WO2002059636A2

WO2002059636A2 - Navigation aid

Info

Publication number: WO2002059636A2
Application number: PCT/US2002/003164
Authority: WO
Inventors: Stanley Selig; Anthony Hubbard
Original assignee: UPWIND TECHNOLOGIES
Current assignee: UPWIND TECHNOLOGIES
Priority date: 2001-01-27
Filing date: 2002-01-27
Publication date: 2002-08-01
Anticipated expiration: 2003-07-27
Also published as: WO2002059636A3; AU2002247064A1

Abstract

A GPS receiver is adapted to aid in navigation by providing information related to appropriate tacking of a sailboat or windsurfer by displaying at least the destination mark and indicators (21) and (22) relative to the mark that show when it is appropriate to tack.

Description

NAVIGATION AID

Field of invention

This invention relates generally to a device for use in the guidance and control of a vehicle or means of conveyance and more particularly to a global positioning system (GPS) receiver that is adapted to provide directional guidance or control information, especially for aircraft and boats.

Description of Prior Art

It will be known and understood by those well versed in the art that the skipper of a sailboat trying to reach a destination that is located in a direction from which the wind is coming, the "upwind" direction cannot make progress toward that destination by aiming his boat directly upwind. Rather, to reach a destination that is upwind, a skipper sailing his boat efficiently must turn to the left or the right of the upwind direction to a heading that forms an approximate 45-degree angle between the boats centerline and the upwind direction. After completing this turn to the left or right, the skipper can proceed sailing at this 45-degree angle to the wind until he ascertains that his upwind destination point, called the "upwind mark", the "weather mark" or simply the "mark", lies 90 degrees to his boats centerline; at which time the skipper need only turn his boat through the direction of the wind to the opposite tack; where he will he will find that the boat is heading directly at the mark. A tack that is pointing directly at the mark is referred to as being on the "lay line", the lay line being the last tack that is needed to reach the upwind mark. Rather than take one long tack to reach the lay line, the skipper may choose to take a plurality of shorter tacks to reach the lay line. As long as the wind direction holds constant, the sailing distance required to reach an upwind mark by making a plurality of tacks will be exactly the same as the sailing distance required to reach an upwind mark when only one tack is made, the distance sailed not being affected by the number of tacks utilized. Further, there will be no advantage to choosing a tack which takes a sailboat to the left side or the right side of the of the upwind course first, the total distance sailed by these choices being the same.

However, the above equality of choices holds true only if the wind direction does not shift before the sailboat reaches the upwind mark. If the wind direction shifts to one side of the course during the time a boat is sailing an upwind course, the skipper who chooses to sail his boat to that side of the course will be greatly benefited by the wind shift; and, after encountering the wind shift, he will find that his required sailing distance to the weather mark has been shortened. A skipper who chooses to sail his boat on the opposite tack to the opposite side of the course will find that after the same wind shift, he will have a greater distance to sail to reach the weather mark and that his boat, after the wind shift, has fallen behind the boat that sailed to the side of the course to which the wind shifted. The skipper sailing to the correct side of the course will be able to tell when the wind has shifted to his side because the wind shift will cause the leading edge of the sail to luff or flutter. To refill the sails, the skipper must then turn his boat away from the upwind direction. A wind shift that forces a skipper to turn his boat away from an upwind direction in order to keep the sails full is referred to as a "header". It should be noted that this same shift allows a boat on the opposite tack to turn closer to the upwind direction, without luffing the sails, such a wind shift, referred to as a "lift". A header on one tack thus becomes a lift on the other tack; and, a skipper experiencing a header need only tack to gain the benefit of being able to head closer to the mark on a lifted tack. If the wind direction is oscillating, the skipper who sails his boat to the correct side of the course and receives the benefit of the first wind shift can normally assume that the wind direction will next shift to the far side of the course; and, therefore, he should tack and head to that side of the course. He will thus sail across the course in a lift, the wind will shift to that side of the course causing his boat to be in a header. In a header the skipper would tack onto the opposite tack and find that his boat is again in a lift. The procedure is repeated with each wind shift until the boat reaches the mark, or lay line. Dr Manfred Curry, in his book Yacht Racing and the Aerodynamics of Sails and Racing Tactics, published in 1948 was one of the first to realize the importance of wind shifts and their effect on a sailboats ability to sail upwind. In his book he developed a simple rule, "tack in a header", a rule that is still used by modern sailors.

