edges of a sail
      Foot - the bottom edge of the sail
      Head - the top edge of a 4 sided sail
      Luff - the forward edge of the sail
      Leech - the aft or trailing edge of the sail
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corners of a sail
      Tack - where the Foot meets the Luff
      Clew - where the Foot meets the Leech (aft)
      Head - where the Leech meets the Luff on a 3 sided sail
      Peak - where the Leech meets the head on a 4 sided sail
      Throat - where the Luff meets the Head (edge) of a 4 sided sail
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