Wow, seems like I just answered a similar question.

A company called "Mack" markets a drive system,
http://www.mackproductsrc.com/1233%20PT%20109%20S.htm
http://www.mackproductsrc.com/pwr_pkg_p2.htm

However, they are only dual shaft.
The two that I have seen run, perform beautifully. I don't recall the rudder setup though.
One guy actually lit all the dials.

In my opinion anything is possible if you can build it small enough.
So building it with a triple rudder would be nice, but it isn't really necessary for boat handling.