Abstract:
The sail force gauge utilizes an electronic system to measure the vectored force of the mainsheet or jib sheet. By gaining the vectored force of the sheet, a relative vectored force upon the sail can be acquired thru simple trigonometric equations. To obtain the vectored force measurement, a multi-axis load cell will measure the force in the lateral and axial directions. These forces can be used to calculate the vectored force of the mainsheet. By knowing the dimensions of the boom length, the sheet block positions, and the vector angle, the resultant angle of the boom can be calculated as well as the perpendicular sail force acting upon the boom. From these calculations, the relative axial force acting upon the boat can be calculated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. patent application Ser. No. 61/582,436, entitled “ELECTRONIC DEVICE FOR MEASURING THE RELATIVE FORCE ACTING UPON A SAIL”, filed on 2 Jan. 2012. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention is related to sailing boats. More specifically, the present invention is related to an electronic device for measuring the force acting upon a sail by measuring the angle and force acted upon the sail “sheet” or rope. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sailing is the propulsion of a vehicle and the control of its movement with large (usually fabric) foils called sails. By changing the rigging, rudder, and sometimes the keel or center board, a sailor manages the force of the wind on the sails in order to move the vessel relative to its surrounding medium (typically water, but also land and ice) and change its direction and speed. 
         [0004]    Sails on sailboats act as air foils and utilize the wind and force created on the foil to provide forward force for the boat. The force resultant from the sail is based on a number of factors including the speed of the wind, the aerodynamic shape of the sail (foil), and the angle of the sail or foil relative to the wind. Trained sailors with experience understand the balance of these variables. Through manipulation of these variables they attempt to produce the optimal forward force on the boat, which is not readily known to the sailor. Only by gleaning information on how the boat feels, position of simple telltales, or gauging by the relative speed of the boat does the sailor know to adjust the sail setup. The novice attempts to set the sail, but only by guess due to the lack of any performance indication. This provides a barrier to entry for the untrained boater, who would shy away from the experience due to lack of skill. 
       DEFINITIONS 
       [0005]    In sailing, a sheet is a line (rope, cable or chain) used to control the movable corner(s) (clews) of a sail. 
         [0006]    In most cases, rope is the term used only for raw material. Once a section of rope is designated for a particular purpose on a vessel, it generally is called a line, as in outhaul line or dock line. A very thick line is considered a cable. 
         [0007]    Lines that are attached to sails to control their shapes are called sheets, as in mainsheet. If a rope is made of wire, it maintains its rope name as in ‘wire rope’ halyard. 
         [0008]    Lines (generally steel cables) that support masts are stationary and are collectively known as a vessel&#39;s standing rigging, and individually as shrouds or stays. The stay running forward from a mast to the bow is called the forestay or headstay. Stays running aft are backstays or after stays. 
         [0009]    Moveable lines that control sails or other equipment are known collectively as a vessel&#39;s running rigging. Lines that raise sails are called halyards while those that strike them are called downhauls. Lines that adjust (trim) the sails are called sheets. These are often referred to using the name of the sail they control (such as main sheet, or jib sheet). 
         [0010]    A boom is a spar (pole), along the foot (bottom) of a fore and aft rigged sail, which greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. The boom also serves an attachment point for more sophisticated control lines. Because of the improved sail control it is rare to find a non-headsail without a boom. In some modern applications, the sail is rolled up into the boom for storage or reefing (shortening sail). 
         [0011]    The genoa or jenny was originally referred to as the ‘overlapping jib’ or the Genoa jib. It is a type of large jib or staysail used on Bermuda rigged craft that overlaps the main sail, sometimes eliminating it. It is used on single-masted sloops and twin-masted boats such as yawls and ketches. Its large surface area increases the speed of the craft in moderate winds; in high wind conditions a smaller jib is usually substituted, and downwind a spinnaker may be used. The feature that distinguishes a genoa from a jib is that the former extends past the mast, overlapping the mainsail when viewed from the side. 
         [0012]    Reefing is a sailing maneuver intended to reduce the area of a sail on a sailboat or sailing ship, which can improve the ship&#39;s stability and reduce the risk of capsizing, broaching, or damaging sails or boat hardware in a strong wind. 
       SUMMARY OF THE INVENTION 
       [0013]    The sail force gauge utilizes an electronic system to measure the vectored force of the mainsheet or jib sheet. By gaining the vectored force of the sheet, a relative vectored force upon the sail can be acquired thru simple trigonometric equations. To obtain the vectored force measurement, a multi-axis load cell will measure the force in the lateral and axial directions. These forces can be used to calculate the vectored force of the mainsheet. By knowing the dimensions of the boom length, the sheet block positions, and the vector angle, the resultant angle of the boom can be calculated as well as the perpendicular sail force acting upon the boom. From these calculations, the relative axial force acting upon the boat can be calculated. 
