I have never before seen a rudder with a drain plug along its foot. I have always been schooled that water in a rudder is potentially dangerous because of the prospect of corrosion of the armature and the subsequent 'blowing apart' of the structure this could cause.
I guess this is more pertinent where the rudder is solid and fully bonded to the armature.
It appears some manufacturers have fitted drains. Whether these are inserted at the point of manufacture, or retro fitted is unknown. A recent haul out by a friend in the Caribbean caused some consternation due to the amount of water which appeared to come from the blade. I am not sure if it came from the drain, gudgeon straps or the heel pintel.
I wonder if perhaps fitting a drain is a practice for racing boats where a light weight rudder could aid buoyancy aft, and keep the overall displaced weight down.
Anyway I would like to hear from anyone who has a rudder drain fitted, or who knows anything about them.
"if at first you don't succeed....Redefine success"!