EP0094661A2 - Sail mast - Google Patents

Abstract

Mast (1) having essentially a rectangular cross-section with rounded narrow sides, preferably made in sandwich-type construction from integrally fiberglass-reinforced polyurethane structural foam (7) as core material with fiberglass laminates (8) as stressed skins bonded to both wide sides. The depth measured between the two narrow sides is greatest in the vicinity of the attachment area of the wishbone-type boom (12), and it decreases from there towards at least the top end, whereby the average depth of the mast cross-section shall measure at least twice as much as the mast width. The mast (1) for a sail-board is connected with the wishbone-type boom (12) via an articulated attachment (13) thus permitting the mast to pivot freely within the limits of the wishbone boom and to point its narrow leading edge against the wind. The mast (1) is essentially submitted only to a stress resulting from the tractional force of the sail (14) attached behind the narrow backside of the mast. The mast (1) possesses a much higher breaking strength and stiffness edgeways than conventional round tubular masts. Furthermore, the narrow flat mast (1) has a drastically reduced frontal area and is therefore aerodynamically much more efficient as well as lighter in weight than a conventional round mast.

Description

The invention relates to a mast for a sail, in particular for the sail of a watercraft in Kat rigging without foresail, such as a sail board or small dinghy.

The simplest form of a sail mast is a mast with a round cross-section, which is usually tapered from bottom to top. In light sailing vehicles such as laser dinghies and sailing boards that are driven without a foresail, glass-fiber reinforced plastic is often used as the material for the mast. If the tubular mast is round in cross-section, you have to compromise on the diameter, because on the one hand you want to have a sufficiently rigid mast so that it does not deform and increase buoyancy when the wind pressure on the sail is increased, and on the other hand you want to have a mast that is as slim as possible and that opposes the air flow as little resistance as possible, so that the turbulence of the air behind the mast is as low as possible, so that the sail is largely laminar. In order to avoid the disadvantages of an insufficiently rigid mast, which leads to deformation of the sail and loss of buoyancy when the wind pressure is increased, the light sailing vehicles mentioned have also been equipped with stiffer aluminum tube masts, but the disadvantage is again to be accepted whose breaking strength is significantly lower. If the price is irrelevant, slim tube masts with high rigidity can also be made from high-quality materials such as carbon and Kevlar fibers.

In order to achieve the most favorable aerodynamic shape of the mast, masts with a streamlined cross-section, such as an oval or drop-shaped cross-section, have also been produced. However, the mast is always cantilevered by shrouds, with the adjustment of the mast absorbing most of the bending forces acting on the mast, so that it is possible to make the mast very slim. A real advantage with regard to the air flow on the mast and on the sail can only be achieved with a mast with an aerodynamic cross-section if the mast is rotatably positioned within the boat hull within a limited range, so that it can be rotated in the correct direction of flow together with the sail . Such masts with a streamlined cross-section are known in high-performance sailing vehicles such as catamarans, sand sailers or ice sailers, in which the aerodynamic conditions are particularly important because of the very high speeds that can be achieved.

The light sailing vehicles already mentioned, such as Laser dinghies and sailing boards have open-ended masts, which for reasons of weight are mostly hollow and have a round cross-section or a width / depth ratio of about 1: 1, so that these masts have roughly identical strength and rigidity in all bending directions.

With a sail system there are similar conditions with regard to the air flow as with a rigid wing, which is why the sail system is also referred to as buoyancy. In both cases there is a flow through the air, the deflection of the flow being converted into lift, and in both cases it is a question of using a given air flow with little air resistance to generate as much lift as possible. In the case of a rigid wing, however, the buoyancy force is transmitted via the rigid construction to the support bar inside the wing, so that the latter is subjected to bending in the direction of lift. Compared to a rigid wing, however, the components of a sailing rig have a lot of mutual flexibility so that the forces have a different effect. The aerodynamic buoyancy acting on the flexible sail fabric results in increased tension on the bulging sail. A tensile force therefore acts on the mast from the sail, in the direction in which the sail extends backwards from the mast.

The invention is therefore based on the consideration that the pulling force exerted by the sail is the force which normally acts on the mast and which stresses the mast on bending. So far, the disadvantage of masts which are too flexible and which bend under increased wind pressure, as a result of which the sail profile changes unfavorably, has been countered by increasing the rigidity of the mast with a thicker mast cross section. However, this increases the air resistance again and the weight of the mast and the turbulence of the air flow increase. Attempts have therefore also been made to achieve increased stiffness with other materials, for example by using light metal or carbon fibers. However, a mast made of light metal has a low yield point and if it is not tolerated, it can easily buckle, while a mast made of carbon fibers is very susceptible to damage and is also very expensive.

