10 years ago we developed a technique for constructing accurate, point-by-point current "models" based on actual measurements and local data. Our technique and model predictions were tested against ongoing NOAA measurements of current flow, and we implemented our models with PC software. For the first time, it became possible to predict detailed current patterns in advance of a race and to incorporate local current variations in tactical software. THESE VARIATIONS ARE THE KEY TO OBTAINING A TACTICAL ADVANTAGE: when there are point-to-point current variations, there is a favored route to approach the mark, even in short buoy races where wind is relatively constant.

In 1998 we developed a custom current model for the Solent and English Channel, for Ted Turner to use on Sayonara in the Fastnet Race (see article on our current methodology in Seahorse Magazine I). Since then, we have developed current models for all major U.S. venues and many foreign venues. Our programs have been used by world-famous navigators such as Mark Rudiger, Stan Honey, Marcel van Triest and Jean-Yves Bernot, and by top teams in virtually all major races worldwide, including the Americas Cup, last Whitbread, Volvo Ocean Race, the Fastnet, Sydney to Hobart, Pacific Cup, Transpac, Newport to Bermuda, DCNAC, Pineapple Cup, Farr 40 Worlds, Melges 40 Worlds, Star Worlds, and many others.

After 10 years, our software remains the ONLY software to utilize local current variations for short-range tactics, and the ONLY software to use point-by-point currrents in U.S. waters. But our software was designed for the processing speeds, graphics capability and memory of PC's at that time, and was limited by the electronic charts then available. In the years since, all of these factors have changed dramatically, and we have responded with the development of ADVANTAGE. This new program is designed for use with the latest operating systems (Windows 2000 and XP), and as a result is significantly faster, more stable and easier to install. The interface has been simplified for ease of use, and Advantage incorporates a host of new features and functions not previously available. Plus, Advantage now includes many more (and much more detailed) charts, and superior chart-handling functions that locate the best chart and seamlessly blend adjacent charts to optimize the display.

Our competitors offer only a single computation that can lead to a tactical advantage: "weather routing." The idea is to find a route that takes the least time, taking into account wind and current variations along the way, both point-to-point and over time. However, without a source of local current data, these programs cannot determine an optimal route, and so they are only useful for long (ocean) races, where wind variations are the sole issue. They are also based on a now-antiquated technique, which yields minimal information compared to the corresponding function in Advantage. [For a comparison of our method to the older technique, see below and the second article in Seahorse Magazine II]

At shorter range, or where currents are important, our competitors don't help you. They either ignore current, or use average values which make it impossible to determine the tactical advantage of one sequence of tacks over another. Using averages is equivalent to assuming uniform (unvarying) current, which implies that any sequence of tacks to the mark takes the same time. But when current varies, the optimal sequence can be minutes, sometimes many minutes, faster than another choice of tacks. This is critical information if you want to have the tactical advantage, and only Advantage can supply it. [See discussion of our "Super-If" function, compared to the "What-If" function offered by competitors] In fact, without a proper treatment of current variations, it is impossible to compute a realistic, current-corrected layline, or estimate the time to either layline.

Advantage also offers another unique option, the "Course Solve" function. It applies wind and current data and your boat polars to compute the time to complete a pre-defined course, in addition to current-corrected headings, times and arrival times at each intermediate mark. This differs from a routing solution in that you define a specific route and "Course Solve" determines how long it will take. By defining alternative routes and recomputing, this allows you to compare alternatives of your choosing.


Other programs display currents at isolated points, taken from NOAA publications which are often outdated. There is no way to interpolate between these points, so they are useless from the standpoint of tactical computations. We build computer models which compute current at EVERY POINT, so you can customize the display by adding display points anywhere you like and perform calculations which require continuous, point-by-point coverage.
Current Display Option 1: magnitude plus direction streamer

You can add additional display points anywhere you like (yellow boxes) to add to the default points (blue boxes).

Current Display Option 2: vectors proportional to speed

The program automatically chooses a representative points at which to display a current vector. Zoom in for more detail.

