|Unless you have a very early boat on which a sliding gooseneck was the equivalent of the cunningham and halyard as your luff-tensioning tool, the gooseneck should be fixed, usually with a machine screw in the track above and below the gooseneck slide, if I remember aright. Of course, if you are still using the roller-boom to reef, you might want to keep the sliding gooseneck and just add a downhaul tackle below the boom, but I think you would be happier fixing the gooseneck position and adding a cunningham. I'm sorry, but I cannot tell you at what height to fix the boom because my boat is put away.
Anyone else out there have access to a mast so they can measure the distance between the slug cutout and the top of the gooseneck fitting?
C&C 27 Mk IV