WO2007104086A1

WO2007104086A1 - Movable ballast system for sailing vessels

Info

Publication number: WO2007104086A1
Application number: PCT/AU2007/000283
Authority: WO
Inventors: Nicolaas Laurisse Sieling
Original assignee: Nicolaas Laurisse Sieling
Priority date: 2006-03-16
Filing date: 2007-03-08
Publication date: 2007-09-20

Abstract

A system for providing vessels such as racing yachts with movable ballast is disclosed. The system envisages a ballasting weight [3, 3'] arranged to be attached to an arm [2, 2'] that is mounted on a shaft [1] . The shaft is mounted in the hull [H] of the vessel with the longitudinal axis [X, X'] of the shaft in a vertical or near vertical position when the hull is upright. The arm projects to the side of the shaft so that the centre of gravity of the weight is offset from the axis [X, X'}. Where the vessel has a keel [7] that depends downwardly from the centreline of the hull, the shaft passes through the keel and is mounted so as to be capable of rotating about the axis [X, X'} to either side of the fore-and-aft direction of motion of the vessel. The weight may be rigidly attached to the arm or free to rotate about a rotational axis [30] that is substantially parallel to the axis [X, X']. in which case the centre of gravity of the weight is advantageously located on or close to the axis [30]. The weight may be so shaped and mounted as to be able to rotate to a position in which drag due to the weight as the vessel moves through the water is reduced. The arm and the weight may together have the shape of a foil having a longitudinally extending axis of symmetry. The shaft is advantageously rotatable about the axis of rotation [X, X'] through a complete circle but in any case through an angle in excess of 90° to either side of the fore-and-aft direction of motion of the vessel.

Description

MOVABLE BALLAST SYSTEM FOR SAILING VESSELS

This invention relates to movable ballast for sailing vessels, particularly yachts.

Traditionally, monohull sailing yachts have relied on a combination of hull shape and ballast located in the bottom of the hull or at the bottom of the keel to resist the heeling moment caused by the forces of the wind acting on the sails. In recent times however, yachts have been provided with systems for moving the ballast. If weight is shifted to the windward side of the vessel, a greater righting moment to counteract the wind forces on the sail can be achieved. This allows more sail to be carried for a given amount of ballast.

One common way of shifting weight is to shift the crew to windward. In this method the crew commonly sit on the windward rail of the hull. Another common method is to pump water into a tank located on the windward side. This is known as water ballast. A recently introduced method is to provide a keel that can be swung to windward about a longitudinal axis. This is known as the canting keel system.

A disadvantage of sitting on the rail and water ballast is that there is a limit to how far the weight can be shifted to either side. The righting moment is correspondingly limited. Furthermore the righting moment diminishes as the boat leans beyond a given angle and is, relatively, very small when the boat is close to being knocked down.

There are also disadvantages to canting keel systems. Such a system is mechanically hard to achieve. In larger boats the canting is commonly carried out by hydraulic cylinders operated by a hydraulic pump driven by an internal combustion engine. A primary function of the keel is to prevent the boat from slipping to leeward. When canted to a large angle, the keel is no longer able to perform this function efficiently. It may therefore be necessary to employ a second keel, daggerboard or forward rudder to prevent the leeward drift. This increases wetted area and drag. Furthermore, some canting keel systems have recently failed causing, or contributing to, incidents that have put the lives of the crews in danger. STATEMENTS OF INVENTION

According to the invention, there is provided a vessel comprising a hull arranged to be provided with movable ballast, the ballast comprising a ballasting member arranged to be attached to a mounting member mountable in the hull in such manner as to be rotatable about an axis of rotation that is upright in a direction athwartships of the hull when the hull is upright in the same direction, means being provided for attaching the ballasting member to the mounting member in a position in which the centre of gravity of the ballasting member is offset from the axis of rotation.

