Thanks for the help everyone.  What I am looking to do is get some sailing shade for our upcoming Bahamas trip this next year.  
  
  We have a full length awning that is great, but is only useful without us using the mainsail. It should be noted that our main is boom-less and sheets to tracks on the boomkin.  We have a dodger and need a bimini aft that is high enough to let the main sheet under it.
  
  I am not sure I want to spend a whole ton of money on it, so I thought I would buy a second hand one and mount it aft.
  
  Thanks for the help with measurements everyone.
  
  rich