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→Number of Blades
With more blades, vibration and noise are reduced, and thrust is more evenly distributed. For example, a boat with 200 shaft horse-power and three blades has 66.6 hp per blade. With five blades, the power distribution is 40 hp per blade. With more blades, a propeller can be smaller. However, larger propellers are better at moving water. Small blades move less water. To compensate, they have to turn faster. But increasing rpm reduces efficiency. Other factors also come into play. For example, higher block coefficients in the hull design reduce propeller efficiency.
[[File:TrawlerPropellerRicePropulsion.jpg|thumb|300px350px|left|Adaptation by Rice Propulsion of the skewed design to a trawler – Photo with permission © Rice Propulsion, http://www.ricepropellers.com/]]
Again, like so many boat design issues, the optimum is a compromise between several factors. Generally, the choice is between large slow turning and small fast turning propellers with an increased pitch angle.