The "tack in a header" rule was simple in concept but needed refinements to make it more precise. Sometimes, wind direction changes take place so slowly that they go by unnoticed. Reference points such as the shoreline are often used by the skipper to indicate when and in what direction the wind changed. (A wind shift will usually result in a corresponding change the heading of a sailboat because of the tendency of a sail to orient itself at 45 degrees to the wind direction.) However, because a boats relationship to the shoreline constantly changes as a boat progresses upwind even without wind shifts, dependence on the shore line to judge wind shifts often result in less than optimal tacking decisions. Further, in many instances such as in long distance offshore sailing, sailing at night, and sailing in fog, the shoreline may not be visible at all, leaving the skipper with no visual references to judge whether a boat is in a header or a lift. In order to resolve these problems, competitive sailors started using magnetic compasses to keep track of the wind shifts. The compass tracks the boats heading and, thus, indicates changes in the wind direction, but the skipper is required to get close enough to the compass to read the headings, to memorize them and to determine whether those changes meant that the boat is on the favored lifted tack or on the wrong headed tack. Further, a second set of heading numbers is needed on the opposite tack each time the boat tacked.

In an attempt to solve some of the problems with the use of the compass, Thomas McDermott, in his book A Manual of Sailboat Racing, an Encvclopedic Treatise for Small Boat Sailors, developed a system shown in Fig. 1 that placed a pair of reference lines A and B on the deck of the boat, the lines forming a 90-degree angle to each other and forming a 45-degree angle to the centerline to the boat. When sailing on a tack, one line, being 45-degrees too the centerline of the boat, would point into the wind and the other line, being perpendicular to the first line would also be perpendicular to the wind. When a boat tacks, the lines switch roles; the line that before pointed into the wind now becomes perpendicular to the wind and the perpendicular line now becoming the line that points into the wind. Use of these reference lines enable the captain to keep the boat on the tack that forms the shallowest angle to the mark, the tack forming the shallowest angle to the mark being the tack resulting in the highest "velocity made good" to the mark. To use the deck lines, the skipper would sight down the line that pointed into the wind and determine whether the mark was ahead of that line or behind it. If the mark falls behind that line as illustrated in FIG. 2 the boat is in a header in relation to the mark and the skipper should tack his boat. Upon completion of the tack the skipper sights down the new wind line and sees that the mark is now ahead of that line as shown in Fig. 3, the mark falling in the area ahead of the line indicating that the boat is now on a lifted, or correct, tack to the mark. Because the two front segments of the reference line formed a 90 degree arc to each other, the new rule for sailors, when using the deck lines, became: if the mark lies inside the 90-degree arc formed by the front two segments of the deck lines, the boat is on the closest lifted tack to the mark and should not be tacked. If the mark is observed to fall outside the front 90-degree arc due to the boat receiving a header wind shift or due to the boat sailing across the course, the boat is not on the closest tack to the mark and should therefore tack. Upon completion of the tack, the mark will be observed to fall inside the front 90-degree arc and the boat will again be sailing on the closest tack to the mark.

In 1968, Selig modified these deck lines by adding color-coding to the stripes. In the Selig modification, two colored tapes bordered each deck line. The tapes, (usually embossing tape) , one colored red and the other colored green, were placed along each side of the deck line so that the green tape was on the front side of the deck line and the red tape was on the back side of the deck line. Now, all a skipper needed to do was to observe whether the mark was on the red or green side of the deck lines. If the mark was on the green side the boat was on the correct tack. If the mark was on the red side of the deck line, the boat was on the wrong tack and should and should therefore tack. The McDermott deck lines with the Selig color-coding modifications were easy to use and highly effective, enabling even sailors with low experience levels to quickly make accurate choices of tacks in shifting winds.

The Selig modified McDermott deck lines had several drawbacks. In order to use the deck lines, the skipper was required to situate himself behind the lines to sight down them, this causing the skipper to be in a location that might not be optimal for attending to the other sailing functions. Further, to use the deck lines, it was necessary for the skipper to visually extend the lines across the water. This visual extension of the deck lines resulted in inaccuracies due to misjudgment of the skipper and due to the distortion of the lines as the boat healed. The deck lines became useless if the exact location of the upwind mark was not known, or if the mark could not be seen due to poor visibility, long distance, fog, nighttime, or in crowded sailing conditions where the presence of other boats "hide" the mark. Further, the deck lines made no attempt to keep the boat on the tack that formed the shallowest angle to the mean wind. The idea of choosing the tack that forms the shallowest, closest angle to the mean wind direction appeared in 1972 with the publication of U.S. patent 3,678,591 to Selig.

