One of the problems with all the weather data available today is being able to assimilate it in useful form, and then using it to get a feel for what an upcoming passage will be like. We’re not only interested in avoiding bad weather, but in how much fuel we should carry in case we need to power, what sort of sails we’ll be using, and how comfortable (or uncomfortable) the passage is going to be.
The fact that we’ll be “racing” down to the British Virgins adds another layer of complexity. Contestants are allowed to use their engines-but have an hour added to their elapsed time for every hour the engine is run. So you want to be efficient with engine usage.
To help sort all of this out we’ve been using a very exciting passage-planning tool. It is a part of a new suite of software tools which SetSail, ourselves, and some of the SetSail correspondents have been involved in developing, and which will be soon available to the SetSail family. We’ll be talking about how we use these new tools over the next few weeks.
This particular planning tool downloads a special long-range weather forecast in a digital file, which is then displayed on top of a chart of the area we’re planning to traverse. We can scroll through the forecast, checking the weather every three hours if we so desire, for upwards of five days. This is exciting enough, but now comes the really cool part.
The software incorporates a simple file which has BEOWULF’s projected performance in various wind speeds and wind directions. It then takes this data, compares it to the weather forecast, and chooses the fastest course for the boat! As part of the output we get a “route list” showing the position of the boat at each interval, the true wind speed and direction, and the boat speed. Using this “route list” we can quickly see how nice or nasty conditions are going to be, and what sails we’ll need to carry. We’ve been running these routings every morning for the past two weeks, checking on the weather patterns, and how long on passage we’ll be. By the time we are ready to depart from Norfolk, we’ll have a good idea of the weather patterns, and what we’ll need in the way of fuel.
One of the interesting aspects of using this planning tool is that you can have a variety of performance files for the boat. For BEOWULF we have four: a smooth water file, where she should be able to sail at maximum performance, a file which degrades performance as the wind increases due to wave action, and two files which incorporate the use of the engine (one agressively, and the other modestly). It is convenient that these performance files are easy to make.
So let’s check the data for today, October 20th (shown at top). First, it takes two mouse clicks and a minute of connect time to download the weather file. The data is then displayed over a chart of the area between Virginia and the Windward Islands. Two more mouse clicks and a “routing” plan is overlayed on the chart. This data will look confusing to you at first, and later on we’ll explain how to use and interpret it-but for today, check out the red line. That is the fastest course given these conditions. This is drawn using our “motorsailing” performance data.
The next step is to check the route list (shown above left). You can see here the time, position, wind and boat data for each interval. If you peruse the right side of the list you will see conditions are pretty light, and there are a lot of head winds (yuck!). We’ve got the performance file to keep the engine on anytime the winds are light ahead or behind us – which keeps speed at 10.5 to 11.5 knots in these condtions. This routing is calling for about 48 hours of motorsailing – more than we like, but it gets us to Virgin Gorda in just a hair over four days. As we are motorsailing, burning 2.5 gallons or so an hour, this will require something less than 150 gallons of diesel.
Sailing route list.