Historical Grib data is needed for one of the first steps in planning your passage or race leg. Intialy before you get deep into planning your leg you do this historical routing. Software like Expedition and Adrena can do this for you. In the Globe 40 we used the last 10 years of weather data Reanalysis ECMWF weather data for each leg. We used this to generate optimal routing for each year across 10 days. This provides your initial starting when you plan.

Historical Data (You will need to create a free account)

Sailing It all begins and ends with the data.