New Routing Options
Advantage Level 2 includes a unique routing engine to compute the optimal route from point to point. Like the "isochrone" method used by all other programs, the Advantage router computes the quickest route and shows where the boat could be on different routes at a series of intermediate times. Unlike other programs, Advantage computes quantitative comparison routes, so that you can tell at a glance just how much (or how little) is gained by taking the optimal route. Both comparisons are important, since you may want to deviate from the optimal route to cover a competitor and it is helpful to know how much time may be lost by doing so.
Level 3 adds the following new options, which break further new ground in routing compations.
New Windward/Leeward Routing Option: this provides a more efficient and accurate routing solution for upwind or downwind legs. The new "W/L" button on the routing form below is used to select this option (the "R" button selects the standard method). The "W/L" choice appears when you route upwind or downind with constant wind (for current-based optimal routing), or with a local wind model that is primarily up or downwind. The example below applies this to an upwind leg west of Block Island (assumes wind from SW).
Windward/Leeward Routing. The image below show result of routing, in which the optimal red route approaches the mark along the current-
corrected port layline (magenta dots). As with the standard ("R") method, the black dots show intermediate positions on the optimal and comparison routes, and the "DTG" column shows the "distance to go" (to the destination mark) from the black dot on each route. You can use the "animation" ("A") function to step along the routes at a series of precomputed intermediate times, or enter a time of your choosing.
Minimum and Maximum Wind Option. In an ocean race, routing can be very sensitive to the wind forecast file (wind model) when the optimal route passes close to a region of low wind pressure. The difference between just getting by the "hole" and getting stuck in it can be a relatively small inaccuracy in the forecast, in location or in timing. Level 3 adds a new "minimum wind" option, to specify the minimum acceptable windspeed in the routing. You type a minimum value in the "Wind Min" box and/or a maximum value in the "Wind Max" box. The idea in specifying a maximum value is that beyond a certain point, higher windspeeds do not translate to higher boatspeed (in fact, to the contrary). The max/min function is used in combination with the new option on the routing result form, which shows the minimum and maximum wind encountered at any intermediate point of the optimal and comparison routes (see new Wind Analysis Options). If you see that the optimal route includes points with wind at 2-3 knots, it is worth rerouting with a specified minimum (say 4 knots or more) and comparing the results.
WIND VARIATION ROUTING
Varying Winds in Current-Based Routing. At short distances, for buoy racing in a venue with non-uniform current, one routes with constant wind (typically the wind measured at the moment on boat instruments). Almost always the wind will shift somewhat during the time it takes to complete the leg, so it is of interest to know how the optimal route changes for different assumed wind. The new "Vary Wind by" option on the routing form (above) allows you to perform a different calculation that finds only the optimal route, but for a spread of possible wind directions centered about the assumed wind direction. The first image below shows the standard routing, with optimal and comparison routes.
Varying Winds Computation. Varying the wind in increments of 10 knots about the central value of 250 (used above) gives the result below, consisting of optimal routes for the wind directions in the right-hand column. Here the central (blue) route corresponds to the optimal red route above, while other colors correspond to optimal routes for wind directions ranging from 230 to 270. In this example the optimal route is quite stable for a range of wind directions, except for 230, which is quite different. The "Vary Wind" function allows you to explore this possibility and interpret the "optimal" solution accordingly (something not possible in other programs).
Varying Winds in Wind Model Computation. For longer races, with a wind prediction file, the "Wind Vary" option shifts (rotates) all of the winds predicted in the file by the same angular amount. The first image below is the standard calculation, with optimum and comparisons.
Same calculation as above, with wind rotations. For this wind model the optimal routes all lie within a narrow band because the solutions track maximum windspeed and are fairly insensitive to direction. This is typical when the wind allows reaching angles over most of the course.