When the mounting member rotates, the ballasting member will thus rotate with it. The term "athwartships" is intended to convey a direction that is substantially perpendicular to the direction of the fore-and-aft centre line of the hull. In many, if not most, cases of a vessel provided with movable ballast according to the invention, the rotational axis will be theoretically vertical in both the athwartships direction and also the fore-and-aft direction when the hull is floating upright in the water. This will have the effect, at least in theory, that the ballasting member will remain in a horizontal plane as it rotates with the mounting member and there will be no resistance to this rotation arising from the weight of the ballasting member. However, as further explained herein, in certain circumstances the axis of rotation may be canted from the vertical.

Advantageously, and most usually, the mounting member comprises a shaft arranged to rotate about its longitudinal axis and disposed so that it is vertical or near vertical when the hull is in the upright position.

In one aspect of the invention the hull has a keel through which the mounting member is arranged to pass.

In one aspect of the invention, the means for attaching the ballasting member to the mounting member comprises an intermediate member that projects transversely from the mounting member and spaces the ballasting member from the mounting member. In one aspect of the invention, the intermediate member is substantially perpendicular to the axis of rotation. Advantageously, the intermediate member has an external shape that reduces the drag caused by the intermediate member as the vessel moves through the water.

In one aspect of the invention, the ballasting member is rotatably mountable on the intermediate member, advantageously in such manner as to be capable of rotating about a rotational axis that is substantially parallel to the axis of rotation of the mounting member.

In one aspect of the invention the ballasting member is free to rotate with respect to the intermediate member about the rotational axis.

In one aspect of the invention the ballasting member has a centre of gravity that is located on, or close to, the rotational axis.

In one aspect of the invention the ballasting member is so shaped and mounted as to be able to rotate about the rotational axis to a position in which drag due to the ballasting member as the vessel moves through the water is reduced.

In one aspect of the invention the mounting member is rotatable about the axis of rotation through an angle of at least 90°, and advantageously well in excess of 90°, to either side of the fore-and-aft direction of motion of the vessel. This capability enables the ballasting member to be shifted from one side of the vessel to the other between positions in which the centre of gravity of the ballasting member is located at equal and opposite maximum distances from the centreline of the vessel and advantageously well forward of those positions.

Advantageously the ballasting member and the intermediate are shaped to reduce the drag due to each as the vessel moves through the water. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further discussed with reference to the examples shown in the attached drawings in which:

Figure 1 is a view from the right hand (starboard) side of the hull of a sailing boat fitted with a ballasting member mounted below the hull;

Figure 2 a plan view (in larger scale) on arrow A in Figure 2; Figure 3 is a view from aft of the vessel shown in Figure 3, in a typical attitude when it is under sail;

Figure 4 is a view of part of Figure 1 but in larger scale, of a mechanism for mounting and rotating the ballasting member;

Figure 5 is a plan view on arrow B in Figure 4, of the mechanism for mounting and rotating for the ballasting member; Figure 6 is a sectional view of part of Figure 4 but in still larger scale, of part of the mechanism for mounting and rotating the ballasting member;

Figure 7 is a sectional side view of an arrangement for mounting the ballasting member;

Figures 8a- 8d are plan views of four positions to which the ballasting member can be rotated;

Figures 9-13 are views, similar to Figure 4, of some alternative ballasting arrangements according to the invention;

Figures 14a- 14c are views from the side, top and front respectively of part of the arrangement shown in Figure 9; Figures 15a-l 5c are views from the side, top and front respectively of the arrangement shown in Figure 10.

It will be clear that most of the arrangements shown in the drawings are substantially schematic.

Referring first to Figures l-8d, a lead weight 3 is rotatably attached to the outer end of an arm 2, the inner end of which is rigidly attached to the lower end of a shaft 1 to form what is conveniently called a ballast assembly 100 mounted on a sailing vessel. The weight 3, arm 2 and shaft 1 are examples of what are referred to generally in this specification and the claims as a ballasting member, an intermediate member and a mounting member respectively. Each of these members could take any other suitable form. For example, the ballasting member may comprise a simple solid body of suitable shape and material such as the lead weight 3 shown or could comprise solid or particulate material housed in a casing. Furthermore, the ballasting member and the intermediate member may be separately formed and rotatably joined together, as in this example, or could be formed as a single unit, as in the example shown in Figures 10 and 15a-15c, as a one-piece casting or moulding. The primary function of the ballasting member is the same as that of any ballast in a sailing vessel, namely to counteract the force of the wind on the sails of the vessel and help keep the vessel as upright as possible. This function is well understood and does not need further explanation.

