thanks for clearing up that ... i wasnt sure if i could sail until i got that straight... <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

How about adding a thick shell of fiberglass and epoxy over the outside of your cracked casting. Pretty Cheap DIY. After rounding the sharp shoulders on the INSIDE of the rudder space, run the fiberglass around these curves with masking tape. This will hold the shell on. Add ss machine screws?
I have a H16 rudder casting cracked from the rudder bolt hole ($150 new- ouch): I bet it will last for 10 years in use.

well... as the song goes... if i knew then, what i know now!

After finding the small crack, I brought them to a guy to do a spot weld on... he ended up breaking off the end (where the bolt goes through the rudder, even though it was not near the crack) and then welding on a heavy block of alum (to hide his damage).

This doubled the weight, effected the helm, and he didn’t get the bolt hole back on straight (which caused me to have an offset rudder). My friend is a welder and saw the crappy job the other guy did. He asked me to bring the casting over so he could clean up the sharp edges and make it look a bit better. He is the one who noticed the bolt hole had been broke off after seeing internal welds….

I have learned a lot about treating alum… how to repair, and what not to do in the future. Another lesson was, Don’t assume replacement parts will be anodized, just because the originals were… make sure by asking and not leaving any details out when ordering over the phone. Hopefully others will learn from my lessons…

Thanks to all that provided info, even the details on alu-magn, galvanic corrosion and conductivity!