This is the standard 'Inter' rudder. Without looking I'm going to guess that the damage goes in far enough to be about 3/8" thick at its widest.

New semi-related questions:
Can fairing compound be polished smooth? I've never hit it with anything finer than 220 or so (usually just 80). It seems really porous to be on top.

How 'sharp' should the trailing edge be?

Thanks!