It will be understood that, in any case in which the intermediate member is massive, whether or not it is formed as a unit with the weight, the intermediate member could also have a significant ballasting function.

In the present example, the sailing vessel is a racing yacht provided with a hull H fitted with a fin keel 7 but the invention is not limited either to such a vessel or such a keel. The keel 7 is mounted on the bottom of the hull H. As is usual, the hull and the keel are symmetrical about a plane disposed along the fore-and-aft centre line C of the vessel. Of course, in the absence of significant ballast mounted to one side or the other of the centre line C, the centre of gravity of the vessel would conventionally lie in this plane. The shaft 1 passes through the keel 7 and is rotatably mounted as described in detail below so that its longitudinal axis X, which is also its axis of rotation, lies in the abovementioned plane of symmetry and is substantially upright (i.e. theoretically vertical) when the hull is upright. The arm 2 projects transversely from the shaft 1. In the present case the arm is perpendicular to the shaft, though this is not essential. The function of the arm is to support the ballast in a position in which there is a space between the centre of gravity of the weight 3 and the axis X (and thus the centre of gravity of the vessel). In the present case this space is approximately equal to the length of the arm 2. By rotating the shaft about its axis of rotation X, the weight can be moved to a position, as discussed in detail below, in which it has the effect of applying a righting moment to the hull. The weight 3 and the arm 2 are shaped to minimise wetted area and drag due to their form and presence in the water. To this end, in this example, the arm 2 is symmetrical about a line of symmetry S extending along its length. The arm is relatively thin and flat and may be suitably shaped to act as a hydrofoil.

In the assembly 100, the weight 3 comprises a body of circular cross sectional shape similar to a torpedo with a vertical tail fin 28. The weight is mounted on the outer end of the arm 2 in such manner that the weight is capable of rotating freely on the arm 2 about a rotational axis 30 that is parallel to the axis of rotation X of the shaft 1 fitted to assembly 100. To accommodate the rotation of the weight 3, the arm 2 is arranged so that it projects horizontally from the shaft 1 when the shaft is vertical.

The rotational axis 30 passes through the centre of gravity of the weight 3. Moreover, the weight 3 is shaped so that the forces applied by the water to the weight 3 as the vessel moves in a given direction (usually but not always, forward) cause the weight to rotate about the axis 30 to a position in which the drag due to the weight is minimised.

In the present example the weight 3 is mounted below the arm. However, in a modification, the weight 3 could be mounted above the arm. This could be the only substantial difference between these two examples.

The manner of mounting the weight 3 on the arm 2 is shown in Figure 7. A stub shaft 32 projects downwardly from the lower face of the arm 2. The stub shaft is journalled in a bearing 34 housed in a cylindrical passage 36 bored through the body of the weight. The bearing may be a corrosion resistant roller bearing or a bush of wear resistant plastics material. The weight 2 is retained on the shaft by a nut 38 that is screwed and covered by a protective cap 23. In the present example, the weight 3 is free to rotate about the stub shaft 32 and thus relative to the arm 2.

In Figure 3 the weight, arm and shaft are shown relative to the vessel hull H and its mast M. The sails are not shown. As is well known, the forces of the wind in the sails, with the wind coming from the right hand (starboard) side, will make the vessel heel to the left (port). Also shown are the theoretical centre of flotation 4 and the surface of the water 5. When the vessel is upright the waterline of the vessel is, by definition, level with the surface 5. In the position shown in Figures 2, 3, 5 and 8c the weight 3 has been rotated to the windward (starboard) side of the hull so that the line of symmetry S is positioned at 90° to the centre line C of the hull. Figures 2 and 3 show that, in this position of the ballast assembly, the arm 2 is able to position the weight 3 well outside the point of maximum beam of the hull. The weight thus creates a much larger righting moment around the theoretical centre of flotation 4 than can be achieved with crew on the rail or water ballast within the hull.