In 1972, the disclosure in the '591 Selig patent greatly enhanced the use of the compass in sailboat racing. The Selig compass and reference bar system (shown in top view in Fig. 4), which became known as the "tactical compass", used two superimposed color-coded systems to give the skipper accurate upwind tacking data. The inner system, a series of red and green arcs placed on the compass card told the skipper instantly which tack was the lifted tack to the mean wind. The outer system, a set of red and green arcs placed on a stationary circular base surrounding the compass, told the skipper which tack was closest, lifted, tack to the mark. The skipper could either sight down the reference bars and determine whether the weather mark was on the red or green side of the reference bars, or the skipper could obtain a compass heading of the weather mark and, referring to the compass below the reference bars, ascertain whether the compass heading lies on the red or green side of the reference bars. The tactical compass worked automatically once it was set. The inner system tacked the boat up the mean wind, green indicating the lifted favored tack to the mean wind, and red indicating the headed, incorrect, tack to the mean wind. The outer reference bars used the same color coding but relied upon the skipper visually sighting down the reference bars to see if the weather mark was on the green or red side. Both the inner system and outer system worked automatically once set; and, if the skipper tacked when the indicators were in the red, he would find the indicators were in the green on the other tack. The Selig patent kept the boat on the closest tack to the mean wind and the closest tack to the weather mark. The use of color-coding indicators allowed a sailor with low experience level to tack correctly in shifting winds. Several Patents related to the idea of the tactical compass followed the Selig patent. Patent 3,824,947 created a method for varying the angle that a boat tacks through so that the angle of the tactical compass could be reset for boats that might tack most efficiently at more or less than the normal 45-degree angle to the wind. Other patents presented ways to better view the card on the compass. What each system lacked was a way of tracking the weather mark. None of patents that came after the Selig patent took advantage of the color-coding red and green arcs. While they provided a means for tacking up the mean wind, they provided no means for keeping on the closest tack to the mark.

US 3,804,057 " Sailboat Racing Calculator" discloses overlays, including adjustable arms, for a magnetic compass to assist in calculating appropriate tacks.

US 4, 149,410 "Adjustable Wind Direction Devices" discloses a scale for use with a magnetic compass that provides identical readings with respect to wind direction on both port and starboard tacks.

US 4,481,810 "Adjustable Wind Direction Devices" discloses an adjustable device that, when set while a boat is headed into the wind, indicates to a sailor suitable port and starboard tacking locations by means of symmetrical color coding.

US 4,616,423 "Tactical dinghy compass" discloses a color coded card for use with a magnetic compass.

The Selig invention described in the '591 patent, however, had its own drawbacks. If the skipper wanted to sight down the reference lines or bars he might have to move from his regular seating position. Further, because the mark's position relative to the sighting bars changed constantly as the boat moved across the course, the skipper, in order to take maximum advantage of the wind shifts, would have to make frequent sightings, the time needed to make these sightings being diverted away from other sailing functions. Further, small sailboats sailing in heavy wind required the skipper station himself out to one side to keep the boat sailing upright. From this position, reading the compass was difficult and sighting down the reference bars was impossible. All of the tactical compasses that indicated correct tack based on the mean wind had to be set up by the skipper before the start of the race. Further, each had to be readjusted if it were later determined that the initial reading of the main wind direction was incorrect. The tactical compass inventions, including the Selig' s offered no easy way to make this adjustment. The reference arcs were placed on some arbitrary portion of the compass card, that position of the reference arcs having nothing to do with the compass heading of the boat; this greatly confusing the sailor and leading sailor to improper use and mistrust of system.

There is a need among sailors for a navigational aid that overcomes these problems. There is a need for a navigational aid for use by sailors that automatically adjusts for changes in the mean wind direction.

There is a need for a navigational aid that can advise a sailor concerning the position of a way point, of changes in the mean wind direction and of the boat's position relative to each of them when visibility is less than optimal.

There is a need for such a navigational aid that can be used by a sailor or crew member who is remote from the device or who finds it inconvenient to study an instrument.

There is also a need for a navigational aid that can identify the location of remote objects, such as waypoints and race starting lines while some distance away.

