Forgive me if this has been asked, answered, or is just common knowledge but I am trying to determine the height of my boom as based on the luff length of my mainsails. I have all the measurements I need but am trying to figure in a dimension for how much distance should remain after fully hoisting the main between the halyard sheave and the head of the sail. My boom is on a track so compensating for luff stretch over time will not be an issue, there is also the Cunningham. I just need a "minimum" spec so I can measure for a stern arch and also place the booms track is a centered location. Also, I need to install a sheave at the masthead, when locating one of these is there a distance from the actual masthead you want to maintain? This seems so simple but I am starting from scratch so I don't want to assume anything. THANKS in advance for any help.