Re: Is external rudder a good idea?
With an inboard rudder you lose the most useful streering option of all, steering via trimtab either for a vane , manual steering, or inside steering. I dont see any options lost with an outboard rudder.
An ex airforce friend mentioned a large cargo plane which was totally controled by trimtabs. At rest, all the control surfaces hung down, and only came to life as the plane started moving. It was so powerful that they had to put in some resistance, as a pilot could easily rip the wings off, without realizing how much force he was putting them under.
Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"