Comparison of ship energy efficiency methods for bow foil technology

As part of efforts to achieve a 40% reduction in shipping emissions by 2030, the International Maritime Organisation (IMO) has recently enacted the requirement for existing ships (> 400gt) to pass an Efficiency Existing Ship Index (EEXI). The EEXI allows for the retrofitting of innovative energy efficiency technologies, such as bow foils, to ensure ship emissions compliance. Bow foils act to reduce the overall delivered power of ships in waves through both a reduction in ship motions and the generation of additional thrust. This paper presents and compares several methods for the inclusion of bow foils in the IMOs mandatory EEXI calculation. The results are based on a series of free running model tests with and without a passive, spring-loaded bow foil. The EEXI was calculated with and without the bow foil from measuring; the speed loss in a representative sea state; the increase in delivered power in waves at a constant speed; and the additional thrust force provided by the bow foil. The differences between the results highlight the importance of establishing a consistent methodology for the calculation of EEXI when using bow foils as an innovative energy efficiency technology

Combined performance of innovative biomimetic ship propulsion system in waves with Dual Fuel ship engine and application to short-sea shipping

Flapping-foil thrusters arranged below the hull of the ship are examined for the exploitation of energy from wave induced motions by direct conversion to useful propulsive power. In the framework of Seatech H2020 project (https://seatech2020.eu/) flapping-foil thruster propulsion innovation is examined, in combination with standard propulsion system based on optimally controlled Dual Fuel engine, aiming at an increase in fuel efficiency and radical emission reductions of NOx, SOx, CO₂ and particulate matter. In this paper the combined performance of the above systems is examined for a short-sea shipping scenario in the North Sea and two ship types. The analysis is based on a simplified approximation using data from systematic series. The results show that: (i) flapping-foil thrusters can directly convert kinetic energy from the ship motions into thrust to augment the overall propulsion in waves, (ii) additional thrust generated by the foils will enable the engine to operate in part-load without compromising vessel speed, resulting in an additional positive effect on its emission profile, and (iii) the foils can improve the dynamic stability of the ship.</p