There is also a need among sailors, pilots, hikers and others interested in the efficient movement of vehicles and people from point to point for a navigational aid that can plot and display a greater circle path, that ban identify other vehicles or travelers, that can provide useful terrain or weather information and that can advise a traveler such as a pilot or sailor of course corrections necessary to maintain the greater circle course in the face of changes in wind directions.

There is also a need for a navigational aid that could provide tactical information about the distance, speed, and direction of other moving vehicles or travelers.

Summary of the Invention

It is an object of the present invention to provide a navigational aid that overcomes the problems of the prior art. It is also an object of the present invention to meet the needs set out above.

These and other objects are met by the present invention which, in its simplest embodiment is a navigation aid that includes a GPS having a screen adapted and programmed to show the sailboat on which it is positioned, the destination mark and a tacking indicator. The tacking indicator may be colored or shaded portions of the GPS screen arranged so as to indicate that the skipper should tack when the icon representing the destination mark moves into or approaches such a portion. In another embodiment the invention includes a navigation aid for determining appropriate tracking changes to be made by a sailboat when sailing to a selected destination, the aid including a programmable global positioning system (GPS) receiver capable of determining the location of the boat as it moves and in which the selected destination is programmed and in which a virtual source of wind at the time of sailing is programmed and at least one indicator to provide information based on relative changes in the location of the boat with respect to the selected destination and with respect to apparent changes, if any, in the position of the virtual wind source, upon which information the boat can be caused to make an appropriate tack and wherein the distance from the boat to the selected destination is less than the distance from the boat to the virtual wind source.

In another embodiment, the invention includes a GPS programmed to show a mean wind and a way point and wherein the GPS is also programmed to show changes in the mean wind direction by tracking and making use of recent tacking maneuvers.

In some embodiments the invention further includes indicators to advise concerning appropriate times to tack a sailboat. The indicators may include colored areas on a GPS screen, audible signals, visible signals such as colored lights or colored displays in glasses or binoculars remote from the GPS, or in repeaters driven by the GPS such as wrist watches and the like.

In still other embodiments, the invention may include displays or other signals relating to the location of other craft or to weather events received from broadcasts or from transponders, or the like.

In another embodiment the invention includes a navigational aid for plotting a greater circle course.

In yet another embodiment the invention includes a navigational aid for setting remote way points in a GPS and for determining the speed, direction and location of remote moving objects.

In still another embodiment the invention includes a navigational aid adapted to advise a sailor taking into account factors including water current.

Brief Description of the Drawings Fig. 1 shows a prior art solution including deck lines. Fig. 2 illustrates a boat in a header relative to the mark. Fig. 3 illustrates a boat with respect to a mark both before and after tacking.

Fig. 4 illustrates a prior art device.

Fig. 5 illustrates an embodiment of the present invention. Fig. 6_illustrates an alternative embodiment of a display screen. Fig. 7 shows a software flow diagram related to the use of the invention.

Detailed Description The present includes a GPS receiver. There are many GPS receivers commercially available which are capable of use in the present invention. In one embodiment of the present invention the GPS receiver is adapted to support or to display colored areas on its screen to advise a sailor concerning the need to tack. The colored areas are usually a 90 degree arc generally formed by a "V" shape having a first color indicator in the center of the "V" and second colored areas to the left and right of the "V". The colors may be shadings of the same color but are usually green in the center of the "V" or in portions of the center and red in all or part of the area to the left and right of the "V". When activated, the GPS displays a map-like image of the area around the sailboat, including the way marks.

In operation, the skipper observes the GPS screen and keeps the icon representing the destination mark in the center of the "V" . If the icon for the destination mark appears to move into an area outside the "V" , the skipper knows to tack.

In a more complex embodiment the GPS, when activated, displays on its screen at least an icon for the boat, an icon for the destination mark and the mean wind direction. The mean wind direction is calculated by a sub-program in the GPS based on the tendency of a sailboat to position itself about 45 degrees to the mean wind direction. If the weather mark is already entered into the GPS, it does not need to be reentered and will appear correctly when the GPS is activated. The mean wind line automatically appears on the screen as the GPS is turned on, avoiding the need for a skipper to enter it by hand. While tacking, even before the start of a race or trip, the computer averages the direction of the wind the boat is sailing in and shows faint lines on the moving screen at set time intervals. This averaging is continually transferred to the mean wind line. As lines are entered on the screen they give a quick indication of most encountered directions and the extreme shifts can also be shown. Alternatively, the GPS computer can be programmed to show a "new" mean wind line at predetermined intervals without making its background work visible. Normally, a skipper can override a mean wind indication with a left/ right rocker switch if so desired.

