Spearfishing fins
FLAP C 4

FLAP blades, patented by C4, are born from the study of underwater behaviour by traditionally shaped blades, like Falcon, compared to the theoretical parabolic model of the blade under load.
Traditionally shaped blades, like Falcon, have an inherent limit to their bending that, due both to the minimum functional thickness utilizable for the material and the water quantity worked by each blade section, cannot possibly have that correct bending homogeneity, the most possibly analogous to the perfect parabolic curve C4 is since the beginning searching for its fins.

Nature evolved fish in such a way that they assume, while swimming, a bending progressively parabolic from head to tail, exactly for exploiting to the maximum degree the non-compressibility of water.