Routing ships with the currents

Image of the Month - April 2011

A-priori route (in black; in blue shortest route) and route recommendation (in red) overlayed on a current forecast map for March 31, 2010. The a-priori route would have been straight against the northwestward current. Going a little more off the coasts, and at one point (at about 57°W) catching the current around an eddy, enabled to gain about 8% fuel over a Houston (USA) to Santos (Brazil) trip. (Credits CLS)
Kinetic energy from altimetry-derived geostrophic currents (absolute geostrophic currents), and geostrophic currents (white arrows). Such data are assimilated within the models to obtain the left map (along with winds used to compute the total currents). Note, however, that they do not constitute the whole current, since they are computed from the slope of sea surface heights.

Most of the goods transported across the world are loaded on a ship at some point or the other.  So about 3 to 5% of CO2 emissions are due to merchant ships, and, moreover, their fuel is very heavy in sulfur, thus leading to substantial pollution. Several ideas are under study to decrease this (especially with the perspective of an increase in marine shipping in the next decades). One of the ideas that can already be applied is the optimization of the ship paths. Weather routing, i.e. optimization of a ship path following the weather conditions is quite commonplace. But oceanic routing can also be proposed, with the course optimized with respect to the surface currents.

Using ocean models like Mercator, which assimilate altimetry data on an operational basis, best routes are proposed to shipping companies and their captains. Depending on the areas, the conditions and the currents, fuel saving can go up to 8% (on average about 4%). 

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