After one year of conversations,
finally Zodiac Spain (a lot of thanks to Pere Garcia Director General de Zodiac Española) send me a new stainless steel prop with a pitch of 21,5, the boat (Zodiac Medline III) cames first with a pitch of 18,5.
The boat goes much better, not only is faster al lower rpm 51 mph at 6.000 (before 47 mph at 6.100), at medium range 2.500 3.000 run very smooth with a low consum.
Thanks for the help.
n.b. Now I have two props, the older can be use if the other brokes.