| Author | Message | ||
     Gary Hendrickson (Garyh) Rating: N/A |
Submitted by Gary Hendrickson (#094), Class Rules Committee G & S Drawing # 035-09A describes a solid lead keel about 48 inches tall, with a plumb trailing edge. The root chord (length of the keel section at the top) is 60 inches long. The tip chord (length of the keel section at its bottom) is 36 inches long. Maximum thickness of keel at any section = 10% of chord length. i.e. 5 inches thick for a 50-inch long chord. Maximum keel thickness is always at 40% along the chord, for any keel section. The 9.1 keel section shape appears to be a “composite” NACA foil shape. Its entry shape appears similar to NACA 64-010 The design entry shape (first 1” - 2”) of the 9.1 keel is rounded or radiussed, rather than a wedge shape found on a few 9.1 keels, which was caused possibly by extra grinding required to even up the shape after molding. The trailing edge design width varies from 5/16 inch to 3/16 inch, from top to bottom. Most keels actually measure quite a bit thicker here. Where this is the case, measurement will show that the keel’s section chords are 3/8 to 3/4 shorter than called for. This was likely caused by substantial grinding of the trailing edge to remove residual roughness and unevenness from molding. The trailing edge should be square, not rounded. The bottom edges of the keel should be relatively “sharp” all around. Occasional light grounding on rocks & stones can grind off a pretty substantial radius on these edges, but they need to be sharp to control water flow and maintain keel efficiency. In a cradle, this area is difficult to access and fix, unless the boat is raised up and set back down propped up with the keel accessible, as has been done by some. A check of the shaping and dimensions of a number of keels in the Lake Michigan racing fleet has uncovered no significant deviations from overall design shape and no significant differences in specific dimensions or attributes from keel to keel (i.e. no keel redesigns). They were generally in pretty good shape. Several conformed especially well to the design drawing dimensions because they were either early keels or had been professionally faired with accurate templates. Keels tended to be oversize in thickness rather than undersize – After molding, a layer of fairing compound was spread on over the lead at the factory to smooth the surface and prepare for a gel coat finish. |
