Where are you located? Not
Canada I hope, as I would think your rudder would have been damaged when the water froze when hauled. That happened to our previous
boat so after that I started drilling a small drain hole after hauling, and sealed it before launch.
I was going to suggest what I have since done on our
current boat, but my rudder posts go to the bottom of the rudders (skeg supported) and is on the leading edge of the ruddesr. I drilled two small holes near the bottom of the rudder from the leading edge through both walls of the pipe. This of course drained the rudders, and before launching I plugged the holes with
epoxy. Now when hauling out, or anytime for that matter, I stick a tube down the rudder post and
pump the water out.
This would not be effective with your rudder. Regardless, I don't see how filling the post with foam would help. Besides, if the top of the rudder is below the waterline, I expect that water is seeping between the post and the
fiberglass. That's a difficult connection to make. Perhaps if you are using
epoxy you will do better than the
builder did.