This Main Rudder Assembly is a direct replacement for your Vibe Shearwaters stock rudder assembly.  Please note, this assembly will not allow the rudder to lock into the down position.  This makes using the SAI Rudder Assembly with a rudder mounted Bixpy unusable in reverse.  It will however, help protect your rudder and rudder assembly as the rudder can pop up when it strikes an object.

SAI Shearwater 125 Main Rudder Assembly