[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.