In windless conditions, when the vessel is carrying no sails and the weight 3 has been rotated so that it is displaced from the centre line C, the action of the weight 3 will cause the vessel to heel to starboard. In the present case, when the line S is at 90° to the line C, so that the weight 3 is as far as it can go to one side, the angle of heel is about 10° although the invention is not limited to this angle.

The provision of the assembly 100 has various advantages. The arm 2 can be rotated to any angle that best suits the point on which the vessel is sailing. Whatever this angle is, the weight will pivot about the stub shaft 32 to take up a position, usually fore-and-aft, in which it presents the least resistance to the water as the boat moves through the water. For example, when the vessel is sailing dead before the wind, it is well known that the wind force on the sail tends to force the nose of the vessel down into the water and thus slow the vessel down. Rotating the arm 2 so that the weight 3 moves aft can counteract this tendency. In the most extreme case, as shown in Figure 8d, the weight 3 will be directly behind the keel 7. On the contrary, when the vessel is sailing hard on the wind, it is an advantage to rotate the arm so that the line of symmetry S is at an angle in excess of 90° (as shown in Figure 8b) and the centre of gravity of the weight 3 is forward of the axis of rotation X. This tends to push the nose of the boat down into the water which is an advantage when the boat is beating, i.e. hard on the wind. Figures 8a and 8c show two other possible positions of the weight 3. hi Figure 8c the weight is as far out to starboard as it can go. This might be the position chosen when the wind is on the starboard beam. With the wind on the starboard quarter, the weight might be positioned as shown in Figure 8a. Clearly, the weight could be rotated to equivalent positions on the port side of the hull and, in fact, to make any desired angle with the centre line C. When the vessel is maneuvering in tight curves, as when it is approaching a dock under motor, the arm is rotated to the aft position and the weight 3 will pivot automatically about the stub shaft 32 to a position in which it presents minimal lateral resistance to the vessel as it is making the turn.

A second example of the invention, ballast assembly 200, is shown in Figures 9 and 14a-14c. Most of the components of the assembly 200 are identical to those of the assembly 100 shown in Figures 1- 9. These identical components need not be described and carry the same reference numerals on both sets of Figures. Only the arm and the weight are modified. A lead weight 3 ' is rigidly attached to the outer end of an arm 2' the inner end of which is attached, also rigidly, to a shaft 1. While the assembly 200 is likely to be stronger and less costly than the assembly 100, it would have the disadvantage that the drag due to the weight 3' could be significant in any position of the weight other than at 90° to the centreline S.

Figures 4 and 6 illustrate a mechanism for bringing about the rotation of the shaft 1. In Figure 6 the arm 2 is shown as being positioned aft of the keel 7. The shaft is carried in a tube 6 that is mounted in the keel 7 and carries upper and lower bushes 8, 11 in which the shaft is rotatably seated. The upper end of the tube 6 projects into the interior of the hull to a height that is normally above the waterline 5. The upper end of the shaft is splined and tapered and projects out of the tube 6. Through the splines, a 'hat' or outer sleeve 15 integral with a bottom flange 16 is mounted on the upper end of the shaft and secured by a nut 13. The tube 6 is seated a bush 9 located in the sleeve 15 of the hat. The hat bears on a vertical thrust bearing pad 10 located between the flange 16 of the hat and a thrust plate 20 securely attached to stringers that are an integral part of the hull. The thrust plate takes the vertical force of the weight 3 that is transferred to the hull via arm 2, shaft 1, hat 15 and vertical trust bearing pad 10.