         [0014]    This calculated forward force can be displayed as a passive gauge for the sailor to utilize for self-adjustment. It can also be used to calculate the differential measurement of angle and force and where the optimum sail position is by displaying a message to adjust the mainsheets “in” or “out”. Wind speed and wind angle can be utilized in the calculations to “learn” the optimum angle of attack for that sail and boat. 
         [0015]    The calculated forward force can also be used with automatic sheet winches to automatically adjust the sheet for the optimum forward force or used with an autopilot to self-steer and self-trim during multi course voyages. 
         [0016]    Similar sail calculations can be made for non-boom sails (i.e. jib, genoa, spinnaker . . . ) sheets by placing the vectoring load cells on the jib sheet blocks. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
           [0018]      FIG. 1  is a side view of a beam style strain gauge; 
           [0019]      FIG. 2  is a perspective view of the load cell showing the strain gauges mounted on each axis of the rod; 
           [0020]      FIG. 3  is a schematic representation of a Wheatstone bridge for each axis of the load cell; 
           [0021]      FIG. 4  is a representation of the resultant vector and angle for two forces; 
           [0022]      FIG. 5  is a perspective view showing the load cell mounted on the boat and boom sheet attached to it; 
           [0023]      FIG. 6  is a perspective view showing the load cell mounted inverted to the boom and boom sheet attached; 
           [0024]      FIG. 7  is a perspective view showing dual load cells mounted and the boom sheet attached; 
           [0025]      FIG. 8  is a top view representation of the force enacted on the load cell from the jib sail; 
           [0026]      FIG. 9  is a top view representation of the force enacted on the load cell from the sail force; 
           [0027]      FIG. 10  is a top view representation of the calculation of boom angle with known lengths B and C and angle θ from the load cell; 
           [0028]      FIG. 11  is a perspective view of a load cell mounted on a sheet traveler; 
           [0029]      FIG. 12  is a perspective view of the load cell on a traveler offset δ from the centerline; 
           [0030]      FIG. 13  is a top down representation of the optimum angle δ calculated from the known wind angle ω and known boom angle α; 
           [0031]      FIG. 14  is a block diagram of the system; and 
           [0032]      FIG. 15  is an illustrative display layout of the system that could be used in some embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    In the following detailed description of the invention of exemplary embodiments of the invention, reference is made to the accompanying drawings (where like numbers represent like elements), which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, but other embodiments may be utilized and logical, mechanical, electrical, and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
         [0034]    In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it is understood that the invention may be practiced without these specific details. In other instances, well-known structures and techniques known to one of ordinary skill in the art have not been shown in detail in order not to obscure the invention. Referring to the figures, it is possible to see the various major elements constituting the apparatus of the present invention. 
         [0035]    Now referring to  FIG. 1 , the load cell  100  used by the present invention is a cylindrical beam style load cell  100  mounted vertically, either attached to the boom or the deck  102 . The cylindrical load cell  100  is created via a solid bar  103  with strain gauges  104  and  105  on the longitudinal axis, and strain gauges  106  and  107  on the axial (y) and lateral (x) axis with the boat as shown in  FIG. 2 . By placing the strain gauges  104 - 107  along the forward and lateral axis (x), they independently measure the axial (y) and lateral (x) forces. Each axis force is independent and only acts upon that axis. 
         [0036]    A simple circuit such as a Wheatstone bridge  200  shown in  FIG. 3  can be used to read the differential voltage from the strain gauges  104 - 107 . Analog input circuitry can amplify and interpret the differential voltage into a force measurement in the forward and lateral direction for an embedded processor. Using Pythagorean Theorem and basic trigonometry principles as illustrated in  FIG. 4 , the vectored force (A) and the vector angle θ can be calculated from the axial (Ay) and lateral (Ax) forces measured by the strain gauges  104 - 107 . This information can be displayed on a gauge or digital display  1500 , or communicated through a network to other devices or systems on the boat. A display  1500  could visually show the force amount  1505 , vector/direction  1506 , wind speed  1506 , current angle  1504 , optimum angle  1503 , and instructions  1502  on what action should be taken, such as “let out” or “take in” as well as showing a visual representation of the boat, boom, and sail(s). 
         [0037]    Now referring to  FIG. 5 , in one embodiment, the load cell clevis  501  has the sail sheet  502  affixed to one end, and the other end of the sail sheet  502  is attached to a traveler  504 . The sail sheet  502  engages the sail or boom  503  by being attached or strung through one or more loops or points  505  and  506  on the sail or boom  503 . 
