GB2349623A - Balanced articulated sail rig - Google Patents

Abstract

A rig comprises a single approximately triangular sail held between a yard 2 and a boom 3 which is attached and pivoted to the yard towards its forward end, with the vertical angle of the yard controlled by a tension member. The boom 3 is mounted on top of a stub mast 6 near the centre of the boom 3 and can swivel horizontally, but is constrained by at least one sheet 8,10 near the after end of the boom 3 or yard 2. The sail may be radially battened and reefed (see Figs 2and3) by lines pulling the battens 9 to the yard or boom. Leading edge vortices may be promoted by curvature of the yard and boom and shaping of their cross-sections.

Description

BALANCED ARTICULATED SAIL RIG This invention relates to a balanced articulated sail rig for a sailing boat.

A sail rig is the combination of a sail or sails, mast, spars, and rigging which taken together provides the propulsive power for a sailing boat.

Boat sails take many forms but in general provide propulsive force for a boat as a result of either or a combination of : 1. drag, 2. laminar flow over an airfoil shape creating lift, or 3. vortex generation at a leading edge creating lift.

Sails are usually hung from the top or near the top of tall vertical masts, either directly by means of a halyard (a rope by means of which a sail is raised or lowered), or indirectly by being hung from a yard (a spar from which a sail is hung) itself hung from a mast by means of a halyard. The base or foot of a sail may hang free and be controlled by one or more sheets (a sheet being a rope that controls the position of a clew or lower corner of a sail or the end of a spar to which a clew or other corner of a sail is attached), be connected at one end to the mast, or be connected at the ends or along the entire length to a boom (a spar to which the foot of a sail is attached) which itself may hang free and be controlled by one or more sheets or parrels (a rope controlling the position of a sail relative to the mast) or may be more or less firmly connected to the mast at or toward one end and be controlled at the other by a sheet.

Sail shape may be partially constrained or controlled by more or less flexible battens inserted in pockets in the sail.

The most efficient sail form currently known for a given sail area is the so-called"crab claw"rig, which depends largely for its superiority on the production of lift by the generation of trailing vortices at the leading sail edges.

This rig has been demonstrated in wind tunnel tests to be up to ninety percent more efficient at some angles of sailing than the most currently popular rig, the Bermudan, which depends primarily on the production of lift by laminar flow over an airfoil shaped sail.

The crab claw rig has a slender, approximately triangular, axisymmetric sail set between a yard and boom, the yard and boom being both curved and firmly connected at the forward end, the yard being conventionally suspended from a mast by a halyard, the rear of the boom controlled by a sheet, and the yard to boom joint being positioned forward of the mast by a short parrel to some forward part of the boat.

Leading edge vortices over the crab claw sail appear to be promoted by the yard and boom presenting a sharper edge to to the wind, and larger and faster vortices appear to be promoted by convex curved yards and booms.

This rig is not popularly adopted because of several inherent disadvantages relative to other rigs, primarily the difficulty in tacking about when sailing to windward. In the South Seas proa, on which the rig originated, tacking is often achieved by reversing the direction of sailing of the boat and then turning through an angle, so that the prow becomes the stern, and vice versa. This would be impractical for most common hull shapes. To tack efficiently on asymmetrical hulls, the crab claw would have to be lowered, the rig moved to the other side of the mast, and then raised. Such a procedure used to be employed on some lug sail rigs, but required a large crew, and was slow and cumbersome.

Reefing systems (means of reducing sail area to deal with increased wind velocity) appear not to have been developed on crab claw rigs, meaning that their use in areas and at times where there is high or significantly variable wind is questionable. It appears that some reefing effect may be achieved by allowing the boom to move upwards relative to the yard allowing t4p sail to"belly"out, but when winds become higher the sail must be dropped.

