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Wednesday, November 4, 2020 

Finnish company NAPA Shipping Solutions has analysed over a year of past transatlantic voyage data for MR tankers, looking at actual performance against performance optimised using weather routing.

To avoid being influenced by hindsight, the retro-optimisation studies only used data that was available at the time of sailing.

In voyage optimisation, NAPA first looks at the speed profile. The captain must plan the voyage accounting for the uncertainty of the weather conditions the vessel will face. Thus, to avoid missing the ETA, vessels often sail faster at the beginning of a voyage and then slow down, which is very inefficient (fuel consumption has an exponential relationship to speed – so it uses a lot more fuel than maintaining the same speed). However, sometimes the requested arrival time changes during the voyage, which is unknown at the time of voyage planning. Thus, voyages with significant ETA changes during the voyage were excluded. The same times of departures and arrivals were used; when optimising the voyages, the arrival time was used as the ETA from the beginning of the voyage, leading to a more even speed profile. Voyage optimisation helps in predicting the arrival time accurately, which gives crew confidence that they will be able to meet the target ETA. This enables the crew to better take advantage of a balanced speed profile.

The second factor, and most important in this comparison, is the route taken. Most vessels tend to take a default route, except in extreme weather conditions, which is simpler from a planning perspective, but misses the benefits of an optimised route. While some climatology based reference routes already exist and could be used for different times of the year, the weather phenomena are so different year-to-year that voyage specific optimisation is needed. For the first day of the voyage, NAPA used only the weather forecast data available at that time, repeating similarly on the following days, so only data available to the crew and optimisation team at the time was used.

After optimisation, both the optimised and actual routes are evaluated using the same hindcast weather information. Based on the comparison, the tankers studied could have reduced the time spent in winds above BF4 by 9.8%, allowing 5% lower RPM and leading to 15.9% lower fuel costs. The study assumed precisely the same schedule as was sailed in reality.

Kimmo Laaksonen, Director, Product Development, said: "The savings would have directly increased profitability. If fuel costs were 50% of the total voyage cost, the savings would have resulted in nearly 8% higher TCE (Time Charter Equivalent)."

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