Rune Eurenius in Gothenburg, Sweden, is paddling around in a Sea Racer with an integral rudder. He based it on an old sketch that has accompanied some of my plans for at least ten years, and made major imporvements to the idea. Here is a short presentation with photos of his version: http://www.thomassondesign.com/en/news/exciting-rudder-solution .

The main advantage is that the rudder does not stall the way a separate fin rudder does when angled out. The water flows from the hull on to the rudder with much less turbulence – improving the efficiency like a fixed skeg in front of a rudder.

The small photos links to a Swedish kayak forum where Rune showed his rudder construction: in short, he used a bicycle pedal for the bearing and a wind surfers fin for the skeg part...

Rune's Sea Racer is also in three parts to fit in his small car: http://www.thomassondesign.com/en/news/three-part-searacer-rune-eurenius