My mast has a groove on the froward side of the mast. runs all the way to the top. So does the Z-Apar on a friends '93 HUNTER 33.5. Does not appear on the earlier 'G' model at the marina.Anybody know what it is used for?Is it perhaps to center the whisker pole or spinnaker pole loop? I want to add such a device ... any suggestions? TRhank you, Bill Jaworowski,Carlyle Lake IL>