Flapping foil is an interesting concept because of its ability to generate thrust against the wave motion using wave energy. However, it is yet to be successful in the real world applications even after several years of research on it. Researchers have been developing this to make it useful for real structures from more than 120 years and we are yet to see any drastic change. we have seen so many short-term success ideas like a substitute for the propeller, thruster or stabilizer of ships and other ocean-going structures but yet to find a big impact of flapping foils on the ocean and shipbuilding industry. If we study or do some experiments with the flapping foils in an ocean laboratory, we can find it very much interesting since it works on renewable source of energy, it is more efficient compared to the conventional ship propellers and can also be useful for the stealth naval vessels due to its motion similar to the dolphins.
Foils can be made to flap using several methods like using a spring or elastic plates or something which can provide restoring force for better flapping. There are a lot of uncertainties involved in the analysis of flapping foils blocking its progress towards real applications. I hope this old but very useful concept get a good success very soon to change the ship and ocean industry in several ways for making our air and water pollution free in an alarming global warming situation.
Thank You!