[frenchman_in_ny]

A number of high performance sailboats have front rudders -- it's called CBTF or Canting Ballast Twin Foils. One example is the Schock 40 [1].

[1] http://www.wdschock.com/boats/schock40/s40_specifications_b....

[astrodust]

The down-side to a front rudder appears to be that it creates turbulence underneath the hull of the boat, where the bow rudder creates turbulence in the water behind the boat.

A rudder also creates drag. Having drag behind the boat is a lot easier to deal with, it has a damping effect on movement, than drag on the front which would make it more twitchy and erratic.

For a racing boat maybe you're willing to deal with twitchy.

[Someone]

Aha! I knew that these existed, but didn't know they had two rudders/foils, too. Sailing boats that can't really be used if their engine isn't running :-) (they need power, typically hydraulic, to move the keel during sailing)