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What this video covers

Nigel Calder explains the trade-offs of running an oversized propeller on a sailboat, responding to a student who discovered their 19×14-inch prop was far larger than the calculator-recommended 17×10-inch.0:14 An oversized prop reduces wide-open-throttle speed and loads the engine more heavily at lower boat speeds.1:02 On a sailboat where the engine rarely runs at full throttle, that loading improves fuel efficiency and reduces carbon buildup in the engine — benefits Calder says he applies on his own boat.1:16 On a powerboat run at wide-open throttle for extended periods, the same oversized prop will overheat the engine and risk serious damage.1:27 The deciding factor is duty cycle.1:38 On prop condition, Calder cites his own testing: a propeller left in the water for one month accumulated minor barnacle growth that drove fuel consumption up 50% or cut speed by roughly one knot at a fixed throttle setting.2:06 He concludes that testing a damaged or fouled prop produces unreliable data, and that prop degradation alone can meaningfully raise fuel consumption — making replacement worthwhile.3:00

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