Multi-GRIB routing

Expert

The essentials

Multi-GRIB routing combines several wind files in a single routing: a fine model for the start, a long-range model for the rest.

To start one, tap the small “+” under the “Wind” row of the “Routing” window and choose a second wind GRIB.

Going further

How the app chooses the file

With several wind GRIBs, the app chooses, for each point and each moment of the calculation, the best file that covers that point at that moment, according to three criteria, in this order:

  1. the finest grid (a 0.025° GRIB takes precedence over a 0.25° GRIB);
  2. with equal grids, the most recent run;
  3. with equal runs, the most recently downloaded file.

The models are therefore not blended but chained: when the boat leaves the area or period of the fine model, the calculation switches to the next one. The order of the rows in the window does not matter. Each row has its own wind percentage.

Example: a passage from Lorient to A Coruña with AROME 0.025° for the start and ARPEGE or ICON Europe for the rest, once AROME reaches the end of its forecast range. A single routing replaces two successive routings.

If only the first GRIB seems to be used, it is often because both files cover the same area and the same period: the finer one then wins everywhere. Multi-GRIB is useful when the files complement each other, in area or in duration.

When the routing uses several models, the “Wind Model” column of the routing table shows which one was used for each leg (see Read a routing). A multi-GRIB routing cannot be recalculated with “Recalculate”.

See also