The skipper can read the GPS from any position on the boat, even while "hiked out". In alternative embodiments audible alarms and synthesized or pre-recorded verbal signals allow the skipper to take advantage of the inventions tactical functions without being within sight of the GPS. The skipper can use the functions of invention even when he is hiked over the side of the boat or while he is holding the booms of a windsurfer. The navigation aid can be adapted to broadcast generated by the GPS to a repeater such as a watch or glasses or an ear piece receiver worn by the sailor or by another crew member. The remote device can also receive information through a data cord linking it to the GPS with the wrist device. Signals advising when to tack or to take other action that may be received without removing a windsurfer's hands from his equipment are especially valuable.

FIG. 5 shows a typical global positioning system receiver 1 with view screen 2. A transparent overlay 3 has been placed over the screen. In this example the overlay has an adhesive backing to enable it to be removeably attached to view screen 2. This overlay has a green arc 4 placed at the top or front of the screen. In this example arc 4 is a 90 degree arc. It will be understood by sailors that the 90 degree arc is suitable for the typical sailor who prefers to sail at a 45 degree angle to the wind. The arc can be different for sailors who prefer to sail closer to the wind. The 90 degree arc shown in FIG. 5 is not intended to be limiting, as arcs of a different size can also be used. Lines 5 and 6, which form the edges of arc 4, are, in this example, 45 degrees from the centerline of the screen (not shown). For a sailor who prefers to sail closer to the wind on a tacking course, the angles from the centerline defined by lines 5 and 6 would be different. Icon 7 at the bottom of the screen represents the current position of a sailboat.

Arc 4 is color coded for convenient use. It does not need to be green. The area outside arc 4 in the preferred embodiment is red. This is also a convenience. It could be any color or clear.

In another preferred embodiment, arc 4, is not an overlay but is generated on display 2 by the global positioning system receiver.

Icon 8 represents the selected destination and has been programmed into the global positioning system receiver by the user according to procedures well known by those acquainted with the use of global positioning system receivers. Typically, such programming involves pressing a "remember this spot" button on the receiver while at the location.

Line 9 indicates a way point that represents a virtual wind source that is further from the sailboat that is the selected destination. In the example shown in FIG. 5 the sailor has selected a way point on the global positioning system receiver's compass rose 800 miles distant from the sailboat while the selected destination is about 1 mile distant from the sailboat. The distance selected for the way point representing the virtual wind source can be any distance that results in a smaller angle between a first position of the sailboat and a second position of the sailboat than does the selected destination for the same first and second positions, when the angles are measured at the virtual wind source and at the selected destination. A preferred distance for the virtual wind source point is one that is sufficiently far to produce such an angle that is substantially negligible when compared with the angle corresponding such angle at the selected destination; however, a distance that produces any significantly smaller angle is useful. As discussed above, the line that in FIG. 5 shows the virtual wind source could, in another embodiment, shows the calculated mean wind line.

FIG. 5 also shows extensions of lines 5 and 6 through icon 7 to form a corresponding arc "behind" the icon. This extension is optional. The extension can be substituted for a polar map tailored for the particular sailboat or can include both the extension show in FIG. 5 and a polar map.

FIG. 5 also shows arrow 10 surrounded by color coded fields 11 and 12. As with arc 4, fields 11 and 12 may be coded in any color. In this embodiment, field 11 is green and field 12 is red. Arrow 10 can be used alone or with the other images shown on the screen. FIG. 5 also shows speed and distance display area 13. This display is usual to global positioning system receivers and is not necessary to the operation of the navigation aid. However, many sailors will find it useful to keep display area 13 in view. In one embodiment, not shown, the display includes numerical indices on display

2 that, when intersected by line 9, can be used as factors for the speed of the boat shown by the global positioning system receiver to calculate the velocity made good of the boat with respect to the selected destination. In yet another embodiment, the global positioning system receiver can be programmed to display the resulting calculation. The operation of the invention will be described first in connection with the embodiment of FIG. 5. It is to be understood that the operation may have apparent differences when using embodiments in which the indicator provides information as an alarm or other signal.

