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Home. Association Forum Ships Store Cruising Racing Technical Tips Photo Gallery - New Boat Search - Updated Manuals & Brochures Swap Meet Links Officer Flag Line & Staff Bylaws & Constitution   Members Area Join the Association   Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.	Windblown - Measuring Pitch This tip submitted by Andy Paras Measuring the pitch of a propeller is not as mysterious as some make out. I asked the guy at the local outboard shop and judging by his reaction, I may as well have asked him how to split the atom. Then I looked it up in a book. All I needed, they said, was a ruler, protractor, carpenter square, and scientific calculator. An advanced engineering degree was optional. I thought up a technique using only a pencil, ruler, scotch tape, and string that anyone can do in about two minutes. (1) Make a small pencil mark 3 1/2 inches from the edge of a table top. (2) Center the prop (aft side up) on the mark so that one blade is perpendicular to, and extending beyond the table top edge. (3) Using the edge as a guide, place a ruler on the face of the perpendicular blade. Mark the point where the ruler meets the table top. (5) At this point, tape a length of string. You need about 2 1/2 feet. (6) Make a second mark 22 inches from the first so that the prop blade is between the two marks. Place a ruler perpendicular to the table at this point. (7) Pull the string taught parallel to the table top edge, so that it just touches the blade face and crosses the ruler. (8) This distance from the table top to the string, shown on the ruler, is the pitch. Why does it work? Pitch is defined to be the theoretical forward distance a prop will travel in one complete revolution. A point on the blade face at any convenient distance R from the center will describe a circle in one revolution, traveling a distance equal to 2 x pi x R. If you let R = 7/2 (3 1/2 inches) and assume pi to be around 22/7, this works out to 22 inches. As the point rotates, it advances (forward) a distance proportional to the slope of the blade face at the point. Your big right triangle has exactly the right slope, and (horizontal) length to produce the (vertical) pitch.