Fuzz wrote:. . . if you can come up with a way to not drop it very often you will be happy. One thing I have done is to bore a hole in the rudder so you can turn it and then slide the shaft through the hole when you need to remove it from the boat.
That is very common on large boats and can be done on the ST21: a hole in the rudder filled with removable material but it is not necessary in this case. To pull the shaft, if needed, you remove the rudder. Remove the keel shoe then the two rudder shaft collars inside, slide the rudder assembly down. It is a shallow boat, no need to dig a trench or to lift.
The keel shoe can also be made from two parts bolted together. That way you don't have to remove the whole keel shoe.But again, in such a shallow hull, everything is easy to reach and how often are you going to pull the shaft?