Fig. 8. Surface pressure contours (N m^-2) on the pectoral fin at three instants when the peak in the thrust occurs. (A,C,E) Front, (B,F) back, (D) ventral view. (A,B) t=0.963 s (32% downstroke); maximum and minimum pressure occur below and above the leading edge of the fin, respectively, producing maximum thrust (-x direction) and lift (+y direction). (C,D) t=1.065 s (84% downstroke); maximum and minimum pressure occur above and below the leading edge, respectively, in the outer half span of the fin, producing minimum thrust. (E,F) t=1.167 s (68% upstroke); high-pressure region extends for more than half the dorsal side of the fin while the pressure on the ventral side is almost uniform, with a region of minimum pressure near the outer leading edge, producing a maximum thrust.

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