To JKW 1939: Thanks for your input. I have done the Scratch Test and both marks line up. I think maybe I have the wrong Prop (9P A1) This I believe is a 9" Pitch which may be too much or too little for my 16 Ft. Alumacraft boat. Also is a 3 blade prop suitable? The OEM prop was a 2 blade. Any Pitch-men out there who have any ideas?