The ridge length of that Hennessy tarp is 132". That is sufficient to cover an 11 to 12' hammock easily (the ridge length of a properly hung hammock is 80-85% of the hammocks overall length), which would be about 9 feet. As pointed out,that Hennessy tarp hangs as an asymmetric diamond, which gives adequate coverage for sleeping, but not a lot of room to hang out when it is e.g. raining. I have an asym. diamond for hiking, and a Hex for base camping

If you're not sure what will work best for you, make a cheap prototype from 3 mil plastic drop cloth and duct tape. Here are measurments for an asym diamond

http://www.dream-hammock.com/DiamondTarpTutorial.html

and here's a method for plastic sheet, no sew, construction

http://www.youtube.com/watch?v=FgCUc_aUn...mp;feature=plcp

Here's one way to put a fixed ridgeline on a SB Pro

http://www.hammockforums.net/forum/showthread.php?t=5045

this gives a ridge length of 105", which is almost 9 feet, so an 11' tarp ridgeline should be enough.