Faster and safer

Weather routeing can make a huge different to passage times and race results. Rupert Holmes reports on the tech to help you make good decisions

- Rupert Holmes

The ability to download weather data and run routeing software to optimise long-distance routeing is becoming increasingly accessible, powerful and affordable. It’s no longer the preserve of the best-funded race teams or the largest cruising yachts.

For those whose voyage start dates aren’t decided years in advance by a racing programme or rally timetable, weather routeing software also includes a useful departure date function. This can be used to figure out the best day on which to leave port at the start of a longer passage, to minimise the risk of headwinds, calms, fog or gales. This makes for a very powerful combination that can transform the experience of passage making, leading to trips that are faster, safer and more comfortable. It applies just as much to a Channel crossing, where intelligent use of routeing has the potential to slice a couple of hours off crossing times, as to longer voyages, such as to Ireland, across Biscay or across an ocean.

Data sources

Windy’s excellent web platform and apps have introduced many more sailors to a wider range of weather models over the past couple of years. It’s always worth comparing data from different sources where possible – a high level of agreement shows a forecast in which you can have a lot of confidence. On the other hand, a lack of correlation indicates greater uncertainty, which can also be useful knowledge for decision making.

It’s important to have an appreciation of the intrinsic differences between some of the models. Global models, such as the ECMWF (9km grid size) and GFS (22km grid), give a good ‘big picture’ analysis of what’s expected to happen over a period of several days. However, they lack the finer-grained data that’s needed to make more accurate predictions in the shorter term.