GB2322336A - Underwater foils in waterborne vessels - Google Patents

Abstract

An underwater foil assembly comprises a vertically movable foil member 5 housed within a casing 14 configured and dimensioned to allow limited movement of the foil member 5 about a hinge line 15 such that hydrodynamic loads upon the foil member automatically increase its angle of attack to the water flow thus reducing the vessel's leeway on either tack. Vertical adjustment of the foil 5 may be achieved by varying its buoyancy. Metering compressed air into the foil interior via a threeway cock 16 and flexible tube 17 causes water to be ejected from a vent 18 in the base of the foil, thus raising the foil. The cock 16 may also be selected to release air from the foil allowing it to sink to any desired level.

Description

IMPROVED OPERATION OF UNDERWATER FOILS IN WATERBORNE VESSELS Leeway reduction, notably in sailing vessels, is normally achieved by hydrodynamic forces acting upon the hulls in addition to a variety of underwater foils which,with the exeption of the rudder, are usually fixed in azimuth with respect to the hull.

That is to say that when underway the foils normally maintain a zero angle of incidence to the hull centreline but provide an angle of attack to the water flow nominally equal to the leeway suffered by the complete vessel. It is this angle of attack of the underwater foil or foils which usually contributes most to leeway reduction.

Daggerboards, which have existed for generations in one form or another, would today often be of aerofoil section and fitted within a casing of similar section constraining movement laterally and in azimuth while allowing any desired vertical movement. This vertical movement often calls for direct operation by crew members via handles atop the boards, or by mechanical or electrical means.

According to the present invention there is provided an underwater foil assembly comprising a vertically movable foil member housed within a casing configured and dimensioned to allow limited movement of the foil member about a hinge line such that hydroqynamic loads upon the foil member automatically increase its angle of attack to the water flow thus reducing the vessel's leeway on either tack. The said hinge line is defined by a line joining top and bottom constraints at the leading and or trailing edges, or points bathe casing between the foil centre of pressure;ìandithe-faol trailing edge, or a combination thereof.

Constraints are of substantially triangular shape,or substantially rectangular with necked down centres allowing azimuthal rotation of the foils about a nominally vertical centreline between the centre of pressure and the trailing edge.

(14) Fig 1 shows a bird's eye view of a boat l:with two casings ánd fig 2 shows such a foil free in azimuth within its casing 14 with constraints 2-attop and-base of the casing, installed in a boat (not shown) sailing to windward on a starboard tack at about 450 off the wind. Water pressure, on account of the resulting leeway (4) causes the foil (5) to rotate clockwise to a position hard against its constraint (2), its trailing edge acting as a fulcrum within the aft end of the casing. The foil's angle of attack is now (xO + yO) resulting in increased "lift" to windward, less overall drag and increased speed made good to windward.

As the boat changes heading (3) through the wind (clockwise) onto the port tack, the foil, under water pressure, is rotated anticlockwise and similarly reduces leeway on the new tack.

Friction is minimised if the lower constraint provides for fulcrum location of the trailing edge while the leading edge is located by the upper constraint.

A specific embodiment of the "frictionless" version of the invention now follows in which: Fig 3 shows a vertical section through a casing 14 with a top constraint 6, a lower constraint 7, typically near or below the water surface and a foil (daggerboard) 5, normally of streamlined section in the "down" position. The aft component of water pressure (drag) upon the hull due to the forward motion of the vessel causes the foil trailing edge 8 to take up a position in contact with the lower restraint 7 (figs 3 & 5). This sets up a couple (fig 3 arrows tO & ll) and in consequence the leading edge 9 of the foil acts as a fulcrum within the upper restraint 6 in which the gap 13 has now open

edssthus allowing water pressure, coupled with an effective hinge line 15 substantially aft of the working (under water) portion of the foil, to rotate the foil decisively as the boat goes about into the port tack. The geometry of this particular embodiment includes a small pendular movement of the foil but this is of no particular consequence. No structural connection exists between the foil or foils and the boat. When dynamic loads are either reduced or absent the foil is fully floating.

Fig 6 shows adjustment of the foils by varying their buoyancy. Metering compressed air into the foil 5 interior via a threeway cock 16 and flexible 18 tubing 17, ejects water from a ventat the foil base. The cock 16 also releases air from the foil to establish any desired change in level, while maintainance of compressed air in the reservior provides necessary crew exercise. Examples shown represent multihull sections.

