1. Technical Field
This invention relates to a sail configured to fly in its working shape while being lighter and having less drag relative to its lift characteristics, than conventional sails. In spinnaker and jib embodiments, the sail may have a better ratio of lift to heeling moment, and allow tighter sheeting angles with less backwinding of the mainsail, respectively.
2. Background Information
Sails used on sailboats (and on wind powered craft in general) propel the boat in substantially all points of sail other than perhaps dead downwind, by creating “lift”. Those skilled in the art will recognize that “lift” is a low pressure zone on one side of the sail that is created by wind blowing over the convex surface of a sail when disposed in its working (flying) shape. This flying shape thus resembles a foil or airplane wing shape, to draw the craft from the high pressure area on the concave side of the sail, to the low pressure area on the convex side, to move the craft forward. The structure of the sail itself creates drag as it moves through the air, which tends to resist the forward motion of the craft.
It is desirable to provide a sail that provides a relatively large lifting force with a relatively low drag force.
According to one aspect of the invention, a sail for a wind-powered craft includes a web which forms a flying shape upon engagement with the wind, the web including a combination of wind-impermeable and wind-permeable portions disposed between the leading and trailing edges, wherein the web has a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.
According to another aspect of the invention, a sail for a wind-powered craft includes: a head portion configured for being coupled to an upper end of a mast; a tack portion configured for being coupled to a deck, bowsprit, or spinnaker pole of the craft; and a clew portion configured for being coupled to one or more control lines for trimming the sail. A web supported between the head, tack and clew portions includes a combination of one or more wind-impermeable portions in the form of fabric or similar material, and one or more wind-permeable portions in the form of widely spaced strings or lines, the wind-permeable portions extending from the clew portion on a trailing portion of the sail. A ratio of the wind-permeable portions to wind-impermeable portions is within a range of about 10-40 percent. The sail is asymmetrical, or symmetrical wherein wind-permeable portions are disposed symmetrically on opposite sides of the sail with the clew and tack portions being interchangeable depending on the orientation of the craft.
In still another aspect of the invention, a method for configuring a sail for providing wind-powered motive force to a craft, includes configuring a web for forming a flying shape upon engagement with the wind, the flying shape extending from a leading edge to a trailing edge. The method also includes providing the web with a combination of one or more substantially wind-impermeable portions and one or more substantially wind-permeable portions disposed between the leading and trailing edges. The web is provided with a permeability ratio of wind-permeable area to wind-impermeable area within a range of about 5 to 80 percent.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.
The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific aspects in which the invention may be practiced. These aspects are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other aspects may be utilized. It is also to be understood that structural, procedural and system changes may be made without departing from the spirit and scope of the present invention. In addition, well-known structures, circuits and techniques have not been shown in detail in order not to obscure the understanding of this description. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
Where used in this disclosure, the term “axial” when used in connection with an element described herein, shall refer to a direction which is substantially parallel to the longitudinal axis of a wind-powered craft, such as axis a of
Referring now to
The present inventor has recognized that in many sails, under many operating conditions, an area extending from the clew 22 in substantially all directions along the sail (hereinafter the “clew area” or “clew portion”) provides a relatively small amount of the total lift provided by the sail. This clew area may vary in size, depending on sail trim and specific shape of a given sail. In particular examples, it may be as large as substantially all of the axially extending portion of the sail, e.g., in the event the sail is a spinnaker. In the case of a jib, this clew area may be the trailing portion of the sail that shows “return” (i.e., is backwinding the mainsail) when the jib is tightly trimmed. A mainsail may also exhibit such a clew area under particular trimming conditions.
Turning now to
As shown in
In the particular examples shown, the wind-permeable portions 30 may take the form of a system of “strings” 32 that allow air to pass through, and which are disposed so that the portions 30 effectively extend from the clew 22 in substantially all directions, to form the “clew area”. The size and shape of the “clew area” of a particular sail may vary depending on the sail's purpose (runner, reacher, jib, etc.) and anticipated application, as will be discussed in greater detail hereinbelow. Moreover, as discussed above, the area of fabric removal need not extend continuously as shown, but may be discontinuous, e.g., disposed as a series of patches disposed in spaced relationship to one another along the sail. The wind permeable portion also may not necessarily include the clew 22 itself. In particular embodiments, however, the wind-permeable portion is disposed closer to the trailing edge or leech 34 of the sail, than to the leading edge 36 of the sail, as best shown with respect to sail 12′.
As mentioned, the size of the wind-permeable portion is not limited to those shown in the Figures, but rather, may depend on various factors, such as the sail type (e.g., main sail, jib, spinnaker, runner, reacher, etc., including whether the sail is asymmetrical or symmetrical), the particular application, including type of craft (e.g., sailboat) and the trim or wind direction relative to the direction of movement of the craft.
