Making inland waterway transport more efficient and more sustainable is one of European Commission goals promoted through the NAIADES II package "Towards quality inland waterway transport". Inland navigation faces many challenges such as over-aging fleet, increasing fuel prices, climate change, and stronger environmental regulations regarding air emissions. To tackle those issues, reducing ship speed is an adapted solution. Indeed, a ship sailing at a reduced speed will emit less greenhouse gas and consume less fuel. This practice, also known as “slow steaming”, is already used for many maritime commercial ship sectors such as tankers, bulk carriers and containerships, but rarely applied for inland navigation. A basic application of slow steaming consists in sailing at a speed lower than the vessel’s design speed. More evolved slow steaming practices involve speed optimization algorithm taking account of several factors (weather forecast, current, trim, draft and water depth) [Psaraftis & Kontavas, 2014]. Some industrial products such as “Eniram speed” (www.eniram.fi/product/eniram-speed/) already exist and are frequently used for maritime navigation. However, to the knowledge of the authors, no such products exist or are used for inland navigation.
The aim of this article is to develop a speed optimization software for inland navigation allowing to reduce fuel consumption by specifying a recommended sailing speed for each leg of the travel. For a given route, the water depth and currents are predicted with a 2D hydraulic model (Telemac 2D). To each leg of the route are then assigned a mean water depth and current velocity. For each leg, resistance curves are obtained with a ship resistance model, based on a metamodel approximating CFD calculations for ship resistance [Linde et al., 2015]. The fuel consumption is estimated with the model developed by Hidouche & Guitteny [2015]. The gradient projection algorithm [Rosen, 1960] is used to minimize the global fuel consumption for the itinerary. This model is used to simulate a real case: the itinerary of a 135 m self-propelled ship on river Seine, between Chatou and Poses (153 km). The optimized fuel consumption is compared with the non optimized fuel consumption, based on AIS speed data gathered on this itinerary. Different river discharges (low, medium and high) and sailing directions (upstream and downstream) are studied. The effects of the ship trajectory and travel duration on fuel consumption are also investigated.
The results of those investigations showed that optimizing the ship speed led to an average fuel saving of 8 % and that using an optimal track and including real time information such as lock availability and river traffic can lead to additional fuel savings. This model, although still at an early design stage, needs further investigation and validation, but could be a useful tool to make inland navigation more sustainable.