In operation, the sailor programs the global positioning system receiver to display a pre-programmed destination and to display a line to a distant virtual wind source. The sailor then sets his sailboat at an angle to the wind and observes the position of icon 8 and line 9 with respect to arc 4. If both icon 8 and line 9 are between lines 5 and 6, the sailor knows the sailboat is on a correct tack to the selected destination.

Icon 8 will move across arc 4 as the sailboat moves on a particular tack with respect to selected destination icon 8. When icon 8 crosses either line 5 or 6 to lie outside arc 4, the sailor can change tack to port or starboard as appropriate. If line 9 crosses either line 5 or 6, the sailor knows that a wind shift has occurred and can compensate for the wind shift by tacking.

Sailors of ordinary skill are familiar with the problems caused by wind shifts. Most sailboats travel about 45 degrees to the wind when sailing upwind. If the wind shifts during a particular tack, the sailboat will usually make a corresponding shift in direction due to a natural tendency to keep about a 45 degree angle to the wind. A sailor may not notice the wind shift and may not adjust for it, causing his next tack to be late or early so as to lengthen his overall distance and time to the selected destination. The selection of a virtual mean wind source that is a greater distance from the boat than is the selected destination will cause line 9 to cross lines 5 or 6 as a result of such a wind shift, providing the sailor information upon which to act to maintain a better course to the selected destination.

Also shown in FIG. 5 are icons 14 and 15 representing other sailboats. It is within the scope of this invention that the global positioning system receiver can receive information about the locations of other craft obtained by means of transponders, directional radio signals, and the like that result in icons such as 14 and 15 to show their position with respect to icon 7, the sailboat operating the invention. As a safety feature, a sailor will know to be alert for boats located at certain positions with respect to his own sailboat. As a racing feature, a sailor will know that he is ahead of or behind certain boats on the screen, as is well known in sailing. These features will be of great advantage when sailing at night or in weather when visibility is reduced. Icons of weather events (not shown) can also be received by the global positioning system receiver and displayed as information useful to a sailor.

A reach or downwind selected destination can be set after a sailboat on an Olympic racing course has rounded the weather mark. The embodiment shown in Fig. 5 is used in substantially the same way going downwind except that arc 16 will indicate information about wind shifts while arc 4 will continue to provide information about the new selected destination.

In still another preferred embodiment, a polar map appropriate for the particular sailboat is generated or overlaid on the display during a downwind leg of a race to provide further information as to appropriate course changes. Fig. 6 shows another embodiment of the invention in which arrows 21 and 22 are generated by the global positioning system receiver so that one represents the direction of the virtual wind source, as described above, and the other represents the direction to the selected destination, as also described above. Field 23 is color coded to indicate information that can be used by the sailor to determine appropriate tacks or other course changes with respect to the destination or with respect to wind shifts, as described above. A sailor can sail an appropriate course to a selected destination and avoid the problems caused by wind shifts, as described above, by simply keeping both arrows pointing to a specific color coded portion of the field.

Fig. 7 shows a flow chart for a software program that would control the images or other indicators providing information to a sailor using the embodiment shown in Fig. 5. In a situation in which a headwind is blowing perpendicular to the starting line of a sailboat race, boats starting at either end of the line will be equal to each other in the sailing distance required to reach an upwind destination. However, if the wind direction moves to one side of the line or to the other, a boat that starts at the side of the starting line closer to the new or shifted wind direction will, in effect, start ahead of a boat starting at the opposite end of the starting line because it will need less sailing distance to reach the mark. Various techniques have been devised to ascertain which end is favored by the direction of the wind. These sailing techniques involve sailing in the vicinity of the starting line and determining which end of the line is closer to the direction from which the wind is blowing. However, the area near the starting line is usually crowded with other boats, which are also trying to determine the correct end to start at. The present invention allows the skipper to place the starting line on the background map. Once the starting line shows up on the screen, a sub-program in the GPS uses the mean wind direction, already calculated as discussed above, to calculate the favored end of the starting line. The GPS is programmed to indicate the preferred end of the starting line by means of a color, an arrow, or the like. Thus, the skipper can carry around an accurate representation of the starting line on his GPS screen as it relates to his craft. He needs only glance down at the screen and ascertain which end of the line is favored. The GPS may also be programmed to calculate from the mean wind direction and from the boat's speed and direction, obtained by normal GPS functions, the time to the starting line for the boat. In one embodiment of the invention countdown timers show how much time is left before the start of the race, how much time it will take to reach the starting line or whether the boat, at its current speed, will be too early or too late to the starting line and by how much.

