, but it is also applicable to other devices for directional stabilization such as a daggerboard held in a daggerboard case and for other fast watercraft.

In order to achieve the necessary directional stability, fast watercraft generally have a fin at the stern, which is held in a fin holder, usually in a fin box, into the interior of which the fin engages with a foot section. Underneath the underwater hull, turbulent flow conditions often prevail when traveling fast, which can cause a strong increase in pressure on the fin, so that it can lose its ability to stabilize the direction. This can lead to the watercraft breaking out sideways (spin out).

In order to prevent the watercraft from breaking away due to turbulent flow conditions at the fin, it has been proposed, for example, in DE-OS 34 25 233 to arrange horizontal guide surfaces on the tiller, which divert turbulence backwards in the direction of flow in order to limit its detrimental influence. In OE-OS 32 15 235 it has been proposed for the same purpose to provide the fin with a profile that changes towards the free end.

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cross-section with a transition from a slim, low-resistance, symmetrical profile to a relatively thick symmetrical profile. From DE-OS 34 42 920 a fin is also known which has a flow vortex separation element in the area where the fin is connected to the fin holder and/or the vehicle underbody.

All known measures have in common that they cannot reliably prevent a fast watercraft from breaking out sideways (spinning out) due to the fin's ability to stabilize direction being impaired by flow conditions.

The present invention is based on the object of further developing a device for directional stabilization of the type in question so that its effectiveness is considerably improved.

This object is achieved according to the invention by the features specified in the characterizing part of claim 1. Advantageous further developments of the invention are characterized in the subclaims.

The device for directional stabilization according to the invention contains a hydrodynamically favorable edge recess in the area of the exit of the directional stabilization component, preferably a fin, from the underwater hull, which is formed into the outer surface surrounding the exiting fin. This rounding of the transition from the underwater hull to the fin completely prevents the formation of turbulence in this area, which would otherwise result in a strong increase in resistance.

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lift and cause the watercraft to eventually break out (spin out).

The inventive design of the sub -Y wascerschiff emerging fin enclosing outer surface

; is based on the knowledge that the underwater ship

i'j and the fin emerging from it as two vertically

e The two wings are to be considered as two wings facing each other, the meeting of which causes interference drag. This interference drag appears as a turbulence wedge. The formation of this turbulence wedge is due to the fact that the fin, which acts as a bluff body, generates a strong pressure increase, which causes the boundary flow layer to separate from the fin and is known as the so-called diffuso effect. The increase in drag can be so great that it causes the dreaded sideways breakout of the watercraft.

The hydrodynamically favourable edge recess surrounding the emerging fin ensures that the same pressure conditions prevail in the transition area of the fin to the over-water vessel as in the undisturbed fin profile. This means that the extremely disadvantageous turbulence wedge or the diffusion effect is avoided. The pressure reduction caused by the edge recess provided according to the invention largely corresponds to the pressure increase caused without this edge recess, so that this pressure increase that occurs with conventional fin devices is not affected by the inventive fin device.

p according device is eliminated> This is a main

cause of the watercraft breaking out sideways eliminated, so that the finnenvöir according to the invention,.,-

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fulfils its task of directional stabilisation considerably more effectively.

The edge recess formed in the outer surface surrounding the exiting fin should extend continuously around the entire circumference of the fin and be directly connected to the fin. Particularly effective pressure relief is achieved when the edge recess merges tangentially into the flat outer surface of the surrounding area at its beginning and end, as seen in the direction of flow.

The line of maximum depth should form an asymmetrical, flat trough shape when viewed in the longitudinal direction of the edge depression, which reaches its deepest point before reaching half the length. As a result, the edge depression initially runs steeply inwards when viewed in the direction of flow, before tapering off more flatly after reaching the deepest point. Apart from the preferably tangential start, the line of maximum depth of the edge depression should essentially correspond to one of the symmetrical halves of a laminar profile, as is advantageously provided for the fin of the fin device according to the invention.

The exact geometric shape of the edge depression can be determined by the known pressure ratios on the profile of the fin and the associated underwater reef.

For practical purposes, a Finnish canopy is provided as an internal shelter, which is inserted into the underwater shelter in such a way that its outer surface is without any

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The edge recess is flush with the corresponding outer surface of the underwater vessel. The edge recess is conveniently set into the outer surface of the fin box, for which purpose the latter can have a widened cross-sectional section in sections perpendicular to its longitudinal axis. The pressure-relieving edge recess can be formed particularly easily and precisely on the fin box.

