Best prop pitch? 12" or 13"?

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T Man

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I took my new (to me) 1652 Lowe John out today for a shake down run. Everything worked fine except for the spun hub. For what the dealer wants to re-hub I can buy a new one. Using Mercury's configurator, I am down to a 12 or 13" pitch on my prop. Mainly this boat will be used as a duck rig on strip pits (less than 1 mile long), but will see big lake (Grand Lake) use during the summer months.

Motor is a 25hp mercury, boat is a 1652 Riveted Lowe with a console. Rpm is unknown, as is boat weight (I am guessing around 550 with motor, somewhere around 1000 with guys and gear)

12" seems like the ideal balance, but will there really be much top speed difference between a 12 and a 13, or should I buy a 12 now and then get a 14 later on to swap on when running bigger water?
 
If the 12" works fine and achieves full RPM with a normal load, then use it.

The 13" probably wont pick up much MPH, if any. Little motors (like under 90 hp) are WAY different than 150+. On a 150 for instance, if a 21" will pull 6000 RPM @ 60 mph (for example) going up to a 22" might pick up 1-2 mph but the motor will drop RPM back to, say, 5850-5900.

On a "little" motor (most portables), going from a 12" at 6000 RPM to a 13" on the same boat/motor may drop 500 RPM...or in some cases, more. And then with that 13" it's possible to lose a TON of holeshot. On my yamaha, going from 10.5" pitch to a 11 1/4" pitch dropped the RPM 650. Blade design is almost identical on both, and I believe the blade rake is almost identical. No change other than going from 6400 to 5800 and picking up 3-4 mph (F25 Yamaha supposed to be 6000 RPM max, ignition limiter cuts spark at 6400, then is back on at 6200-ish).

You need a tach. Plain and simple. Tuning without it is a crap shoot, at best. They aren't expensive.
 

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