My boards racks have always slipped downward when hitting heavy waves and I just can't keep them in the up position. I have tried rubber inner tubes, double sticky tape? The hex bolts are so tight that they are just about to be stripped out, but I just can't get them tight enough to quite slipping. They are Mako/boardracks with aluminium c-style clamps with plastic spacer and hex bolts. I'm going to shoot the off my tower if you can't help me. Thanks. Jet