In particular aspects of the invention, the wind-permeable portion(s) is sized and shaped to provide the sail with a ratio of the wind-permeable portion(s) to wind-impermeable portion(s) (hereinafter, the “permeability ratio”) within a range of about 5 to 80 percent. In other aspects, the ratio may be within a range of about 10 to 40 percent. Moreover, in various aspects, the wind-permeable area may extend, in a direction substantially parallel to the foot 37 of the sail, a distance between about 2 to 50 percent of the length of the foot. In particular embodiments, this distance may be between about 5 to 20 percent of the length of the foot. The wind-permeable area may also extend, in a direction substantially parallel to the leech 38 of the sail, a distance between about 2 to 95 percent of the length of the leech. In particular embodiments, this distance may be between about 5 to 60 percent of the length of the leech.
It is contemplated that in particular embodiments, the ratio of wind-permeable to wind-impermeable portions will be fixed for a given sail, and that users may simply maintain an inventory of sails of different ratios. The user may then choose from among the sails of various ratios, e.g., based on current wind conditions, etc.
In other embodiments, instead of a fixed ratio, sails may be provided with a variable ratio, such that a user may adjust the ratio of a particular sail. For example, a sail may be provided with a series of removable web portions, which may be selectively removed and replaced by the user, such as may be desired to respond to changing wind/weather conditions. Alternatively, in the event the wind-permeable portions are formed by a series of lines or strings as shown, such lines may be configured for being lengthened or shortened to change the shape of the sail, and/or to change the permeability ratio. These lines, whether of fixed length (for fixed ratio) or adjustable length (for variable ratio), may terminate at the clew 22 (e.g., at a clew ring or similar attachment point) of the sail as shown, where they may be connected to a conventional control sheet.
As mentioned above, the size, shape and ratio of the wind-permeable area for a particular sail may be configured based on the desired application, and may thus depend on factors such as the intended sail shape/function, intended sheeting angle, and/or angle of attack to the wind.
It should also be recognized that in accordance with the teachings hereof, the wind-permeable area may be applied to substantially any portion of the sail to which wind is not expected to be “attached” during its anticipated operation. One skilled in the art will recognize that such areas may be identified by examining telltales along the body of a conventional sail. The area of non-attached flow along, for example, the foot and leech of the sail in the embodiments shown in
The sail, including both the wind-impermeable and wind-permeable portions may be fabricated from any number of suitable materials. The wind-impermeable portions may be fabricated from any number of materials conventionally used for sails, including fabrics made from natural or synthetic fabrics, plastics, composite materials, mixtures of the same, and/or laminates of the same. Examples of such materials include synthetic materials such as: polyamide (Nylon); polyethylene terephthalate such as DACRON® (DuPont); aramid such as KEVLAR® (DuPont), TWARON® (Teijin Aramid), and TECHNORA® (Teijin Aramid); carbon fiber; HMPE (high molecular weight polyethylene) such as SPECTRA® (Honeywell), and DYNEEMA® (DSM IP Assets B.V.); thermoset liquid crystalline polyoxazole, such as ZYLON® (Toyo Boseki Kabushiki Kaisha Corporation), etc.
These same materials may be used to fabricate the lines or strings of the wind-permeable portions. In this regard, the lines may be fabricated from substantially any material capable of supporting the load (e.g. spectra) of the sail. The number of strings and associated attachment points may vary depending upon the load and desired working (flying) shape of the sail.
As mentioned above, it should be recognized that aspects of the present invention may be applied to symmetric, as well as asymmetric, sails. The embodiments shown and described hereinabove with respect to
Turning now to
In this alternate embodiment, both of the “clew areas” of the sail, i.e., those areas on opposite sides of the sail that alternate between clews and tacks depending on the orientation of the craft, may be replaced with strings or other wind-permeable portions 30′ as shown.
This approach effectively permits an otherwise conventional asymmetric spinnaker to be configured as a symmetric spinnaker in which the conventional head 18 is attached to the mast as shown, while the tack is replaced by an attachment 40 to the bow sprit in the middle of the foot 37 of the sail. The foot may be attached centrally to the bow sprit or alternatively, may be configured to slide along the bow sprit, e.g., between points “A” and “B” as shown, to provide the sail with greater range of movement from side to side of the boat.
It should be recognized that aspects of the invention may include various placements and shapes of the particular areas defined by the removed sail fabric. Although the present invention has been described with reference to specific exemplary aspects, it will be evident that various modifications and changes may be made to these aspects without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
In addition, although the present invention has been described with reference to sails used to move a sail boat, it should be recognized that aspects of the present invention may be applied to substantially any type of craft configured to support a flexible material in a working shape configured to generate a motive (lift) force. Examples of such craft may include various types of sail boats ranging from sail boards and kite surfers to large multi-masted vessels, and various aircraft, including gliders, hang gliders, ultra-light aircraft, parachutes, powered parachutes, etc.
It should be further understood that any of the features described with respect to one of the aspects or embodiments described herein may be similarly applied to any of the other aspects described herein without departing from the scope of the present invention.
This application claims the benefit of U.S. Provisional Patent Application Ser. Nos. 61/712,458, entitled Structural Support Scheme for the Replacement of the Clew Section of Sails, filed on Oct. 11, 2012, and 61/721,054, entitled A Structural Support Scheme for the Replacement of the Clew Section of Sails, filed on Nov. 1, 2012, the contents, both of which, are incorporated herein by reference in their entireties for all purposes.
Number | Date | Country | |
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61712458 | Oct 2012 | US | |
61721054 | Nov 2012 | US |