My 1973 E27 is a project. I have a couple of cracks in the rudder and I'm wondering whether it would be a big mistake to put it in the water this weekend and wait until fall to make the needed repairs.
On boats of this vintage everything is suspect until proven otherwise. I would not recommend venturing out into open oceans with a questionable rudder. Here is a link to the rudder issues on my boat and a few pictures. http://www.ericsonyachts.org/infoexchange/showthread.php?12527-Rudder-Rebuild-Replace
I would say at the least to remove the rudder and carefully inspect the shaft where it exits the rudder blade. Scrape away some gel coat and see what the crevice corrosion situation looks like, That's the most likely point it would actually break off. But with rust coming through the blade you definitely have some corrosion going on inside. weather or not its to a failure point can only be determined by tearing into it to have a look.
A whole new rudder is probably only about $1,200
If I were you I'd take a Dremel tool with a pencil-diameter-sized cylindrical sander and route a channel down that crack. Taper the channel a bit with a sander, lay down some thin strips of fiberglass and thickened epoxy, sand it smooth, paint it, and see what happens next season. Maybe a two-hour job, not counting cure time. The longer those cracks are submerged, the more water will seep in, the larger the cracks will get, etc.
Thanks much for the good advice. I'm "fortunate" that I sail at the bottom of Lake Michigan and can always see land so going off shore is not an issue. Since there's no play in the rudder and the rudder feels solid I think I'll follow Christian's advice and go sailing.