In Expert mode, you have the possibility to adjust the routing calculation parameters. Here are some guidelines on how to do this best. Note that you always have the possibility to reset the default values by pressing the "Reset routing parameters to default" button under the settings. We recommend using these defaults in the vast majority of cases.
Max duration (15 days)
This is the maximum duration of the routing. One may want to reduce it to understand when a route decision should be made. This can be seen during the routing calculation when the best route switches. For example, if we are sailing on the North Atlantic from Brittany to the West Indies. We can have a routing that switches from a northern route to a southern trade winds one in the middle. We calculate a routing with a 15 day max and another one with a 8 day max. We then analyse the 2 proposed routes. If the routes over the first few days are similar, there is no decision to be made immediately. If they are different from the beginning, you have to choose right away.
Sweep angle (40°- 360°)
This is the scan angle over which the algorithm will search for routes. The larger the angle, the longer the calculations, but the less chance you have of missing the best route.
As a general rule, 220° is more than enough. If we notice that our routing passes by the edge of an isochron (locations reachable in a certain time, drawn in blue), we must increase this angle. This happens most often in areas of light wind or for very fast boats like Ultims which can lengthen their route considerably to find favorable winds.
Step angle (Auto / 0°- 5° )
This is the angular increment used in the routing calculations. The smaller it is, the more accurate the calculations are, but the longer the calculation time. In auto mode, it is initially at its minimum of 1°. The router can increase it if the processor is slow and the calculations take too long.
VMG max tolerance (0° - 20°)
The VMG (Velocity Made good) is the speed the boat towards or from the direction of the wind. The best VMG angle is the angle for which this VMG is maximum. In general, it is around 40° to 45° upwind and 140° to 150° downwind. When you are offshore, far from the coast, you rarely sail beyond the angle of best VMG. For us, this can be considered very rarely as never. On the other hand, when you are close to a coast, to avoid making two tacks or two gybes in order to clear a cape, you can sail a few degrees beyond the angle of best VMG. This will avoid 2 penalties and a loss of energy. To conclude, we always do a first routing with a tolerance of 0° and we only put a tolerance higher than 0° to avoid 2 manoeuvres when clearing a cape.
Isochronous < 2, 6, 12, 24, 48, 120 hours
This is the time step between 2 isochrons. This time step increases as you move further out in time because the weather conditions will change by then and it is useless to look for too much precision. Near the coast, it can be interesting to decrease the time step of the first isochrones to stick to the coast. The shorter the time step, the longer the calculations.
Have fun changing these parameters to get the best routing. Remember that we spent a lot of time optimizing the default values. These are the best in the vast majority of cases. When in doubt, don't hesitate to press the "Reset routing parameters to default" button.