With some winged keels, the difference in performance vs. a standard fin isn't nearly as big as lot of folks think. Depends on the keel
design. But ballpark, on a production boat
you're looking at 10sec/mile (or less) vs. a standard keel
. AKA less than the difference between a good, & a poor finish on the boat's bottom.
Part of this is due to the fact that winged keels can be designed to maximize the end plate effect, thus increasing the efficency of the fin section above the wings. So basically they trick the water
into "thinking" that the keel is deeper than it really is.
The other design perk which comes with them is that they can be drawn so that the number & size of the vortices coming off of the keel are reduced. Which means less drag, & thus, better performance.
The next time you're traveling, take a look at some of the aircraft & see what's on the tips of their wings