The lower end of the tube 6 terminates flush with the bottom of the keel 7. The lower end of the shaft 1 projects below the keel. The inner end of the arm 2 is fixed to the shaft. An end play ring 12 is mounted between the arm 2 and the bottom of the keel. The ring 12 copes with upward thrust applied to the arm. The bushes 8, 11 and the members 10, 12 are made of suitable engineering plastics and then^* construction and function is similar to that of the equivalent parts provided for mounting the rudders shafts in conventional sail boats.

A rope pulley 18 is fastened by screws 17 to the hat flange 16. An endless rope 19 is shown, in the present case, with two loops around the pulley 18.

The function of the bush 9 is to absorb radial forces applied by the ropes to the pulley 18. The vertical and torque forces are transferred via the hat and the tapered spline 14 and the nut 13 to the shaft. This construction allows the tube 6 to be extended to above the waterline 5. This eliminates the need for a packed gland type seal and the maintenance that that would require. It would still usually allow the mounting of pulley 18 and rope 19 underneath the floorboards of the hull

Figure 5 in particular shows the endless spliced rope 19 passing around spring loaded rollers 22 and a capstan winch 21 , both of the latter mounted in suitable known manner on the hull H. Only the vertical drum of the capstan winch is shown in the drawings. The winch is a commercially available, 12- volt component with a bidirectional capstan and a conical clutch between drive and drum. In the present case because, of the proximity of the hull, the capstan is mounted in upside down position with the drive motor above the rope drum. A suitable capstan winch is available from MUIR of Tasmania, Australia. The clutch operating mechanism has a spring-loaded device that holds the clutch in engagement up to a maximum torque setting. The clutch can slip when the maximum torque is exceeded. The clutch is released by a manually operated cable arrangement.

Structural details of the vessel, including its hull and keel have not been shown in more detail than is necessary for an understanding of the invention as these will be clear to experienced yacht designers and builders.

hi what follows, the example of a ballast assembly 100 is used to describe the operation of the invention. It will however be understood that, for the most part, the description could apply equally to the assembly 200 and the other ballast assemblies described herein. In operation, it is assumed at the start that the vessel is under sail, the weight 3 is out to windward and the vessel is preparing to tack, i.e. to steer through the wind. At or near the moment at which the sails start to unload and become slack and the vessel starts to right itself, the clutch on the capstan 21 is released. The weight 3, influenced by drag and then gravity, rotates about the axis X first aft and then to the leeward side. At this stage the clutch is re-engaged. The friction in the clutch slows the rotating motion of the weight and brings the weight to a gradual stop without undue shock loading on the vessel and the mechanism that carries the ballast. Yachtsmen are very capable of making a fine art of timing actions of this kind. If the friction in the mechanism is too great or the vessel speed is too low to cause the weight to start to swing, the capstan can be used to initiate the movement or position the weight a little aft before the tack.

After the rotation of Hie ballast is complete, the capstan can be used to position the weight exactly in the optimum position.

Alternatively the capstan can be used to drive and control the complete rotation.

If the yacht is in a race in which the use of electric (or any stored power) is not permitted, the capstan can be turned manually, using a winch handle in place of the electric motor.

If the mechanism as a whole is located below the floorboards and thus cannot be seen, a hole can be left in the boards so that the nut 13 at the top of the shaft is visible. The nut can be marked, for example with an arrow, to indicate the position of the weight 3. Alternatively, a simple sensor such as used in wind direction instruments could be mounted on top of the nut, This sensor could drive a modified wind indicator mounted with the other instruments normally found on yachts.

The time taken for the weight to rotate from one side of the vessel to the other may be reduced by executing the operation when the boat is travelling at high speed. In these circumstances, the fact that the boat is heeling (due to the wind force on the sails) allows gravity to assist the movement of the ballast and thus enables the movement of the ballast to be accomplished quickly. This maneuver would also allow for immediate powering up of the sails after the tack.

For a gybing maneuver, i.e.steering the vessel to make the wind pass from one side of the vessel to the other across the stern, the procedure is the same.

