GB2171362A - Improved keel cambering mechanism - Google Patents

Abstract

A mechanism for variably cambering hydrofoil keels for sailing vessels. Previous cambering mechanisms varied the full chordal length of the keel as a unit by curving flexible plates supported near their fore and aft edges and extending unsupported for virtually the full chordal length of the keel. These arrangements resulted in plates having unacceptably low rigidities and cluttered the space within the keel with mechanical components which severely restricted the accommodation available for ballast. The present invention provides a three section keel 7,8,9 wherein rotatable fore and aft sections 7,9 are faired to a fixed center section by flexible plates (14,15) short enough to endow them with rigidities many times as great as those of previous keels while the cambering mechanisms are confined to the spaces within the rotatable sections, leaving the center section free to play its conventional structural and storage roles. Extra stabilising tension is applied to the plates by hydraulic pistons. <IMAGE>

Description

1 GB 2 171 362 A 1

SPECIFICATION

Improved keel cambering mechanism This invention relates to a mechanism suitable for 70 varying the camber of keels for sailing craft. The invention is also applicable to other craft such as aircraft.

Aerofoil data shows that the maximum lift coeffi cient and consequently the total lifting capacity of 75 foils, can be increased by up to fifty percent by in creasing their camber. The data also shows that the angle of attack at which the maximum lift/drag ratio occurs can be reduced from about 5' for cam berless foils, to about 0' for suitably cambered ones, while at least maintaining the lift coefficient corresponding to this optimal angle of attack com pared with camberless foils. Consequently, it will be seen that cambered keels could afford consider able reductions in the yaw angles of beating yachts 85 compared to those of camberless keels. However, since the camber of cambered keels must be re versed on going from one tack to the other, cam ber variation is a prerequisit of cambered keels for yachts and hence the need exists for an efficient 90 camber variation mechanism. Earlier devices for varying the camber of keels were concerned with varying the full chordal length of the keel as a unit.

These designs, incorporating flexible plates sup ported near their fore and aft edges and extending 95 unsupported for virtually the full chordal length of the keel, resulted in plates having unacceptably low rigidities, and cluttered the space within the keel with mechanical components which severely restricted the accomoclation available for ballast. 100 Accordingly, the present invention is designed to overcome the above difficulties, and provides a three sectioned keel in which the cambering and fairing mechanisms are confined to the spaces available within rotatable fore and aft sections, leaving the center section which is rigidly fixed to the boat, intact to play it's conventional storage and structural roles, while the fore and aft sections are faired to the center section by means of flexi ble plates which are only a fraction of the overall 110 length of the keel. Using short plates ensures rigid ities many times as great as those of plates ex tending unsupported over the full chordal length of the keel, with any further required rigidity being in duced by the application of extra stabilising ten- 115 sion to the plates by hydraulic pistons.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a sectional side elevation in the 120 vertical centerplane of the keel; Figure 2 shows an external view of the keel in side elevation; Figure 3 shows an operational schematic view in plan in the horizontal plane 5-6 of figure 1 of the 125 keel.

Referring to the drawings, the multisection keel is shown in side elevation in figure 2 and in fore and aft section through the mid line in figure 1. 8 in figure 1 shows the fixed center section, left in- tact for it's structural and storage functions, with the fairing and cambering mechanisms 3 and 4, restricted to the spaces availanle within the rotatable fore and aft sections 7 and 9, while these sections are faired to the center section with flexible plates as shown at 14 and 15 in figure 2, these plates being only a fraction of the overall length of the keel. Using short plates ensures rigidities many times as great as those of plates extending unsupported over the full length of the keel with any further required rigidity being induced by the application of extra stabilising tension to the plates by hydraulic pistons 65 and 66 in figure 3, in the mathematically positioned rods 63 and 64. Extra stability is insured for the plate on the low pres- sure side in the fully cambered position, by con touring the contiguous surfaces of both the fixed and rotatable sections as shown at 67 and 68 in figure 3, to the required foil section in that area. Pi vot shafts carrying the rotatable sections as shown at 10 and 11 in figure 1 and at 87 in figure 3 are carried on bearings based on the foot of the center section as shown at 12 and 13 in figure 1 at their lower ends and on bearings based in the foot of the hull as shown at 1 and 2 in figure 1, at their upper ends.

A full description of the fairing device including it's method of operation will now be given. Figure 3 shows in planform a rotatable section, desig nated 88, of a multisection variable camber keel and it's junction with the fixed center section, which is designated 60. 71, 72 and 73 represent the positions of the extreme end of the rotatable see tion when it is respectively, centered, rotated to it's extreme anticlockwise position, and rotated to it's extreme clockwise position. When the boat is beat ing on the starbord tack, if 88 represents the front section it will be rotated until it's point is at 72.

