LOCATION: 200 miles E of Barbados
WINDSPEED: 18.5 kts
BOATSPEED: 21.6 kts
DISTANCE TO FINISH: 1,500 miles
Our daily routines are predictable enough. Each day is more or less the same and at some point day 17 begins to feel like day 12, which very much felt like day 6. One variable of inconsistent kind though, and one of great interest to everyone onboard, is Tom’s ETA, or estimated finishing date. Our predicted arrival is something we all want to know and for a variety of reasons, but it’s a figure that is also in continuous flux.
It can be amazingly difficult to predict when you’re going to arrive at a destination 3,000 miles away in a landscape of geographic uncertainty, but today’s software, weather files, and boat performance profiles combine to give it an honest try. There are family flights to book, boat repairs to schedule, food and fuel to manage, and the high hopes of the 11 of us waiting for a burger, beer, and a proper shower, and they all hinge on a very simple process.
Somewhere in the world somebody begins by analysing the weather. Their findings are digitized into “grib” models, a virtual record of predicted winds spanning up to several weeks out for the entire globe. These files are loaded into the onboard routing software that use our current location and our boat’s performance polars (tables that suggest what speeds Mar Mostro should attain at any combination of wind speed and wind angle) to best map our course to the next waypoint.
Obviously, there is more than one way to decipher the weather, so there are multiple models to choose from. With each update (several times a day) Tom downloads either the “EC,” (short for…ECWF), or the “GFS,” (…God Forged Scheduling?), loads it into the software, and out comes an ETA. Routing doesn’t take certain things into consideration, things like a rough sea state that would prevent us from reaching our predicted polar speeds, so there’s a certain degree of human interpretation for Tom before he decides on a route and a date, but eventually a day is picked. The closer we get, the more accurate the prediction power is, but one thing that’s for sure is that we can never be sure.
In the context of this leg, it looks like we’ll be one or two days late, so it’s time to start squirreling away some food again, just like we did on the last leg. Extra bars for lunch instead of a meal when the wind is light, split the chicken tikka – a notoriously large serving – into two meals, things like that. It’s not the models’ fault, or the forecasters that make them, because weather is weather and it changes. You can’t suggest that conditions are “supposed” to be anything, because they’re unpredictable by nature. All we can do is hope the models are more accurate than not!
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