I am sorry I didn't reply sooner. this is my data for the Helms -25 rudder. I hope this helps. I wouod look at the 25 ft catalina as a donor boat, very similar. My current rudder is modified but I can get some pictures if that helps. Please let me know how I can help.
I have a lot of data for the Helms 25 only, I wowuld appreciate a picture of your boat, Hull # and name etc for my Helms files..