This action reduces the camber of the high pres sure side of the keel, 72-77-61-74 and increases the camber of the low pressure side 72-78-62'-75, thus increasing the lift coefficient and hence the lifting capacity of the keel as well as reducing the angle of attack at which the maximum lift/drag ratio oc curs. If the boat is on the port tack the point of 88 will be rotated to 73, thus reversing the camber and optimising the abovementioned parameters for the port tack. The rotatable sections are faired to the center section, so as to enforce prerequired foil sections throughout the range of rotation in the following way. Sheaths, shown at 71-77' and 71 78', are fitted covering each side of the front outer surface of the rotatable section, 88, as shown in figure 3, parallel with the surface and allowing suf ficient space between the sheaths and the rotatable section to accomoclate the front parts of flexible plates, shown at 61 and 62 in figure 3 with said sheaths extending far enough backwards along, and parallel with, the adjacent surface of the front part of the rotatable section, so that when this sec tion is rotated to it's maximum degree to the side of the boat opposite to that on which the particular plate is situated the end of that plate is still well within it's sheath.

These flexible plates are fixed vertically along 2 GB 2 171 362 A 2 their aft ends along positions represented by the lines 16 or 17 in figure 2 and their front ends are shaped to conform to the front vertical foreline of the front section, with their horizontal lengths being arranged so that their front ends come as close as may be required to the vertical foreline of the front section, when the front end of that see tion is rotated to it's maximum extent, to the side on which the particular plate is situated, and when the plate is curved to conform to the prerequired foil section in that position.

Near the front ends of the flexible plates, short processes are fixed at vertical intervals, as shown at 79 and 80 in figure 3, extending inward through slots in the surface of the rotatable section, carry ing bearings near their inner ends as shown at 81 and 82 in figure 3, said slots extending far enough horizontally to allow free rotation of the rotatable section to it's maximum required extent. Other processes corresponding vertically to those previ ously defined, extend forward from the center sec tion as shown at 83 and 84 in figure 3, through other slots in the rotatable section which also ex tend far enough horizontally to allow free rotation of that section to it's maximum required extent.

These processes from the center section also carry bearings near their front ends as shown at 85 and 86 in figure 3, said bearings being connected through pivots to the rods shown at 63 and 64 in figure 3, which rods connect them through pivots to the corresponding bearings in the processes from the flexible plates, shown at 81 and 82. The positioning of the bearings represented by 85 and 86 is of crucial importance to the functioning of the whole device, so their method of location and their function will now be dealt with.

As the rotatable section, 88, is moved so that it's point moves from 72 through 71 to 73, while the plate 61 in conjunction with the sheath 77-72 passes through a prerequired series of faired 105 curves 72-77-61-74 through 71-77'-6l'-74 to 73-77' 61'-74 the locus of the pivot bearing 81, is a curve 81-81'-81' in the horizontal plane, as seen from fig ure 3, which, since the average curvature differ ence between 72-77-61-74 and 81'-6l'-74 is small compared with the length of the flexible plate, will closely approximate the arc of a circle passing through 81, 81' and 81'. The center of this circle can be found by the usual geometric means, and 5O.having found this point, the center for a circle which even more closely fits the established locus can be found by trial and error within a circle of a mm or so radius around it. Actually, for a reason to be elaborated later it is better to have 85-81 equal to 85-81' with 85-81' marginally shorter, so the center for a circle should be found passing through 81 and 81' and passing as close inside 81' as possible. When the center for the pivot bearing is found in this way and the rod 63 of length between the centers of it's pivots equal to the ra dius of the circle, is fitted as shown, the forms 72 77-61-74 through 71-77'-6l'-74 to 73-77'-6l'-74 are infinitely repeatable as the rotatable section is ro tated from side to side during beating operations.

When designing a keel, no great problem is in- volved in impressing any series of forms required for a given operational purpose, on the above series. When the point of the rotatable section is at 73, plate 61 forms part of the low pressure surface and is in contact with the surfaces of both the fixed and the rotatable sections for almose it's entire length, so any prerequired foil form can be enforced in that position by profiling the surface of the center section from 74 to 87 and the surface of the rotatable section from 89 to 73 to the required form. When 61 forms part of the high pressure surface ' that is when the point of 88 is at 72, virtually any prerequired form can be enforced by a combination of the following devices: 80 1). By suitably contouring the part of the surface of the rotatable section which is contiguous with the sheath; 2). By suitably adjusting the distance 72-77 which the sheath is carried aft; 85 3). By suitable location of the fore and aft fixing point 74; 4). By suitable adjustment of the maximum angle of rotation of the rotatable section; 5). By suitable adjustment of the percentage of the chordal distance at which the pivot shaft shown as 87, is located.

When the boat is off the wind, the rotatable seetion would be rotated to the neutral position, 71, where the keel is not lifting and it's required chief attribute is minimum drag. This attribute is determined by the thickness/chord ratio, the slickness of the surface and the foil forms near the entry and exit, but is not significantly altered by small variations in the form 71-77'-6V-74 so the pivot point 81' does not have to be quite as accurately enforced as 81 and 8V.