Maneuvering under motor and docking is best performed with the weight 3 rotated as far aft as it will go so that, athwartships, the vessel is level.

Sailing vessels and their crews encounter various hazards including storms, rough seas, rogue waves and collisions with submerged objects and marine life such as sunfish, whales and turtles. While no claim is made that a vessel equipped with a movable rotating ballast system as herein described could survive every hazard, the system has many features that could increase the likelihood of survival.

When the weight of the ballast assembly is out to the windward side, its righting moment increases almost up to the point of knock down

The centre of gravity of the weight 3 is relatively low and moreover, in the above- described systems, the weight is outside of, and below, the hull. It is therefore likely that, compared to crew on the rail and water ballast systems, the vessel is better equipped to ride rough seas.

A yacht can be completely overturned by a rogue wave or a big breaker that hits the yacht side on. A completely overturned yacht with conventional ballast has passed its angle of diminishing stability. This angle is around 120° for most yachts, hi other words, when a yacht is floating upside down, it is stable as it tilts between about 60° to either side. This up-side down stability can be reduced by releasing the brake on the rotating ballast system and allowing the weight to rotate freely to whatever is the lowest point, so that a much smaller wave would be needed to right the vessel.

The brake force of the capstan can be set so that, when a submerged object collides with the weight 3 or arm 2, or when the vessel grounds on the weight or arm, the brake will slip and the weight and arm will rotate out of the way. If the rope 19 or capstan brake fails, the weight 3 will rotate freely. Because the rotating ballast system can be designed so that the arc of rotation of the weight is not limited, the system has no components that come up against end stops. The shock load arising from this would be capable of destroying the vessel structure, as can happen in vessels provided with canting keels. In these conditions, the performance of a vessel equipped with a rotating ballast system as herein described will be greatly impaired but little direct danger is presented to the vessel.

If the arm 2 or shaft 1 fails, residual stability is still provided by the keel 7. The strength of the shaft and the arm as well as the weight of the keel 7 is a matter of design that would present no difficulty to a competent yacht designer.

The rotating ballast systems as herein described allow a yacht to be designed with relatively shallow draft. The strength of the systems is a matter of design.

Commercially available materials used commonly used in rudder headstocks can also be used for rotating ballast systems. The loads applied to conventional rudder headstocks are comparable to those applied to the shafts and bearings of the ballast systems herein described. However, the rudder of any vessel is in substantially continuous operation when the vessel is under way. Similarly, the types of rope and capstans currently in use on yachts are quite suitable for use in yachts provided with the rotating ballast systems described herein.

The shaft will usually be mounted so that the rotational axis X is theoretically vertical in both the athwartships direction and also the fore-and-aft direction when the hull is floating upright in the water. The advantage of this has already been explained. However, in certain circumstances, it may be advantageous to arrange that the axis X can be canted in the fore-and-aft direction and/or the athwartships direction. When the shaft is mounted in a fixed keel, as in the assemblies 100 or 200, the axis X would usually be canted permanently in the fore-and-aft direction. . One example of this is indicated by the dotted line X' in Figures 4 and 6. In Figure 4 the axis X' is canted forward. This could happen in a case in which the shaft is mounted in a keel that is arranged to swing backwards and forwards, as mentioned below. In Figure 6 the axis X' is canted in the aft direction. This could also happen in a case in which the keel is arranged to swing backwards and forwards but the shaft could also in some cases be fixed in this position. In the latter case, the maximum angle of cant is unlikely to be more than about 10°. However, the shaft could also be mounted in a canting keel (i.e. a keel that can swing in the athwartships direction) or even in a keel that can swing both athwartships and fore-and -aft. In these circumstances, the canting of the axis X would be temporary and, since the shaft cants with the keel, the angle through which it cants is likely to be considerably more than 10°.

