Particularly because the information being presented here makes it seem like our 2" shafts should be at least 4" for minimum security.

Here is a picture of a rather stout looking 45-50' boat that just pulled out to replace a prop. I don't know the make. It has a 66"x32" spade rudder that is on a 3" shaft (that bit underneath the hull and rudder cutout is only fairing and not skeg). I don't know the composition of the shaft or whether it is solid or tube.

It seems that if our two 20' separated little rudders on 2" shafts are undersized for a boat that doesn't heel or round up, certainly this single centerline rudder shaft is undersized for the loads it must see when it is healing and rounding up?

Maybe it is all that dynamically different loading constantly racking our rudders that makes our shafts so undersized?

Mark