horstman rudder trimaran

When I bought my Tri-Star45 I noticed the main hull depth was 36" while the spade rudder is 42" . Now I find the rudder shaft has crevice corrosion just as we are ending a stay in the yard, so I am looking at options. 1. Replace w/ similar -- it's a heavy beast, 2" shaft and 4 or 5" of...