The invention is therefore based on the object of an open-ended mast with optimum flexural strength and breaking strength in the normally occurring To create load direction, which also has a low air resistance in the direction of flow. Furthermore, the mast should be inexpensive to manufacture, light and unsinkable. This is achieved by a mast with the features listed in claim 1 1. Seen from the front, the mast is narrow and has a depth that is considerably greater than its width, whereby the tensile force exerted by the sail stresses it like a beam lying on edge. Since the air flow acting on the sail rig mostly has the same direction as the direction of the sail directly behind the mast, the narrow mast has the advantage that the air flow experiences minimal resistance and the flow over the sail remains largely laminar, since behind the Mast hardly a swirl of air can take place.

In a preferred manner, a mast for a sail board, in which a boom is connected to the mast, has the largest cross-section in the fastening area of the boom, which is made smaller at least towards the upper mast end. In a preferred further embodiment, such a mast is pivotally connected to the boom at its front edge and can be freely pivoted within the boom so that it can assume the correct position for the wind together with the sail attached to the rear longitudinal edge.

With the mast having the features of claim 1, which is subjected to bending by the pulling force exerted by the sail in the direction of the longer axis of the cross section, an apparently prevailing prejudice with regard to the loading method was overcome, because of the similarity already mentioned between a rigid wing and an open-ended sailing rig, it has previously been assumed that the sail mast, like the supporting beam of a wing, is stressed in the direction of buoyancy, i.e. transversely to the direction of travel, because there are sailing dinghies with non-worn-out sailing rigs, the mast of which is transverse has a larger cross-section to the boat axis than in the boat's longitudinal axis.

• Fig._' 1 einen Mast für ein Segelbrett in der Ansicht von vorn;
• Fig. 2 den Mast gemäss Fig. 1 in Seitenansicht;
• Fig. 3 - 5 in grösserem Masstab dargestellte Querschnitte des Mastes gemäss Fig. 1 und 2 in verschiedener Masthöhe;
• Fig. 6 einen herkömmlichen, im Querschnitt kreisförmigen Mast auf einem Surfbrett von der Seite gesehen;
• Fig. 7 den flachen erfindungsgemässen Mast aus der gleichen Blickrichtung wie Fig. 6;
• Fig. 8 und 9 einen herkömmlichen und einen erfindungsgemässen flachen Mast auf einem Surfbrett von vorn gesehen;
• Fig. 10 die Strömungsverhältnisse am Mast, der einen negativen Anstellwinkel zum Wind einnimmt;
• Fig. 11 die Verbindung zwischen Mast und Gabelbaum auf einem Segelbrett

Further details and advantages result from the following description and the drawings, in which embodiments of the subject matter of the invention are shown purely by way of example. Show it:

• Fig. _'1 a mast for a sailboard in front view;
• 2 shows the mast according to FIG. 1 in a side view;
• 3 - 5 cross sections of the mast according to FIGS. 1 and 2 shown on a larger scale at different mast heights;
• 6 is a side view of a conventional mast with a circular cross section on a surfboard;
• 7 shows the flat mast according to the invention from the same viewing direction as FIG. 6;
• 8 and 9 a conventional and an inventive flat mast on a surfboard seen from the front;
• 10 shows the flow conditions on the mast, which assumes a negative angle of attack to the wind;
• Fig. 11 shows the connection between mast and boom on a sailing board

The mast 1 according to FIGS. 1 and 2 is intended for a sail board and is rotatably mounted in the sail board with a mast foot 2 at the lower end. From Fig. 1 it can be seen that the mast seen from the front over the entire mast height constant width. According to FIG. 2, however, the mast 1 has a cross section that is variable over the mast height, only the depth of the mast changing. At about a third mast height, the mast has an area 3 with the greatest mast depth, since here the mast is connected to the boom of the sailing board, not shown in the drawing, and the greatest stress occurs. In area 3 the mast has several eyelets 4 for connection to the boom. The area 5 of the mast which adjoins at the bottom has a gradually decreasing cross section, only the depth of the mast gradually decreasing. In the same way, in the region 6 of the mast adjoining at the top, the cross section decreases toward the upper mast end. The cross sections of the mast 1 in the areas 3, 5 and 6 are shown on a larger scale in FIGS. 3-5.

An embodiment of such a mast for a sail board that has been tried and tested has a mast height of 4.5 m and a constant width of the mast of 22 mm over the entire height. The depth of the mast is 40 mm above the mast foot 2, 80 mm in the fastening area 3 for the boom and 35 mm at the upper end. The mast preferably consists of a sandwich construction made of glass fiber reinforced rigid polyurethane foam with unidirectional fiberglass laminates glued on the side. The mast has a weight of approx. 2.3 kg. Compared to a round mast commonly used, this mast has the following advantages: The front surface is reduced by 0.1 m2, ie by 50%, the mast is about 10% lighter and about three times as stiff in the direction of loading round mast, ie the break resistance is much higher. The mast is aerodynamically much more effective and since the mast none If there are any cavities that need to be sealed, the mast can float easily. In an advantageous method of manufacture, sandwich boards are produced from the materials mentioned, from which masts with the desired bending line are then formed by sawing, the edges or narrow sides being rounded off with the aid of a milling cutter and protected by a plastic coating. Compared to a tubular mast, this method of production has the advantage that the desired bending stiffness can be determined by the type of cut. It can be seen from FIGS. 3 to 5 that fiberglass laminates 8 are glued to the rigid polyurethane foam core 7 on both long sides.

