Vortex at the tip of a classic long keel

Guillermo, Interesting. Thinking of your friends comments I'm not sure that you would want to cancel the vortex from a long low aspect keel. The lift generated is actually Vortex lift. If you could cancel the vortex you would lose lift.

For example that's why the Scheel keels were a failure ( increased drag and reduced lift), instead of encouraging an advantageous vortex separation from the spanwise flow the shape of the Scheel keel actually reduced separation and consequently L/D was a lot worse than a square end.

TE winglets sometimes increase vorticity rather than reducing it and are used for this purpose in some applications. So your friend might have a better lift regime for an entirely different reason to his presumption.