The ornamental design for a surfboardfin mount, as shown and described.
FIG. 1 is a front perspective view of my new design for a surfboard fin mount;
FIG. 2 is a side elevation view of the fin mount shown in FIG. 1;
FIG. 3 is a front elevation view of the fin mount shown in FIG. 1, of which the rear elevation view is a mirror image thereof;
FIG. 4 is a top bottom view of the fin mount shown in FIG. 1;
FIG. 5 is a bottom view of the fin mount shown in FIG. 1, wherein the broken lines indicate matter for environmental purposes only and form no part of the claimed design; and,
FIG. 6 is a perspective view showing the fin mount used to mount a surfboard fin (in phantom lines) therein.