Two or three blade propeller
Dear Mr. Lindberg: Thank you for your letter. When either a two or three blade propeller is set up correctly, meaning they are set to optimize the engine output, they should produce apx. the same running speed at the same rpm while motoring in flat calm seas. It is when you begin to motor into a heavy wind, sea or any adverse condition that the two blade propeller will begin to loose efficiency in the form of speed. When the three blade is confronted with the same adverse conditions, this speed lose is less apparent. It will also be found that the three blade is much quieter and smoother then its two blade counterpart. As for the size needed it is often thought that you would use the same diameter as the two blade but with one inch less of pitch when comparing it to the two blade. As for what size to use, we will need to know the current engine, transmission and propeller combination. Our records show that there are apx. three different running gear combos available. Is it worth it? I’m sorry to inform the group that as an average we sailors have a tendency to speed as much as 70% of the time motoring! If you are one of those then the three is well worth the $200 to $300 investment. Racing? Not a chance your sailing speed lose apx. ½ knot in medium air. This is why company’s like PYI, Martec, Autoprop and others manufacture propellers with the capabilities of producing minimal drag with minimal efficiency lose for motoring. Hope this helps. Sincerely, Kevin L. Woody
