My setup has 2 supports - 1 for the mast when lowered (upper support), and a lower support for the boom. The lower support height above deck is ~54.5 inches (where boom would rest) while the upper support is ~73 inches above deck (where the mast when lowered rests). The support post attaches to the existing railing via 2 horizontal sections w/ removable pins (so the entire post can be removed if desired). The post is NOT screwed down to the cabin top.