Many rudders are accidents no longer waiting for places to happen. This is partly due to design faults, but also to cheap construction methods where the internal post and/or tangs are too weak, of insufficient length or where there are voids in the surrounding area - beware foam cores in rudders! The illuistartion (right) is a typical production type where fibreglass skins are bonded to a central foam core.

Much more work, but considerably stronger is a hefty post and full-width tangs made from 316 stainless steel, literally encased inside a solid cedar-epoxy fabrication - as shown below. After all bonding has been done, the cedar is shaped to fit these templates before being encased in double-diagonal glass cloth bonded with epoxy. It is finally sanded and surface finished with epoxy/microlight bog

Note the tangs (top of left picture) that span the full width of the rudder blade
The odd-shaped pieces in the right-hand picture are templates for the top, mid and lower sections used to shape the outer surface

Here is another excellent way of rebuilding a rudder - by Britt Finley S/V Restless. The internal structure in the right-hand picture replaced the former degraded tangs shown in the left picture