A further alternative ballast assembly is shown in Figures 15a- 15c. In this case the weight and arm are integrally incorporated in a board shaped member 40. Furthermore, the member 40 could be attached to the shaft 1 at a downwardly canted angle of, say, 6°. That is, if the shaft were vertical, the outer end of the member 40 would be lower than the inner end. However, the shaft could also be canted forwards from the vertical at an angle of, say, 3°. That is, the upper end of the shaft is further forward than the lower end. Clearly either or both of these angles could vary in either direction or be absent. This arrangement provides a number of trimming options. With the member 40 extending outwardly from the centre line C to its maximum, the general plane of the member 40 is canted at 3° to the direction of travel with the leading edge of the member 40 lower than the trailing edge. This will result in a downwardly acting force on the member 40, increasing the righting moment. Moving the member 40 further forward will rapidly increase the angle and the downward force. Moving the member 40 backwards through 45° will result in the board being horizontal and it will apply a zero downward force. Moving the member 40 fully aft will result in the member 40 being canted downwardly at 3° so that it will apply a lifting force to the vessel. However the centre of gravity of the member 40 has also, by the same movement been moved back and this will probably apply a downward force to the vessel that is greater than the lifting force. This fully aft position could therefore provide an advantage when the vessel is sailing directly before the wind, tending to push the stern of the vessel down in the water.

The optimum degree of canting of both the shaft and the member 40 can be established by experiment. The challenge for the naval architect will be to optimise all these factors including minimising drag, especially through the design of the arm , the weight and/or the member 40.

Yet another alternative is illustrated schematically in Figure 13. This shows a twin keeler with each keel equipped with its own rotating ballast system. The general nature of these systems will be clear from the foregoing description.

The rotating mechanism can be fitted with a seal allowing it to fit in its entirety under the floorboards. The shaft can also be extended to go through the deck allowing the operating mechanisms to be installed above decks. This is illustrated schematically in Figure 11.

Figure 11 also shows that an arm 50 carrying a weight 52 could be mounted directly under the hull. This system could be used in conjunction with daggerboards or forward rudders in the same way as these components are used in yachts provided with canting keels. The system could even be designed so that part of the arm 50 comes out of the water when the vessel heels, again as shown in Figure 11.

In a modification to the assembly 100, the weight 3 could be mounted in such manner that the weight is not free to rotate on the stub shaft 32. This rotation could, for example, be controlled so that the weight is forced to remaining pointing in a desired direction irrespective of the angular position of the arm 2. This could be achieved in one way by providing that the shaft 1 and the stubshaft 32 are both hollow, each having a bore in which are housed internal control shafts. The arrangement further comprises two sprocket wheels of equal diameter, one fixed to the lower end of the internal control shaft housed in the shaft 1 and the other fixed to the upper end of the internal control shaft housed in the bore of the stub shaft 32. The weight 3' is fixed to the lower end of the later control shaft. The sprocket wheels would be connected together by a sprocket chain housed in the arm 2. The angular position of the weight 3, relative to the arm 2, would then be controllable by rotating the upper end of the control shaft the passes through the shaft 1. A hydraulic ram or a system of rods arranged parallelogram fashion connected to a crank mounted on the weight 3 could also be used to achieve a system for controlling the angular position of the weight on the stub shaft 32.

Many alternative drive mechanisms for any of the rotatable ballast systems described herein are possible, including gears, chains, hydraulic rams or motors. The control systems could incorporate sensors and computers. On smaller vessels the system could be as simple as a tiller directly attached to the shaft 1.

It is also envisaged that the weight could be slidably mounted on the arm to increase or decrease the righting moment. A similar effect could be achieved by providing an arm that is telescopically extendable. The arm would comprise one member slidably inserted in another. The extension could be achieved by a system of ropes and pulleys, a hydraulic ram or one or more electrically or manually driven screw threaded rods. In a very simple and inexpensive version the one member could be moved manually inside the other and held in place with a clamp or retaining pin. This might be suitable for a trailer sailor.

If appropriate, wings and/or wing tips could be provided for hydrodynamic or other reasons, for example on the weight or at the inner end of the arm, adjacent the shaft. .

