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Posts: 102
| Your numbers are confusing to me. If you google prop slip calculator and plug your numbers into the utility programs you find, with a 19 pitch prop you would have to be 12% better than zero slip to make 64 mph and that isn't possible.
From what I can find, your gear ratio on a 2008 250HP is 1.85. Unless you have a new gearcase with the 1.71 or whatever they went to in 2010 it just doesn't add up. (Even with a 1.71 gear ratio you would still need to be using a 21 pitch with 5% slip at 5900rpm to hit 64mph.)
Either your speed reading is way off which is doubtful if it is gps, your rpms are way off or you don't actually have a 19 pitch prop. With a so-so 10% slip at 5900rpm you"d would need a 24 pitch prop to hit 64 mph. At a unbelievable perfect zero percent slip you would still need a 21 pitch at 5900 rpm.
If you have a prop shop nearby they could check your pitch against a master and see if you really are running a 19 pitch or if your prop has been reworked to something entirely different. A dealer could check your tach reading to make sure it is right. Without knowing which data is off, picking a new prop would be awful hard. |
