Someone is wasting a lot of engine power by not putting nozzle around the rudder. But then who are we, when no doubt that is the way a professional naval architect designed it - or was it someone or something else with less knowledge of what a kort is about? Lookout AI will be taking over our comments soon!!😭😭😭

Probably a retro fit. Fixed position propeller with a following rudder. Likely added a ring (nozzle) to the existing rudder or a new rudder with ring.
Lew
Florida ⛱️, USA 🇺🇸