Further details of the invention emerge from the following description of a preferred embodiment and from the drawing. In the drawing:

Fig. 1 is a side view of a fin device according to the invention;

Fig. 2 is a section through the fin of Fig. 1 along line 2-2;

Fig. 3 is a section along the line 3-3 in Fig. 1 and

Fig. 4-6 Cross sections through the fin chest according to Fig. 1 along the lines 4-4, 5-5 and 6-6 in Fig. 1.

Fig. 1 shows a fin 1, which sits with its foot 2 (Fig. 5) in a fin chain 3, in which it is held by means of two narrowly formed, rail-shaped projections that engage in correspondingly aligned grooves 5 of the fin chain 3. As Figures 2 and 3 show, the fin has

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a laminar profile whose velocity and pressure distribution are precisely defined.

The fin box 3 is embedded in the underwater hull of a watercraft (not shown) in such a way that its outer surface 6 is flush with the surrounding outer surface of the underwater hull. The outer surface surrounding the fin 1 emerging from the fin box 3

6 of the fin box 3 is a generally indicated in the figures with

7, the maximum profile depth of which is shown schematically in Fig. 1 by the dashed line 8. From this line it can be seen that the edge recess 7 runs tangentially into the remaining outer surface 6 at the beginning and at the end and, viewed in the direction of flow, reaches its deepest point, which is indicated by the arrow 9, before reaching half the axial length. Following the deepest point 9, the edge recess 7 runs out relatively flat.

The fin box 3 has, as shown in Figures 4-6, a widened cross-section 10, into which the edge recess 7 is formed. Viewed in the direction of flow in front of and behind the fin 1, the edge recess 7 has a flat, symmetrical trough shape, as shown in Figures 4 and 6, while in the area of the fin on both sides it is approximately V-shaped (Fig. 5).

From Fig. 3 it can be seen that the width of the edge recess 7 follows a course that corresponds approximately to the laminar profile of the fin 1, but the edge recess runs out to a considerable width.

Claims (1)

'* ^: ' patent attorney cwioogarvrschflwtenkirchen DR ₁ -INGJURGENFlOSDORFF telefS^2Tt3666 BJROPEANPArENTATTORNEY TELEGRAM FUOPATENT TELECOPIER:+8821-71944 G III - 24 h NORTH SAILS WINDSURFING GmbH Penzberg N 842 Expectations 1. Device for directional stabilization of a fast watercraft, in particular a fin device of a sailboard, with a fin holder in which a fin is held, which engages with a foot section in a cavity of the fin holder, characterized in that the outer surface (ti) surrounding the fin (1) emerging from the fin holder (3) has a hydrodynamically favorably shaped edge recess (7). 2. Device according to claim 1, characterized in that the edge recess (7) extends continuously around the entire associated circumference of the fin (1). -Z- 3. Device according to claim 1 or 2, characterized in that the edge recess (7) directly adjoins the corresponding circumferential line of the fin (1). 4. Device according to one of claims 1 to 3, characterized in that the edge recess (7) is connected approximately tangentially to the flat outer surface (6) at its beginning and end, viewed in the flow direction. 5. Device according to one of claims 1 to 4, characterized in that the line (8) of the maximum depth of the edge recess (7) seen in the direction of flow forms an asymmetrical, flat trough shape which takes up its deepest point (9) before reaching half its length. 6. Device according to one of claims 1 to 5, characterized in that the line (8) of the maximum depth of the edge recess (7) as seen in the flow direction essentially corresponds to one of the symmetrical halves of a laminar profile. 7. Device according to one of claims 1 to 6, characterized in that the geometric shape of the edge recess (7) is determined by the pressure conditions on the profile of the fin (1) and the associated underwater vessel. 8. Device according to one of claims 2 to 7, characterized in that a fin box (3) is provided as fin support. • t · · · I -3- I &thgr;. Device according to claim &bgr;, characterized in that the groove (7) is formed in the outer surface (6) of the fin box (3), which otherwise runs flush with the underside of the underwater hull. 10. Device according to one of claims 1 to 9, characterized in that the fin box (3) has a widened cross-sectional section (10) in planes perpendicular to its longitudinal axis for receiving the edge recess. 11. Device according to claim 10, characterized in that the widened cross-sectional section (10) has a V-shape. 12. Device according to claim 10 or 11, characterized in that the widened cross-sectional section (10) extends over the entire length of the fin box (3). &Idigr;3. Device according to one of claims 1 to 12, characterized in that the fin (1) has a laminar profile.