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.
Research and development results concerning flapping foil thrusters, supported by extensive experimental evidence and theoretical analysis, have shown that such systems, operating under conditions of optimal wake formation, can achieve high levels of propulsive efficiency; see, e.g., Triantafyllou et al (2000, 2004), Taylor et al (2010). Additional data concerning thrust coefficient, foil flexibility and Reynolds number effects can be found in the experimental systematic study by Vermeiden et al (2012). Based on the above results, the last period biomimetic propulsors with the ability to convert wave energy directly into thrust augmentation is subject of intensive investigation.
For ships the application of bow mounted flapping-foil thrusters positioned below the waterline, which exploit the energy from the wave induced motions to generate a net positive thrust augmenting the ship propulsion, could lead to significantly reduced engine loads. A schematic presentation of biomimetic foil thruster arranged at the bow of the ship, with support for elevating/lowering the system in the water is shown in Fig. 1. In real sea conditions, the ship's propulsive power demand typically increases above the corresponding value in calm water for the same speed and at the same time experience undesirable wave induced, oscillatory, heave and pitch motions. The application of flapping foil thrusters, coupled with optimally controlled Dual Fuel engine technology, is expected to yield significant fuel savings and emission reductions.