The mast made of a rigid polyurethane foam core also has the further advantage that you can easily make holes for screws for attaching fittings, etc., without having to make sure that the mast is also sealed in order to be able to float, which is the case with one Pole mast always requires measures.

The behavior of the flat mast according to the invention in connection with a sail in the wind is shown in FIGS. 7 and 9, in which the mast is shown on a surfboard viewed from the side or from the front. For comparison to this, FIG. 6 shows a view corresponding to FIG. 7 of a conventional tubular mast with a circular cross section and a side view on a sailing board and it can be seen that, in contrast to this conventional mast, the flat mast according to the invention according to FIG Effect of the forces acting on it experiences the intended deflection. This can be seen even more clearly in the comparison of FIGS. 8 and 9, which make it clear that a conventional mast with a circular cross-section turns in the upper region The leeward side bends, while the flat mast according to the invention bends intentionally in the upper region towards the windward side. It can be seen that the mast which bends in the manner described results in a more favorable curvature of the sail and thus more forward performance is achieved.

From the relevant literature it can be seen that a sail profile with a round mast at the front edge of the sail produces 15% less buoyancy compared to the same sail profile without a round mast, and on the other hand it has more than 50% more air resistance. These values apply to wind speeds of the apparent wind of 18 km / h. Since modern sailing boards glide over the water at more than 40 km / h, whereby the apparent wind should reach a speed of approx. 70 km / h, one can imagine that with the mast described above, the propulsive power can be doubled at higher speeds compared to a sailing vessel with a round mast, which is a significant improvement.

In Fig. 10 it is shown schematically that the flat mast according to the invention assumes a negative angle of attack with the wind, so that an increased profile curvature is achieved at the leading edge of the wind, which allows a more direct flow at a flatter angle of the air than with. a conventional mast with a circular cross section according to FIG. 10a is possible, in which the air flow is set in turbulence immediately behind the front edge, as a result of which propulsive force is lost. In contrast, a largely laminar flow occurs with the flat mast.

Another advantage of the flat mast is that it tends to dodge sideways and bend over the flat side, so that an increased deformation is possible, which reduces the risk of breakage of the mast. Such an excessive load occurs, for example, when a large wave crashes into the sail in the sea surf. In contrast, tubular masts that are equally stiff in all directions cannot deflect under such a load and buckle with less deformation.

From FIG. 11 it can be seen that in the case of a flat mast 1 for a sailing board, the connection of the mast in the boom 12 is carried out via a pivotable connection 13 such that the mast can oscillate freely around this connection 13 within the boom 12 and therefore always with the narrow side against the wind, so that the sail 14 adjoining the rear narrow side of the mast can assume the position shown in FIG. 10. With the help of side ropes 15 the position of the mast can be influenced in order to achieve a certain trimming effect, e.g. a higher curvature of the sail profile in the front part.

Finally, with the mast described above, the sailing property can also be improved by changing the depth of the sail profile by using the mast, whose rear profile line according to FIG. 2, for example, is straight and whose front profile line is curved, can also be rotated by 180 ° , so that the front and rear narrow sides swap their position with respect to the subsequent sail. The sail of a sailing board, which is designed with a hem as a mast pocket, is given the above-described possibility of also being able to use the mast rotated due to the predetermined cutting of the sail on the luff, in one position of the mast a different profile depth or curvature than in the other position.

Claims (7)

1. mast for a sail, in particular for the sail of a sail board, characterized in that the unsupportable, rotatable and pivotable supportable mast (1) has an elongated cross section in which the ratio of the arithmetic mean of the longitudinal axes of the cross sections variable over the mast height to the transverse axis is at least 2.5 such that the mast is so flexible in the transverse direction that it bends concavely towards the windward side under the action of the forces acting on it. 2. Mast according to claim 1, characterized in that the mast (1) for use in a first and in a second position rotated by 180 ° on the opposite narrow sides of differently shaped profile lines, for example on one narrow side a straight and on the opposite Narrow side has a convex profile line. 3. Mast according to claim 1, characterized in that it consists of a composite construction of glass fiber-reinforced polyurethane rigid foam (7) with fiber-reinforced synthetic resin (8) glued on the outside. 4. Mast according to claim 1 for a sail board, in which a boom is connectable to the mast, characterized in that the mast (1) in the region of its largest cross section has fastening means (4, 13) for connection to the boom (12) , and that the cross section of the mast from said mounting area at least to decreases at the top of the mast. 5. Mast according to claim 4, characterized in that it can be connected via a pivotable connection (13) arranged on its front edge to the boom (12) in order to be freely pivotable within the boom. 6. Mast according to claim 1, characterized in that the longitudinal axis of the mast (1) assumes a negative angle of attack with respect to the air flow acting on the mast connected to a sail. 7. Mast according to claim 1, characterized in that the average length of the transverse axis of the mast cross section is not more than 0.7% of the mast height.

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