The ecological transition of shipping is being driven both by growing customer demand for low-carbon transport services and by the tightening of international regulations on pollutant emissions. To meet this demand, shipowners are for the most part moving towards the use of alternative fuels: the gradual abandonment of heavy fuel oil for marine diesel, followed by LNG, and then tomorrow towards biofuels and hydrogen. These last two fuels certainly represent part of the solution, but two other levers are largely under-evaluated and under-used: speed reduction and the use of wind propulsion.
Price, speed, punctuality, and carbon footprint are the four key parameters of a transportation service. And the integration of wind propulsion in the energy mix of ships must generally take into account a trade-off between these parameters in the following order:
1. Punctuality: no trade-off possible
Generally speaking, no compromise is possible with punctuality. Sea transport is just one link among others in a logistics chain (truck + train + sea + truck again). If one wishes to enter the conventional transport market it is not possible to arrive 3 days late under the pretext of a lack of wind. The economic consequences, such as outdated goods, are too important. If the ship arrives late at its destination, the entire post-delivery logistics chain is penalised. This implies that wind can never be the main means of propulsion. It will have to be accompanied by other means, such as mechanical propulsion.
2. Speed
The speed often depends on the sea route the cargo ship is following. If the freighter is on a round trip or if it is travelling from one destination to another. In other words, speed is not necessarily negotiable as such, it is dependent on the journey. And yet it is from speed that the rest derives: the price and the percentage at which the sails are used.
3. Fuel economy
It is directly related to the desired speed. If a customer agrees to give no speed and time requirements, the sails can be used 100%. If, on the contrary, the client wishes to go fast at 20 knots due to the nature of goods being transported, the boat will run permanently on the engine, and the sails will only slightly reduce fuel consumption.
Between these two extremes, the speed parameter should be seen as a cursor that is positioned according to the CO2 savings that we wish to achieve:
8 knots = very low speed = 90% sail / 10% engine
12 knots = low speed = 60% sail / 40% engine
15 knots = average speed = 35% sail / 65% engine
4. The price
Generally speaking: the market was not ready to pay any extra costs 4 years ago. Today it seems to accept an extra cost of 20-30% for a low carbon service.
The magic balance
Today, for average transport speeds of 15 knots, a saving of around 30% can be achieved. The construction of a sail freighter costs about 15% more than a conventional freighter. This results in higher CAPEX (capital expenditure), which in turn leads to fuel savings. The advantage is to be more resilient: if the price of fossil fuels rises, our transport price is less impacted than that of conventional ships.
There are several sailing transport projects in Europe. Each one adopts quite distinct commercial choices. Some favour a radical and zero CO2 approach, which implies low-speed transport and a high price, which is only possible for products with high added value. Others address the conventional market with a less radical approach, but one that allows them to address larger markets and therefore greater savings in absolute terms.
The world fleet is made up of about 50,000 cargo ships. The average life expectancy of ships is 30 years. If the IMO (International Maritime Organisation) wants to respect the limits it has set for itself, namely a 40% reduction in CO2 emissions per transport work by 2030, pursuing efforts towards 70% by 2050, compared to 2008, it is important that maritime transport should begin a rapid energy transition. It is not conceivable to wait for the gradual renewal of this fleet by sail freighters, it will be necessary to equip existing vessels with sails. It should be borne in mind that wind propulsion is not suitable for all types of ships, nor for all shipping lines in the world.
Weather routing
Thanks to wind statistics from the last 10 years, it is possible to simulate a large number of trips using powerful routing software. Based on the average fuel savings achieved on these simulations, it is possible to estimate the savings that can be achieved on a given shipping line, with a given vessel, depending on the seasons and the weather regime. Furthermore, once the ship has been built and commissioned, this same routing tool can then be used to plot the most suitable route for the ship according to the weather forecast for the coming days in order to make the most of the wind on the planned crossing.
The first modern sail freighter over 100 metres long
In 2018, Zéphy et Borée with the joint venture of the maritime company Jifmar Offshore Services - won a major call for tenders to transport the Ariane 6 rocket. The ship will be commissioned in 2022 and construction began in February 2021 in Poland. The different elements of the rocket are built in different European countries, they will be collected by our boat in the ports of Bremen, Rotterdam, Le Havre, Bordeaux, Livorno, and transported to Kourou in French Guiana, from where the Ariane rocket is scheduled to leave.
Designed by the Bureau VPLP Design, this ship will mark a turning point for modern sailing transport, taking it from a marginal solution to a real future solution for the world fleet. The ship is 121 metres long and 21 metres wide and is equipped with four wings with a surface area of 363 m² each.
