You guys should play with prop pitches all you want, but with an induction tach installed for that purpose. OB's runs on min and max wot rpm range factory stated which varies from manufacturer to manufacturer.
Wild guessing, ear tach propping is no bueno, each boat and load should have a motor running to at least middle of its wot rpm range, but most likes to prop for max wot rpm range.
Happy Boating
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