I had ran across this some time ago, but forgot all about it… thanks to Klaus for giving me a link to get some research started back on this.

The Kitchen Rudder is a mechanical "clam shell" arrangement that can be used with a fixed prop to provide steering and reversing through moving the clams in various configurations. The reversing functionality reminds me of a jet aircraft’s thrust reverser, if you are familiar with those.

The design was used by the British Navy on smaller launches, etc. for some time, apparently.

There was an extensive discussion on the BoatDesign.net forums at this link. Some pictures/drawings are included there and a larger one from the original U.S. Patent here.

I had the thought of combining this with some of the electric motor "pods" for steering… would be a different alternative to the "steerable pod" that is seen, although I think that would probably be adding complexity instead of taking away. You don’t need the "reversing" aspect with electric, but the steering you do, and the advantages/disadvantages to a prop shroud are still there. Similar to a kort nozzle when in "forward thrust" mode.

The original patent seems to be 1,186,210 (click the "Images" button at the top)

A later related one is 4,895,093.

I’m attaching a writeup and graphic I found at the Artemis Steam Launch website.