Weather Routing

Weather Routing is the combination of the route required, from point A to point B and any land masses in-between, combined with the weather forecast for the route and your boats performance data. Put all that information together and with the right software and knowledge you can find out the optimum route . If you wondered how the proffesional sailors pick their routes during distance races then this article from Mike Golding and found on his web site lets us in on some secrets.

Below you will see Mikes required route to cape Horn and how he chose the optimum route. Hardware and software; Mike has MaxSea from Furuno, Deckman, and Tactique onboard Gamesa and uses GRIB files from GRIB.

The technology behind Vendée Globe routing

The following article was written by Mike Golding.

For the navigation, performance and weather software which Mike Golding uses onboard Gamesa, the very simple computing maxim holds true: ‘it is the quality of the information put in which directly governs the quality of the output’. Hence, for example, one thing which is fundamental, is the quality and accuracy of the boat’s performance polars (the computed optimum speeds of the boat at different wind strengths and angles) which become the target and the measure of the boat’s performance.

Mike has a variety of weather and routing packages on board, but it those which he has become most familiar with over the years which he continues to favour.

The basic tools are a routing software package MaxSea which is fed weather data from a package delivered by GRIB.US. The weather files are updated every six hours and it is the arrival of these files which dictate a lot of Mike’s routine. He will run new routes when the files arrive, and will compare different weather file sources – basically European or American derived data – and will regularly run the routes of his rivals to see how they compare.

We caught up with Graham Tourell, Mike’s Boat Captain to give more background to the all important routing.

Article at

Describe the technology Mike uses and what has changed since the last edition of the Vendée Globe?

weather routing
weather routing

In terms of the software, Mike has MaxSea, Deckman, and Tactique onboard Gamesa. These programs are all designed for weather routing, performance monitoring and data logging.

For routing, they use GRIB files to calculate the fastest route of the boat from A to B. GRIB stands for Gridded Regularly-Distributed Information in Binary Form and is basically the mathematically accurate data supplied for Numerical Weather Prediction. Most come from NOAA (National Oceanic and Atmospheric Administration) in the USA.

The GRIB files are updated and downloaded every six hours, then loaded into the software for it to work its magic!

A lot of the French sailors run Tactique because it is an all encompassing package which does routing and crossovers. Alternatively there is Expedition which is more tactically based, more akin to Deckman.

All of the skippers will, on a fairly regular basis, plot the routes of their nearest rivals. They will compare them to see how they vary and to see what, if any tactical advantage they may have. This is where experience comes into play: looking for tactical gains.

Using a website GRIB.US the GRIB file forecasts are supplemented with real time satellite images. The great thing about the GRIB.US package is that you can overlay the satellite images over the corresponding GRIB files to see if the files match up. For the arrival and passage of fronts, satellite images are crucial.

I don’t think the technology has changed massively in the last four to eight years. MaxSea Chopper has been around for many years. However, I think the weather forecasting models are getting more accurate and the other thing which is significantly better for all of the boats is that each has a much more accurately developed set of polars, and the polars are pretty critical to successful routing. Today, with the boats being more ’rounded’ in terms of performance, the polars have to accurately reflect the performance profile. Otherwise you will find that you can’t hold on to weather systems for example. One hour can be critical at some stages.

How does the routing work?

The routing software basically takes the boat’s performance polars for any given wind strength and direction and it will compute the fastest course for the boat. You can set the isochrons (which are literally computations of how far the boat will travel in the given wind strength and angle) to study a set wind angle.Or, the example here shows a desired route (the dotted line) which in this case goes to Waypoint 2 which is the next Ice Gate (Pacific West) and Waypoint 3 at Ice Gate (Pacific East) and the last Waypoint at Cape Horn.

Required Route

In this example the isochrons are set to a 60 degrees study: 60 degrees from the centre line of the selected route.

The programme then sequentially breaks the route into two hour ‘bites’ and then builds the optimum route, taking each forecasted wind speed and angle every two hours. If the conditions are changeable, such as when Mike was trapped by the high pressure trough last week, he would have been running shorter route with very short intervals for maximum accuracy.

When you strip the isochrons away then you see your optimum route where every single one of the squares is a two hour interval. Generally, the route is updated every six hours when the new GRIB files are available, so 24 or 48 hours ahead can be drastically different. Mike will save the routes and monitor them day by day, seeing how the patterns develop. Within the MaxSea software, having run a route, there is a section called ‘Route Centre’, which is the optimum route in data form, almost like a diary. The Routing Centre looks like a spreadsheet, an output of the wind direction every two hours, wind speed, expected course sailing angle and the real time ETA to that point. By looking ahead, you are able to see and set up your sail plan accordingly. That is where Tactique is especially useful, mapping out the sail changes ahead. But sometimes skippers don’t follow the routing and it could be because they are keeping an eye on other skippers; they might have a gut feeling or a hunch based on a satellite image showing a small gain, or perhaps are trying to cover a competitor, which may not be the direct route, but tactically is the right thing to do.

Ultimately, even with some of the most advanced technology in the world onboard, it’s down to the skipper to decide, on his own and unassisted, how he sails his boat.

Maxsea Routage Meteo

The Weather Routing is an optional module. To check if you have this add-on, select “About MaxSea” under the MaxSea Menu. The Routing Module would appear listed under “Activated Module”.

The unique Routing algorithm developed by MaxSea uses the isochrons method (displayed on the charts using yellow and purple curves). Each isochron represents a group of points that can be reached in the same amount of time. The calculation of the isochrones take into account the weather forecast (wind, Waves), currents and the boat characteristics. The boat characteristics are factored into the equation from a polar curve diagram (called “Wind Polar”) which relate boat speed to wind speed at a given windangle.

One of the most important factor involved in achieving the optimum course is the weather forecast: make sure to use the most up to date weather forecast available when launching a routing. Another important factor are the polars file loaded in MaxSea. While the default Wave Polar can be use with great result in most of the case, the Wind Polar should be adapted to each sailing boat. At minimum, it is recommended to use a Wind Polar file from a boat of the same category. You can download various Wind Polar files from the maxsea website (Log In to “My MaxSea” and select “Download”).