Although this system is well suited to multihulls and certain monohulls wherein the assembly may be swept forward or aft, the "buoyancy" aspect of vertical control may be replaced by the commonly used blocks and tackle method or hydraulic or other means, and with the foil assembly suitably ballasted at its base may be fitted to monohulled craft where the high aspect ratio of the foil, together with increased pendulum stability, weight saving and variable draft would provide improved operation of monohulls in general.

Claims (6)

CLAIMS 1. An underwater foil assembly for a waterborne vessel comprising a vertically movable foil member housed within a casing configured and dimensioned to allow limited movement of the foil member about a hinge line such that hydrodynamic loads upon the foil member automatically increase its angle of attack to the water flow thus reducing the vessel's leeway on either tack. 2. A foil as in claim 1 whose vertical adjustment is achieved by varying its buoyancy. Metering compressed air into the foil interior via a threeway cock and flexible tubing causes water to be ejected from a vent in the base of the foil, thus raising the foil. The cock may also be selected to release air from the foil allowing it to sink to any desired level. 33. A foil assembly as in claim 1 in which the foil is suspended and ballasted to maintain the stability of a vessel such as a monohull. 4. A foil assembly as in claims 1 and 3 in which variable draft is achieved via mechanical, hydraulic or other means Amendments to the claims have been filed as follows

1. An underwater foil assembly for a waterborne vessel comprising a vertically movable foil member housed within a casing configured and dimensioned to allow limited movement of the foil member about a hinge line such that hydrodynamic loads upon the foil member automatically increase its angle of attack to the water flow thus reducing the vessel's leeway on either tack.

2. A foil as in claim 1 whose vertical adjustment is achieved by varying its buoyancy. Metering compressed air into the foil interior via a threeway cock and flexible tubing causes water to be ejected from a vent in the base of the foil, thus raising the foil. The cock may also be selected to release air from the foil allowing it to sink to any desired level.

3. A foil assembly as in claim 1 in which the foil is suspended and ballasted to maintain the stability of a vessel such as a monohull.

4. A foil assembly as in claims 1 and 3 in which variable draft is achieved via mechanical, hydraulic or other means

5. A foil assembly as in claims 1,2,3 & 4 wherein the effective extended hinge line passes forward and aft of the foil.

6. A foil assembly as in claims 1,3,4 & 5 in which the sideways (pendular) movement to windward of the deep, ballasted, portion increases the righting moment of a vessel.

Amendments to the claims have been filed as follows 1. An underwater foil assembly for a waterborne vessel comprising a vertically movable foil member housed within a casing configured and dimensioned to allow limited movement of the foil member about a hinge line ashereinbefore defined such that hydrodynamic loads upon the foil member-automati-cally increase its angle of attack to th water flow thus reducing the vessel's leeway on either tack.

2,, A foil as in claim 1 whose vertical adjustment is achieved by varying its buoyancy. Metering compressed air into the foil interior via a threeway cock and flexible tubing causes water to be ejected from a vent in the base of th foil, thus raising the foil. The cock may also be selected to release air from the foil allowing it to sink to any desired level.

3. A foil assembly as in claim 1 in which the foil is suspended and ballasted to maintain the stability of a vessel such as a monohull.

4. A foil assembly as in claims 1 and 3 in which variable draft is achieved via mechanical, hydraulic or other means.

5. A foil assembly as in claims 1,2,3 & 4 wherein the effective extended hinge line passes forward and aft of the foil.

6. A foil assembly as in claim 3 in which the sideways (pendular) movement to windward of a ballasted foil increases the righting moment of a vessel.

6. A foil assembly as in claim 3 in which the sideways (pendular) - movement to windward of a ballasted foil increases the righting moment of a vessel.

Amendments to the claims have been filed as follows 1. An underwater foil assembly for a waterborne vessel comprising a vertically movable foil member housed within q casing configured and dimensioned to allow limited movement of the foil member about a hinge line as hereinbefore defined such that hydrodynamic loads upon the foil member automatically increase its angle of attack to the water flow thus reducing the vessel's leeway on either tack.

2. A foil as in claim 1 whose vertical adjustment is achieved by varying its buoyancy by means of metering compressed air into the foil interior via a threeway cock and flexible tubing causing water to be ejected from a vent in the base of the foil and by means of releasing the air from the foil by further selection of the cock thus allowing water to re-enter the foil.

3. A foil assembly as in claim 1 in which the foil is suspended and ballasted to maintain the stability of a vessel such as a monohull.

4. A foil assembly as in claims 1 and 3 in which variable draft is achieved via mechanical, hydraulic or other means.

5. A foil assembly as in claims 1, 2, 3 and 4 wherein the effective extended hinge line passes forward and aft of the foil.