I've removed/installed rudders on two different boats using divers. One was a Catalina 30 and the other is my current Ericson 26-2. It's not that tricky with a good diver, and preferably two when it comes time to install the new one. (Removing the old one is done easily enough with one person.)
A few tips if you go this route:
(1) It is EXTREMELY IMPORTANT that the diver not attempt to force the rudder post up the tube by wiggling the post back and forth. As you can imagine, the ruder post is a very long lever arm, and especially when the post is first inserted into the tube, the diver may be tempted to wiggle it back and forth to get it started on his way. Make sure he knows that under no circumstances should he do that. He should (ideally with the help of a second diver) line up the rudder post so that it slides straight into the tube with no side-to-side levering. This will prevent damaging the the attachment of the tube to the hull.
(2) Your rudder may or may not be positively buoyant. When I replaced the rudder on my E26, it was brand new and therefore not waterlogged. It had a slight positive buoyancy. The diver I used, who was highly skilled, attached a 5# dive weight (I believe) to pull the blade down so that the rudder post was pointing up. He did the entire job himself, but was very careful about inserting the new rudder as I described. According to my notes, the whole process (removing the old/installing the new) took 20 minutes.
(3) Both of the boats on which I did this were smaller than yours. That may be yet another reason to have two quality divers do this rather than attempting it with only one.
