Transatlantic: navigation and autonomy

© Maéva Bardy / Fondation Tara Expéditions

14 June 2016

After departing from lorient on may 28, Tara will take  30 days to arrive in miami (Florida) on the east coast of the United States. A flexible route determined by weather conditions and the requirements of scientific research.


Centrale de navigation reliée au GPS, au sondeur et à l’AIS (Automatique Identification System).Navigation unit connected to GPS, sounder and AIS (Automatic Identification System) © Maéva Bardy / Tara Expeditions Foundation


Friday, June 10, our current position is 33°35′ N – 37°31′ W, a point in the middle of the Atlantic Ocean. The “route fond” which indicates the actual progress on the map in relation to the seabed is 195 ° (heading southwest) and we are moving at a speed of 6 knots, or about 11 km/h. The 3 sails – foresail, staysail and mainsail – stretch into the sky. But with the wind at only 16 knots, sails are not enough to move Tara’s 140 tons. One of the motors must be used in order for us to arrive on time in Miami where Tara is expected on June 28th. Still 2,270 nautical miles (4,200 km) to go, along a route that is adjusted each day to find the best way to meet the imperatives of the whole expedition. Contrary to what one might imagine, the major challenge of this crossing is neither food nor water, but fuel: the desalinator is capable of delivering up to 270 litres per hour. As for food, during the Arctic drift 8 tons were stored on board. Clearly Tara’s capacity is more than enough for the 2 tons of food stocked for our Atlantic crossing.


Daniel Cron, chef mécanicien, effectue la première vidange des nouveaux moteurs.Daniel Cron, chief engineer, performs the first oil change of the new engines © Maéva Bardy / Tara Expeditions Foundation


At Lorient, the tanks were filled half-way with 20,000 litres of diesel fuel — enough to navigate for 25 days with both engines at cruising speed. This corresponds in principle to a maximum consumption of 800 litres per day if there’s no wind. “This may sound like a lot, but it’s very little compared to conventional oceanographic vessels. Tara’s strength is her low operating costs and reduced environmental impact,” says Captain Samuel Audrain. This estimate takes into account the production of electricity stored in batteries and used by the navigation instruments and scientific equipment: refrigerator and freezer (where samples are stored), measuring devices running continuously 24 hours per day. For example, the particulate air sampling requires a pump which alone consumes 25 amp-hours of the 240 amp-hours supplied by the batteries. Autonomy is limited to about 2 hours when the boat uses wind power, but this will probably increase because the idea is to introduce more renewable energy.


Nicolas Bin, second, monte au mat avant pour remettre en place les écoutes de la voile (misaine).Nicolas Bin, first mate, climbs the mast to adjust the ropes © Maéva Bardy / Tara Expeditions Foundation


Ideally, the trade winds — blowing continuously from east to west, north of Ecuador, could push us to the coast of the US, but this would mean heading south and lengthening our route with the risk of not finding powerful enough winds. Indeed, in this season winds are not favorable. We must find a compromise to meet the timetable of this 2½ year expedition. The choice of course is based on weather forecasts downloaded daily via satellite. These surveys provide information on changes and anticyclonic storm systems and thus on the strength and direction of the wind. An indispensable tool for the captain to maximize wind power while optimizing the distance. Hopefully Eole will blow a little harder!

Maéva BARDY, correspondent on board


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