rudder blade

[Scofield]

I need a prediction method or something similar for rudder blade area prediction for motoryachts.
I am working on 21m motoryacht and i have to design a rudder for the boat.
I do not know a prediction method for the rudder blade area and rudders form.
If anyone has advice a resource about this subject, i will be happy.

[FAST FRED]

Go to the Professional Boat Builder site, and find an article in their free archives.

FF

[Olav]

The aforementioned article in Professional Boatbuilder (written by Eric W. Sponberg iirc) is a really good source to get an idea about rudder design and engineering.

If you want to go simply straightforward I recommend to use the GL Rules and Guidelines which can be found here (http://www.gl-group.com/infoServices/rules/pdfs/english/glrp-e.pdf). Have a look at Part 3 (Special Craft) / Chapter 3 (Yachts and Boats up to 24m) / Section 1 (Hull Structures) for rudder sizing and scantlings. Other Classification Societies may have something similar but GL is what I'm familiar with.