Speed
Dear Bob: Thank you for your letter. It is very difficult to determine whether you vessel will produce a greater speed then what you are currently obtaining. As your vessel increases in speed it will begin to develop a bow wake, which at some point, becomes impossible of passing through. At the point the vessel exceeds its bow wake it is the point which the boat has begun to plane. The closer the vessel gets to that theoretical hull speed, the greater the required amount of Hp is needed to get it to that point. By changing your propeller to a larger diameter and greater pitch may only create greater load to the engine, which may not allow it to obtain the needed Rpm’s / Hp / torque. By changing your prop, you may only exceed in increasing the boat speed at lower Rpm’s and not increasing the overall boat speed. A simple test you can do to determine if your running gear can handle a greater amount of propeller load, more diameter more pitch greater speed, is to run the engine to its maximum throttle. If the Rpm’s exceed the rated max Rpm’s, recommended by the engine mfg., increase the pitch to increase the load which increases the speed and lowers your Rpm’s. If you increase pitch by 1”, you can except a 12% decrease in Rpm’s. Hope this helps. Sincerely, Kevin L. Woody