Any further required stabilising tension for the plates 61 and 62 can be applied through the hydraulic pistons shown at 65 and 66 in the rods 63 and 64 in figure 3, such pistons being controlled from inside the boat through hydraulic lines pasing through the slots in 60 which accomodate the rotation of 88 past 83 and 84. Preferably the hydraulic pistons 65 and 66 are controlled in both compres- sionandtension.

As shown in figure 1, the stabilising assemblies described above are repeated as often as necessary to achieve the surface rigidity required, at suitable intervals from the top of the keel to the bottom.

While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Accordingly, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents.

Claims (12)

1. A hydrofoil shaped multi section variably camberable keel comprising a fixed centre section and cambering and fairing mechanisms restricted to the space available within respective rotatable 3 GB 2 171 362 A 3 forward and/or aft sections, said sections being faired to the said fixed centre section by means of flexible plates which are only a fraction of the overall chordal length of said keel, and said cam- bering and fairing mechanisms controlling the rotational position of their respective rotational sections.

2. A keel according to claim 1 wherein the center section is rigidly fixed to the boat and from the foot of said center section, supports protrude fore and aft, and which carry bearings centered in the fore and aft centerline of the boat and beneath other bearings on the fore and aft centerline carried in the foot of the boat hull, on which bearings, pivot shafts carry said forward and aft sections of the keel, so that these sections can be rotated at will from within the boat.

3. A keel as defined in claim 1 or 2 wherein an edge of each of the said flexible plates is vertically fixed to the sides of the said center section of the keel, another edge of each of the said flexible plates being shaped to conform to the most longitudinally distant vertical line of it's respective rotational section.

4. A keel according to claim 3 wherein the horizontal lengths of said plates of said forward section being so arranged that their forward ends come close to the vertical foreline of the forward section when the forward end of that section is rotated to the maximum degree which might be required, to the side on which the plate in question is situated, and when the plate is curved so that it's front end touches the surface of the front section and it's surface is faired to the contiguous sur- face of the center section.

5. A keel according to claims 3 or 4 wherein the horizontal lengths of said plates of said aft section being so arranged that their aft ends come close to the vertical aftline of the aft section when the aft end of that section is rotated to the maximum de- 105 gree which might be required, to the side on which the plate in question is situated, and when that plate is curved so that it's aft end touches the surface of the aft section and it's surface is faired to the contiguous surface of the center section.

6. A keel as defined in any one of the claims 1 to 5 wherein sheaths are fitted covering each side of the front outer surface of the said forward section and allowing sufficient space between the sheaths and the adjacent surfaces of the said forward section to accomoclate the front parts of said flexible plates of said forward section, and with said sheaths extending far enough backward along and parallel with the surface of the said forward section, so that when the front end of the said forward section is rotated to it's maximum degree to the side opposite to that on which a particular plate is situated, the end of that plate is still within it's respective said sheath.

7. A keel according to any one of claims 1 to 6 wherein sheaths are fitted covering each side of the aft outer surface of the said aft section and allowing sufficient space between the sheaths and the adjacent surfaces of the said aft section to ac- comodate the aft parts of the said flexible plates of the said aft section, with said sheaths extending far enough forward along and parallel with the surfaces of the aft section, so that when the aft end of that section is rotated to it's maximum degree to the side opposite to that on which a particular plate is situated, the aft end of the said plate is still within it's sheath.

8. A keel according to any one of the claims 1 to 7 wherein a first plurality of processes are at- tached at vertical intervals near the free ends of said flexible plates, said processes extending inward through slots in the respective rotatable sections, with the slots in the rotatable sections extending far enough horizontally to allow free rotation of said sections to their maximum required extent and tensioning means connected to the inner ends of said processes.

9. A keel according to claim 8 wherein further processes, equal in number to and situated at the same vertical level as said first plurality of processes, extend respectively forward and backward from the center section, through slots in the respective rotatable forward and aft sections, said slots extending far enough horizontally to allow free rotation of said sections to their maximum required extent and said further processes being connected to said tensioning means.

10. A keel according to claim 9 in which said further processes carry near their outer ends, bear- ings centered on the centers of circles passing through the terminal points of the loci traced out by said inner ends of said first plurality of processes as the respective said sections are rotated, and with the circles concerned passing as close as possible on the center side of the remaining points on the loci with said tensioning means attached to said further processes at the respective said bearings.

11. A keel according to any one of claims 8 to 10 in which said tensioning means incorporate hydraulic pistons or rams of adjustable length.

12. A keel cambering mechanism substantially as described herein with reference to figures 1, 2 and 3 of the accompanying drawings.

Printed in the UK for HMSO, D8818935, W86, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.