An articulated sail rig has been described where an approximation of the crab claw sail form can be deployed between an articulated yard and boom where the yard is pivoted on the top of a stub mast forward of the junction between the yard and boom. This arrangement has several advantages over the conventional crab claw rig, but suffers from the deficiency that in use the centre of effort of the wind acting on the sail moves backwards and forwards relative to the centre of lateral resistance of the hull considerably because of the angle of attack of the wind requiring the angle between the plane of the rig and the heading angle of the hull to be varied. This movement of the centre of effort adversely affects the balance of the boat where the moments are large. The forward position of the supporting pivot on top of the stub mast also leads to high stresses where the rig is relatively large. Both of these deficiencies limit the use of the rig to relatively small craft, for which it is otherwise particularly suited because of the forward position of the mast leaving the volume of the boat free, or to multiple sets on large craft, where complexity of use of multiple occurrences would detract from the advantages of the rig.

According to the present invention there is provided a balanced articulated sail rig comprising a sail suspended between a straight or curved yard and a straight or curved boom. At a point approximately half way along the boom the boom is attached to the top of a stub mast with the motion of the boom constrained to the horizontal plane by means of a pivot or the stub mast itself being capable of rotating. The yard and boom are joined and pivoted at the forward end of the boom and a point towards the forward end of the yard, the yard projecting forward from the junction with the boom, the yard to boom junction being so constructed that the yard can only pivot freely in the vertical plane above the boom. The vertical angle between the yard and boom is controlled by a variable length tension member between the forward end of the yard some distance beyond the boom pivot and a point on either the boom or the stub mast. The position of the after end of the boom, yard, or both are controlled by a sheet or sheets leading from the after end of either the yard or boom or both to a control point.

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 in diagrammatic side view and not to scale a general arrangement of the rig, with reefing lines omitted for the sake of clarity; Figure 2 shows in diagrammatic side view and not to scale an illustration of the position of the battens and reefing lines on the sail; and Figure 3 shows in diagrammatic section and not to scale an illustration of the arrangement of yard, boom, sail, battens and reefing lines before and after reefing.

Referring to the drawing the rig comprises a sail I set between a yard 2 and a boom 3. The yard and boom are joined by a fixed pivot 4 which allows the yard to move about the pivot in a vertical plane above the boom. The boom is fixed to the top of an upper stub mast 6. The upper stub mast 6 is set in a lower stub mast 7 in such a way that the upper stub mast and the attached boom are free to rotate in the horizontal plane.

The vertical angle of the yard, and thus the height and angle to which the sail is raised, is controlled by a halyard running in a pair of multiple pulley blocks 5 to give sufficient mechanical advantage, the halyard then being led backwards to a control point.

The horizontal angle of the yard, boom, and sail are constrained by a sheet 8 acting against the action of the wind. Control may be assisted by a further sheet 10 to the end of the yard, which can also assist in controlling any tendency of the sail to twist.

In sailing, the horizontal angle of the plane of the sail, yard, boom may be at any angle to the heading angle of the hull.

To tack about, the boat would merely be headed on the new direction by means of the rudder; the rig is self-tacking, and the sail will come about naturally.

Similarly, in gybing, the boat would be controlled by the rudder, but in this case the sheet must be brought in and then released as the boat goes about to prevent violent motion of the sail and spars, particularly if the wind be strong.

The sail is dropped by bringing in the sheet and releasing the halyard, when first the boom is brought parallel to the heading angle of the hull, and then the yard would come to lie on the top of the boom. If necessary constraining lines analagous to"lazy jacks"could be provided to keep the sail close to the yard and boom, but these would need hauling in as the yard was lowered, unlike lazy jacks which are lines either side of the sail fixed between the mast and boom in a conventional rig.

The reefing arrangement is shown in figures 2 and 3. Two radial battens 9 are provided on alternate sides of the sail. Sets of reefing lines 12 and 13 operate on alternate sides of the sail, one set to each batten. Two lines per set are shown for the purpose of illustration; more or less may be required depending on the size of the sail. A reefing line leads from the batten to the yard (alternately the boom) then to the boom (alternately the yard), and then down the boom (alternately the yard) to the top of the stub mast (in the case of the lines down the yard via the boom pivot 4) and thence to a control position.

