Prospective technologies assessment

Bouman et al., “State-of-the-art technologies, measures, and potential for reducing GHG emissions from shipping” compiles several measures that could deliver significant gains in energy efficiency and emission reduction. Most of the studies analyzed, however, are based on a single vessel or a small group of ships, disregarding the differences in design and operation across the broader fleet.

To address this, we use the MariTeam model to conduct scenario analysis through prospective modelling of novel technologies to be deployed in the maritime sector. We quantify the potential gains of new technologies and design innovations on shipping emissions, fuel consumption, and operational efficiency. To enable this, the MariTeam model is updated for prospective analysis of retrofitting and novel ship designs. This involves adding modules that simulate the performance of various retrofitting options (e.g., energy-saving devices, propulsion system upgrades, hull modifications) and emerging technologies (e.g., wind-assisted propulsion, alternative fuels, hydrogen, or battery-electric systems).

Air lubricaton systems

One example of this work is the assessment of air lubrication systems (ALS), which reduce friction between a ship’s hull and the water. We build on the work of Kim et al. (2023) “Potential energy savings of air lubrication technology on merchant ships” to analyze the gains from implementing ALS on six different ship types: bulk carriers, chemical tankers, container ships, general cargo ships, oil tankers, and ro-ro cargo ships. We then re-run MariTeam as if all ships had ALS installed in 2019. Results show the potential reduction in fuel consumption and emissions for each ship type under varying operational conditions and retrofit scenarios. This analysis enables a detailed assessment of how ALS can enhance energy efficiency and support the decarbonization of the shipping industry, while also providing insights into the economic benefits and return on investment of retrofitting different vessel classes with this technology.

Results indicate that the effectiveness of ALS is heavily dependent on a ship’s operational speed and the available surface area on its hull bottom. This favors vessels that operate at lower speeds and have high block coefficients (i.e., more available surface). To understand the differences between the three types of ALS analyzed, please refer to the short descriptions provided below.

BDR reduces the local density by injecting numerous microbubbles into the boundary layer, thereby reducing the Reynolds stress. At the same time, the effective viscosity is reduced due to an increase in void fraction, which consequently serves to suppress the turbulence of the flow and reduce skin friction (Park and Lee, 2018; ABS, 2019). As the injected air flux increases from this state, a transition occurs in which the air bubbles and the air layer coalesce with each other in the gas-liquid mixture.

When sufficient air is injected into the near wall region of the turbulent boundary layer, the air is aggregated with each other to form a continuous air layer separating the hull surface from the water flow. It was found that such a developed air layer, so-called ALDR can significantly reduce frictional resistance compared to bubbly flow (Ceccio, 2010; Elbing et al., 2013).

PCDR reduces frictional resistance by injecting air into a recess or cavity at the bottom of the hull to separate the lower part of the hull from water (Lay et al., 2010). A typical hull design for PCDR consists of a slightly downward sloping closure downstream from the starting wall of the cavity into which air is injected, which forms a partial cavity to trap the air. This drag reduction effect by the cavity air layer is associated with the design of the bottom cavity and the continuous injection of air to maintain a stable air layer (Wu and Ou, 2019).