         [0038]    For boom mounted sails, the load cell  601  is mounted to the boom  605  and needs to be mounted to one end of the boom sheet  602  and one end on the traveler  604  as shown in  FIG. 6 . The load cell  601  can be mounted on the deck  507  as shown in  FIG. 5 , or inverted on the boom  605  as shown in  FIG. 6 . To provide the widest range of angular measurement, the deck connection point should be mounted forward of the boom mount. 
         [0039]    If multiple sheet blocks are used, two or more load cells  701  and  702  can be used to formulate the force vector. Now referring to  FIG. 7 , two Wheatstone bridge configurations can be used in parallel to electrically produce the resultant force axially and laterally or separate input circuits can be used to calculate the resultant force. 
         [0040]    In another embodiment, when the present invention is used for jibs or genoas, the sheet block(s)  803  and  804  would be mounted to a vertical load cell on both the port and starboard side. The sheet block(s)  803  and  804  can also be hard mounted as shown or mounted to traveler blocks as shown in other figures. Since the jib sheets and genoa sheets  805  are usually used with winches, the resultant vectored force is offset due to the position of the winch  801  and  802  relative to the block(s)  803  and  804  as show in  FIG. 8   
         [0041]    Now referring to  FIG. 9 , the force of the sail  901  is transferred to the boat  900  through the mast mount  902 , stays, and mainsheet. The mainsheet pull is only relative to the total force, but is linearly proportional to the total force since it is not a fixed end. 
         [0042]    As illustrated in  FIG. 10 , the distance from the sheet block  1001  to the mast  1002  is fixed and known as represented by B and the distance from the mast to the boom sheet pin is known and shown as C. Using the cosine law and the calculated angle of the sheet θ, the angle of the boom α can be determined. 
         [0043]    Using the angle of the boom α and the vectored angle of the sheet θ, the relative axial force upon the boat can be calculated. This force is only a fraction of the total force enacted on the boat from the sail; however it is linearly proportional to the total force. 
         [0044]    If the load cell  1101  is mounted to a travel car mounted on a travel rail  1103  affixed to the boat as shown in  FIG. 11 , the angle of the boom a will be offset σ by the traveler car&#39;s distance  1202  from a center position down the longitudinal axis of the boat  1201  as shown in  FIG. 12 . 
         [0045]    As the user pulls in or releases the mainsheet  1203 , the present invention calculates the angle of the boom σ, and if the forward force is increasing or decreasing. If the angle α is growing, and the forward force is growing, the user is instructed to “let out” the sail, or by an arrow indicator on the display  1500  as shown in  FIG. 15 . If the force is decreasing and the angle of the boom is growing the user is instructed to “pull in” the sail. If the force is decreasing and the angle is decreasing, the user is instructed to release the sail. The display arrows  1501  show the direction to release or pull in the sail. The display  1500  may also have a navigation panel  1507  for scrolling through the information being displayed comprised of one or more buttons or controls. 
         [0046]    Each sail type has different properties and performs optimally at different angles ω to the wind. Using separate wind direction sensors along with the calculated boom angle α, the angle of the wind relative to the sail  1300  can be calculated as shown in  FIG. 13 . Each time the optimum force is calculated, the electronic system can learn the optimum angle of the wind relative to that particular sail, and provide feedback to the operator in terms of the best angle at which to set the sail. 
         [0047]    Now referring to  FIG. 14 , a block diagram represents the components of the present invention for one embodiment. The electronic system uses an electronic module  1401  to calculate the “best angle” to control an electric winch  1402  to reel in the sail or un-reel the sail to the best angle to provide the optimum force and provide a visual display  1406  for operators to view. The electronic system could directly activate a relay to the electric winch  1402 , or send a CAN network message to a separate winch control module. Alternatively to adjusting the sail, the electronic system could interface with other network devices  1403  such as an autopilot steering system using NMEA 0183 or 2000 messaging to instruct the autopilot to turn the boat into or away from the apparent wind direction to achieve the best angle of the sail to the wind. 
         [0048]    Using a separate wind speed sensor, the normalized force for angle can be calculated by dividing the calculated sail force as provided by the force sensor  1404  by the effective wind speed as provided by one or more mast mounted anemometers  1405 . This will improve the ability to calculate optimal angles and optimal sail trim by negating the variable wind speed. 
         [0049]    Thus, it is appreciated that the optimum dimensional relationships for the parts of the invention, to include variation in size, materials, shape, form, function, and manner of operation, assembly and use, are deemed readily apparent and obvious to one of ordinary skill in the art, and all equivalent relationships to those illustrated in the drawings and described in the above description are intended to be encompassed by the present invention. 
         [0050]    Furthermore, other areas of art may benefit from this method and adjustments to the design are anticipated. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.