I have recenlt attempted to upgrade my prop from the standard two blade prop that has hung on the shaft of my 31' O'day with the Universal M-18 (14hp @3000rpm). A local prop shop suggested a 15x10. At that point the motor would only turn 2770 rpm and made a significant amount of smoke. We repitched to 15x9 and I got to 3000rpm but with smoke at the top end. The mechanic and I decided that to repitch again might compromise the advantages of the three blade. Can any one advise me of their 31'O'day similarly configured (engine/shoal draft) and the success they might have had up-grading to a three blade and the specifications of their prop? Thanks for the help.