Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post. Is a bigger diameter prop faster?Diameter usually increases for propellers used on slower and heavier boats, and decreases for propellers intended for faster boats. A prop with more diameter has more total blade area, which allows it to handle more power and create more thrust to move a heavy boat.
How does propeller size affect speed?For most vessels, a small increase in diameter means a dramatic increase in thrust and torque. In higher speed vessels like mentioned above, however, a larger diameter equates to high drag. Diameter generally increases for props on slower boats and decreases on faster boats.
How much difference does prop diameter make?A prop's two dimensions each affect performance in different ways. For every inch of change in prop diameter the RPM varies by about 500 RPMs (up or down) and every inch of pitch changes the RPM by approximately 150 to 200 RPM.
What happens if your prop is too big?Sailors rarely think about the size of their propeller, but it is an important component of your boat's drive system. Overpitched and oversized propellers can cause an engine to work harder and hotter than it should and not allow it to reach optimal cruising rpm, resulting in poor performance and decreased engine life.
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