Hi Footski, I have had several holidays on narrow boats and after some small calamities on an early one, I found out about the rudder. You can just see in the underside picture of the model that the rudder has a round part on the top with a hole in it.
This crescent shaped part should be high enough to prevent the rudder from turning under the hull. Rudders tend to be quite long and not very deep, so if it can turn back and under the boat, it will hit the propeller. I have heard this noise and do not recommend it as an exercise!
The shape of the rudder stem has a purpose, it snakes up to the stern and then at the point above the rudder stock it stops. It is here that the round section tiller is slid into place. When the boat is closed down for the night the tiller is taken below which makes it extremely difficult to operate the rudder, it is a simple but effective security device.
best of luck Roy