Pulling in the reefing lines causes the battens to be drawn nearer to the yard and boom, folding the sail between them in a sideways Z shape. The sail is then in the reefed position. Only one set of battens and reefing lines is illustrated for clarity, but if required multiple sets may be provided to give multiple fixed reefing settings, though a single set can be adjusted to give intermediate settings at the cost of a less than perfect sail fold.

To unreef, the reefing lines are relaxed, and a combination of the weight of the sail and boom, and the pull on the sheet, will open up to the unreefed position.

On large sails, additional sheets 11 to the ends of the battens may be added to assist in the control of the horizontal angle of the sail and to counteract any tendency of the sail to twist.

Claims (5)

1. CLAIMS 1 A balanced articulated sail rig comprising a sail suspended between a straight or curved yard and a straight or curved boom. At a point approximately half way along the boom the boom is attached to the top of a stub mast with the motion of the boom constrained to the horizontal plane by means of a pivot or the stub mast itself being capable of rotating. The yard and boom are joined and pivoted at the forward end of the boom and a point towards the forward end of the yard, the yard projecting forward from the junction with the boom, the yard to boom junction being so constructed that the yard can only pivot freely in the vertical plane above the boom. The vertical angle between the yard and boom is controlled by a variable length tension member between the forward end of the yard some distance beyond the boom pivot and a point on either the boom or the stub mast. The position of the after end of the boom, yard, or both are controlled by a sheet or sheets leading from the after end of either the yard or boom or both to a control point.
2. 2 An articulated sail rig as claimed in Claim 1 where the sail is radially battened and may be reefed by tension members pulling the battens towards the yard or boom such tension members being led down the boom or yard via the boom pivot to the top of the mast and thence to a control point.
3. 3 An articulated sail rig as claimed in any preceding claim where additional control over the sail position is obtained by a sheet taken from the after end of the yard.
4. 4 An articulated sail rig as claimed in Claim 2 or Claim 3 where additional control over the sail position is obtained by sheets taken from the after ends of the battens.
5. 5 An articulated sail rig as claimed in any preceding claim where the yard and boom are themselves so shaped by curvature in length and/or fixed or varying shape of cross-section as to promote the generation of leading edge vortices when deployed in a stream of wind.

   5 An articulated sail rig as claimed in any preceding claim where the yard and boom are themselves so shaped by curvature in length and/or fixed or varying shape of cross-section as to promote the generation of leading edge vortices when deployed in a stream of wind.

   Amendments to the claims have been filed as follows CLAIMS 1 A balanced articulated sail rig comprising a sail suspended between a straight or curved yard and a straight or curved boom joined and pivoted at the forward end of the boom and a point towards the forward end of the yard with the yard to boom junction being so constructed that the yard can only pivot freely in the vertical plane above the boom, the whole being supported at a point approximately half way along the boom by the boom being attached to the top of a stub mast with the motion of the boom constrained to the horizontal plane by means of either a pivot or the stub mast itself being capable of rotating, the angle of rotation of the boom being controlled by a sheet leading from the after end of the boom to a control point, and the vertical angle between the yard and boom being controlled by a variable length tension member between the forward end of the yard some distance beyond the yard to boom pivot and a point on either the boom or the stub mast.

   2 An articulated sail rig as claimed in Claim 1 where the sail is radially battened and may be reefed by tension members pulling the battens towards the yard or boom such tension members being led down the boom or yard via the boom pivot to the top of the mast and thence to a control point.

   3 An articulated sail rig as claimed in any preceding claim where additional control over the sail position is obtained by a sheet taken from the after end of the yard.

   4 An articulated sail rig as claimed in Claim 2 or Claim 3 where additional control over the sail position is obtained by sheets taken from the after ends of the battens.