Sailing weather prediction

Weather routing is a commercial service provided by commercial companies for cargo ships, to optimize their voyage performance. An adventure version of the same used for sailing boats is referred to as Sailing weather prediction or Sailing weather routing. The latter focusses more on the forecasting and routing of wind and currents for adventurers and competitive sailors participating in ocean sports like yacht races.

Weather forecasting for sailing involves several activities such as weather training and coaching, dissemination of data for use in navigation and route planning software, race modeling which involves historical weather and sea state analysis for yacht and sail design, trip and adventure planning for distance races and record attempts, monitoring for departure and trip weather windows. It involves several type of events such as day races, long-distance races, around-the-world-races, and record attempts. It is routinely used in races such as Volvo Ocean Race, America's Cup campaigns, and olympic classes regattas.

A number of large cargo ships use weather routing services for ocean passages. They are primarily geared towards protecting owners and charterers from speed claims, a secondary use being to reduce fuel consumption and improve ETAs (estimated time of arrival). There exist a large number of such ocean weather routing companies, such as WNI, Ocean routes, Storm Geo AWT(formerly Applied Weather technology), WRI and SPOS. Promoters of weather routing companies cite high fuel savings due to their use, while many mariners tend to be sceptic of their advantages due to a large number of maritime accidents (such as the sinking of the Derbyshire, and the parametric rolling of APL China) and cargo damages that continue to occur even when vessels follow routing advice. Most routing programs employ the Dijkstra algorithm and do not consider the different responses of each ship to the same weather, as the latter is difficult to estimate.

Weather forecasting for long distance races is based on dissemination of meteorological data, most often in GRIB format, for use in navigation and route planning software and yacht characteristics (polars), providing guidance, as well as analysis of historical weather and sea state data.

GRIB (GRIdded Binary) is a concise data format commonly used in meteorology to disseminate forecast weather data. For sailing purposes the GRIBs are transmitted and received at sea. These GRIBs contain only small subset of surface data, usually winds (direction and wind speed), information about wave strength (proportional to significant wave height) and direction, surface pressure. The data is further reduced by providing its subset around the position of a yacht. The data is transmitted over satellite phones and single side band radios.

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