Still another alternative is illustrated in Figure 12. Here, the weight 3" and arm 2" are mounted inside the vessel adjacent the upper end of a shaft 1" that extends upwardly from the bottom of the vessel. This system presents an alternative to water ballast. Clearly precautions would have to be taken to prevent injury to the crew when the ballast rotates. For example, the weight 3" and arm 2" could be housed in a protective housing built into the vessel.

Any of the rotating ballast assemblies as described herein could be mounted on a keel that is itself arranged to move backwards and forwards. Keels that can slide backwards and forwards are already being mounted on some yachts. In the present case it is envisaged that the keel could alternatively be mounted on a transversely positions shaft so that the keel could swing forwards and backwards about the shaft, controlled, for example, by a hydraulic ram. This movement would alter the hydrodynamic forces to either increase righting moment or create lift or reduce draft.

For similar reasons, the rotating ballast assemblies as described herein could be mounted on a lifting keel or a canting keel.

The rotating ballast assemblies could be used in combination with many other known underwater appendages such as forward daggerboards, forward or rearward rudders, leeboards, canting keels or canting daggerboards The assemblies could also be used in multiples, for example in twin keelers or in tandem or even on multihulls.

The control mechanism to rotate or brake the shaft can take many forms including chain drives, hydraulic drive motors or rams, ratchet or friction drives. The rotation and/or braking could also be automated using electrical or electronic control mechanisms. The rotation and/or braking could be activated by using the forces applied by the sails to the sheets, i.e. the lines that control the sails.

It is not intended that recognised mechanical equivalents of and/or modifications of and/or improvements to any matter described and/or illustrated herein should be excluded from the scope of a patent granted in pursuance of any application of which this specification forms a part or which claims the priority thereof or that the scope of any such patent should be limited by such matter further than is necessary to distinguish the invention claimed in such patent from the prior art.

Claims

1.

A vessel comprising a hull arranged to be provided with movable ballast, the ballast comprising a ballasting member arranged to be attached to a mounting member mountable in the hull in such manner as to be rotatable about an axis of rotation that is upright in a direction athwartships of the hull when the hull is upright in the same direction, means being provided for attaching the ballasting member to the mounting member in a position in which the centre of gravity of the ballasting member is offset from the axis of rotation.

2

A vessel according to claim 1, in which the hull has a keel through which the mounting member is arranged to pass.

3.

A vessel according to claim 1, in which the means for attaching the ballasting member to the mounting member comprises an intermediate member that projects transversely from the mounting member and spaces the ballasting member from the mounting member.

4.

A vessel according to claim 3, in which the intermediate member is perpendicular to the axis or rotation.

5.

A vessel according to claim 3, in which the ballasting member is rotatably mountable on the intermediate member.

6.

A vessel according to claim 3, in which the ballasting member is mountable on the intermediate member in such manner as to be capable of rotating about a rotational axis that is substantially parallel to the axis of rotation of the mounting member.

7.

A vessel according to claim 5, in which the ballasting member is free to rotate with respect to the intermediate member about the rotational axis.

8.

A vessel according to claim 6, in which the ballasting member has a centre of gravity that is located on, or close to, the rotational axis.

9.

A vessel according to claim 8, in which the ballasting member is so shaped and mounted as to be able to rotate about the rotational axis to a position in which drag due to the ballasting member as the vessel moves through the water is reduced.

10.

A vessel according to claim 3, in which the intermediate member has a longitudinally extending axis of symmetry.

11. A vessel according to claim 10, in which the ballasting member is rigidly mountable on the intermediate member.

12.

A vessel according to claim 3 in which the ballasting member and the intermediate member together have the shape of a foil having a longitudinally extending axis of symmetry.

13.

A vessel according to claim 1, in which the mounting member is rotatable to either side of the fore-and-aft direction of motion of the vessel about the axis of rotation.

14.

A vessel according to claim 1, in which the mounting member is rotatable about the axis of rotation through an angle in excess of 90° to either side of the fore-and-aft direction of motion of the vessel.