Terms Involved in Understanding Runner Design
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by Henry Bossett - DECEMBER 1987 CROWN - The height a runner lifts off a flat surface. To fully understand this it must be related to a length also. For instance, I feel that .008 of crown is a good point of reference. so I always check runners to see what length of the runner is .008 or less from a flat surface. FLAT - The portion of a runner that is absolutely true flat when checked against a flat surface. I'm sure that with a microscope you could show that what looks flat to the eye is not really so, but to the eye, no light would show thru this area of the runner when backlit. LEADIN/ENTRY - In my case, the area of the runner in front of the portion that is .008 or higher off a flat surface EXIT/EXHAUST - In my case. the area of the runner behind the portion that is .008 or higher off a flat surface. SHARP - That section of the runner edge that is in fact brought to as fine an edge as the individual can achieve. This area will not reflect light back from the point. DULL - That section of the runner edge that may hold you on slightly soft ice, but that is rounded just enough to reflect light from it's point. PIVOT POINT - The location of the runner bolt hole in relation to the overall length of- the runner, and or the flat portion. HARDNESS - The degree in terms of a standard Rockwell scale that the runner or it's edge has been made more resistant to wear. MATERIAL - Many different alloys of steel are available to make our runners from. Each has it's tradeoff's from ease of sharpening, through ease of maintenance. Below is a diagram showing some of these terms. It is not to scale. If I only had one set of plate runners, I would design them to have 20" of .008 crown, with 5" of flat. For sticky conditions, or for small lakes and light air. 12" of .008 with 2" of flat would help acceleration at the start and when tacking, but would not have the "Top End" speed of the longer set. Wood runners in spite of their longer length seem to work with similar .008 and flat.
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