Embodiments of the invention may also include a position finding device to enter the location of remote points, such as a "mark" or the ends of a starting line in a GPS. A commercially available citing device that includes a compass is connected to the GPS and is used to make a sighting to, for example, one end of the starting line. The sighting is entered into the GPS database. After sailing a distance a second sighting of the same end of the starting line is entered, and the GPS uses a sub-program to calculate the location of the mark using the known distance and direction the boat moves between sightings as one leg of a triangle and the intersection of the two sightings as the opposite angle. The same routine is applied to the other end of the starting line, and the computer in the GPS defines and displays a line between them. This embodiment of the invention can also be used to mark "way" points and to enter them into the GPS display.

In some applications, the navigation aid is electrically or mechanically adapted to communicate with a craft's steering mechanism so that the tacking is done automatically.

The navigation aid of the present invention will also have military applications. In military applications the sighting device has a declination reading so that the angle of inclination can recorded. Thus, two observers operating two units simultaneously could get an exact fix on an aircraft. By taking a second pair of sightings, the speed and direction of the aircraft can be calculated. Use of radar to find this same information will allow the plane to identify the location of the source of the radar and allow an enemy aircraft to return fire. Using this feature to ascertain the altitude speed and direction of flight does not give the aircraft any indicator that it had been located. The system could be used to obtain exact location of other ships or to obtain the location of enemy tanks, artillery and other such targets.

Most commercially available GPS receivers feature a flat rectangular screen with a rotating background map, the map being generated electronically from the data stored in the GPS memory. When a globe shaped map is stretched out onto a flat surface, the latitude lines are spread apart and the image becomes distorted. To compound the problem, courses and route lines put onto the map are represented as straight lines when in fact they would be curved on a globe. These distorted lines do not represent a greater circle or a segment of a greater circle and thus do not represent the shortest distance between points that they connect. When the GPS user operates the zoom feature to bring a small area of the map close in, the distortions have little effect; but when the user zooms out so that the part of the map shown is a large area, the distortions become vary large. These distortions not only cause the user to travel a greater distance to arrive at a point, but they cause lines used as reference bars to give inaccurate tactical advice. In one embodiment the present invention includes a program for calculating and displaying a greater circle route between any two points on the globe and will use greater circles to represent the heading of the boat, the opposite tack course, and the direction of the mean wind even over short distances.

Current GPS receivers rely upon a calculated compass heading to indicate the direction the GPS is traveling and indicate the direction or azimuth to other points on the map. Using magnetic or true north headings creates many problems. For example, a plane flying to, for example, Moscow, Russia, from New York City in the US and staying on the greater circle route would be required to fly in the vicinity of North Pole. As the plane nears the North Pole, the pilot would find that he would have to rapidly and continuously change the heading that would be required to keep on a greater circle. After passing the North Pole the pilot would find that his heading had shifted from roughly north to roughly south. Thus, a plane flying at a constant heading of northeast would fly in a spiral that wound end up at the North Pole while a plane maintaining a greater circle route that headed north east would end up half way around the world crossing the equator heading southeast.

In this embodiment of the invention a plurality of waypoints is placed on the screen of the GPS in such a way that they form a compass rose. The radius of the compass rose is one quarter of the circumference of the Earth. The center of the compass rose is the boat icon on the map screen. When the compass rose screen is activated, the map zooms out to a scale that is large enough to include all of the waypoints. The rose can be zoomed in and out to a size that causes one of the waypoints to land on a desired destination. The waypoints may be numbered the same as compass headings. The waypoint over the desired destination is entered and a line appears from the boat or plane icon, the line leading to the desired destination. This line represents a plurality of points equidistant from the icon that is 90-degrees to the selected icon. These points will, upon examination, be found to 'determine a greater circle segment connecting the GPS location to desired destination. The GPS then gives the operator the heading to start, modifies that heading to keep the user equidistant from the 90-degree point, and thus keeps the operator on the greater circle.

