Tom Germer did some research and talked with some top rules guys to figure out exactly what the new rules for penalty turns mean for model boats. These two ISAF Q&A sheets help answer the questions we all have. Especially about doing extra turns for gaining significant advantage.

http://www.floridaec12.com/CC/ISAF_Q&A_J005.pdf
http://www.floridaec12.com/CC/ISAF_Q&A_M004.pdf