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Other programs have a function that calculates the time to each layline, and total time to the mark, when you input constant wind and current values. This is often called "what-if." But the time to reach the mark is different, depending on which tack you do first, whenever current varies across the course. The Advantage "Super-If" function replicates the "what-if" function when currents are uniform, but also calculates the exact result when currents vary. In that case it identifies the optimal tacking sequence and indicates how much faster it is than the alternative.
The example below shows a boat tacking upwind to Mark 1, just east of the Golden Gate Bridge (approximate position of Blackaller buoy), in a flood current of up to 3.5 knots. The magnitude and direction of current varies significantly in this region. As a result, laylines are generally curved, not straight (the magenta dots indicate the current-corrected layline). The form at the right shows the result of the Super-If function, which compares two alterative routes to the mark: a starboard tack to the lower (port) layline, vs. a port tack to the upper (starboard) layline. The caption of the form indicates that the former alternative is more than 8 MINUTES FASTER, a huge difference in racing when the mark is little more than half a mile away. In addition to total time to the mark, the form indicates TWA, distance, time and heading to each layline. When  using instrument data, this result is automatically recalculated every few seconds, and each time the wind changes.

For comparison, the form also shows average current towards the mark, and from left to right, taken from the current model. This is provided as a guide, in case the user wants to perform a standard "what-if" calculation. To do this you click the 'Enter Data' option box, edit the current and wind values to suit and click 'Calculate.'

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Other programs use an old technique called "isochrones" to compute the optimal (quickest) route to the mark. Our method is unique and provides more information. In addition to computing the quickest route (red route below), the Advantage Router computes a number of alternative routes for comparsion (other colors). These alternatives are defined by a number of criteria in order to contrast with the optimal route, and provide more insight into just how much faster the optimal route is, and whether there are alternatives that are almost as fast. In actual racing conditions, you may want to "cover" a competitor and it is helpful to know how much time you will lose in altering course from the optimal.
The example below shows a downwind approach from west of the Golden Gate against an ebb current. The time is 2 hours after maximum ebb and the current is starting to turn at the edges of the region. There are regions of favorable (flood) current along both the north (Marin) coast and the south (San Francisco) coast which can be exploited to shorten the time. The question is which is quickest, which may depend on the strength and direction of the wind, as well as boat polars. In this case the wind was taken at 10 knots out of 250 deg true (very typical values), for J120 polars. The times for each route are shown in the Best Course Comparisons box, color-coded to match the route (in this case the yellow route coincides with the red). While the northermost (green) route is faster than routes in the middle, the southermost (red) route is more than a minute faster. Even routes which pretty much avoid the middle (blue and black) are 3-4 minutes slower.

The Comparisons form allows you to "step" along the route at time intervals, or pick any time of your choice. The black dots on the various routes show the predicted position of the boat at that time, and the right-hand column shows distance to the mark from that point. The numbers below show that while the red route is ultimately faster, at this intermediate point (at 1511 on 3/28) the boat is further from the mark than on the other routes. If you want to see what the current (or wind, in the more general case) looks like, you can click the yellow "T" option box to have the display automatically reset to that time. The router can utilize standard wind "grib" files for ocean passages, or local wind models built with Advantage.

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The Router considers all possible routes to find the quickest. If you have some idea of how you want to go, or want to compare two or more possibilities, Advantage offers another option. You can pick 'Course Solution' and the program will use boat polars and wind and current data to compute current-corrected headings, distances, transit times and time of arrival at each waypoint, as well as total time and distance. It only takes a few seconds to define a 'Quick Course' by point-and-click, so this method can be used even when time is short (say in the middle of a leg, to compute the difference in time of two alternatives to avoid an obstacle). Course Solution can also be used for cruising, or when under power, to compute how long a transit will take, perhaps at different starting times when tidal currents are a factor. You can define overall boat or wind values, or modify these leg by leg.
The example below takes the boat from point Q1, outside the Golden Gate, along north of the cityfront and then south to Hunter's Point. The result of Course Solution is shown at the right. Option buttons allow you to see the list of waypoints (marks), to save the solution to file or print it out. All solutions are automatically saved under a file name based on the date, so solutions can be recalled and compared later.
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