Alternatively, and by way of illustration, the greater circle can be generated between any two points on a globe by using a set of dividers having legs curved so that they can lie flat when placed on a globe. The length of each leg is one quarter the circumference of the globe. When the free ends of the compass are placed on any two points of the globe and the free ends slide together, the resulting plurality of points determines a greater circle segment connecting those two points. To use this feature to draw greater circle routs on the screen of a GPS, first the computer, by algebraic calculation draws two circles, one around the starting point and one around the destination, the radius of which is equal to one quarter of the Earth's circumference. These two greater circles, once drawn, intersect each other at two points. The GPS locates these two points by algebraic calculation. Next the GPS computer generates a second circle one quarter the circumference of the Earth in diameter and having as its center one of the intersections of the first two circles. This last greater circle or two greater circles will pass through the original two points and appear on the GPS screen as an accurate greater circle rout between those two points. The angle of divergence of the greater circle from longitude lines will give the operator the heading he needs to stay on the greater circle. The GPS will inform the operator what direction to take at any one instant to keep him exactly one quarter of the Earth's circumference from the "divider pivot point".

Previous procedures and inventions for determining the correct tack do not take into consideration whether those tacks might result in a boat running into a thunderstorm, running aground or running into other boats. Charts of the bottom only show the bottom on a flat surface, forcing the operator to read the contours of the botto then turn them around in his head to relate them to the boat direction. Airplane pilots are faced with the same problem of looking at a flat map and trying to picture what that flat map looks like in vertical relief ahead of the airplane. A hiker in the woods might have difficulty looking at a thunderstorm on a GPS screen and determining how severe it is because he has no way of knowing haw tall the storm is. A radar scanner projects a slice through a thunderstorm and does not give any indication of the storm's vertical extent. A plane has no way of showing its vertical flight path or how that path may relate to other air traffic, thunderstorms ahead of the airplane, or mountains under the aircraft. In one embodiment of the present invention a vertical screen aligned with the direction of travel solves these problems. Broadcast information about thunderstorms is displayed on the vertical screen. Warning buzzers may be adapted to sound if thunderstorms above a certain level are near a hiker, a boater, and pilot flying an airplane. Buzzers also may be adapted to warn a pilot of possible collision with the ground, and warn the boater that his path may cause him to run aground. The navigation aid may also use stored topographical maps to calculate the location of the vehicle or traveler with respect to surfaces, including underwater surfaces. This vertical display and associated alarms may also make use of information received from broadcast systems or from transponders on other craft. Also, the navigation aid can make use of broadcast changes in the mean wind direction along an extended course to adjust the displayed mean wind direction. It will be understood by those skilled in the art of sailing that the GPS can be adapted to include a factor for current in its calculations.

In one embodiment, a set of color-coded green and red arcs is provided at the bottom of the screen to indicate which tack forms the shallowest angle to the downwind mark. The mean wind line automatically shifts red or green keeping the skipper on the closest downwind tack to the mean wind. A polar diagram is locked to the direction that the boat is heading. A second set of green and red arcs spread to the down wind tacking angle appears at the top of the screen indicating the closest downwind tack to the mark. The mean wind line moves back and forth across the set of green and red arcs and the bottom of the page indicating the closest down wind tack to the mean wind.

In a preferred embodiment for use in sailing, GPS display can be modified to have only two arrows that point to two waypoints at the same time. One arrow points to the mean wind and the other points to the destination. In another embodiment a second set of arrows serve as a guide for downwind tacking.

After reading this description of the invention, it will be apparent that the invention may have many useful embodiments, all of which are intended to be within the scope of the appended claims.

Claims

Claims:

1. A navigation aid for use in sailboats sailing toward a destination comprising a GPS receiver adapted to display a mark for the destination on a screen along with an indicator that can be used by a sailboat skipper to determine appropriate tacking events.

2. A navigation aid according to claim 1 wherein the indicator is a color-coded pattern displayed or overlaid on the GPS screen.

3. A navigation aid according to claim 1 wherein the GPS receiver is further adapted to display a calculated mean wind direction or a virtual mean wind source or both.

4. A navigation aid according to claim 3 wherein the GPS receiver is further adapted to provide audible signals or visual signals for use by the skipper in navigating the boat.

5. A navigation aid according to claim 4 wherein the signals are provided to remote devices.

6. A navigation aid according to claim 5 wherein the devices include lights, synthesized or recorded voices, wrist worn repeating screens, bells and buzzers.

7. A navigation aid according to claim 1 wherein the GPS is adapted to receive and display remote broadcast signals relating to weather or traffic or transponder signals from boats.

8. A navigation aid according to claim 1 further adapted to receive signals from a directional location marker and to calculate the location of remote points based on input from the marker.

9. A navigation aid according to claim 1 adapted to provide signals directly to a motive means for controlling a craft.

10. A navigation aid according to claim 1 adapted to display greater circle courses between points.