I have some questions on sail shape and tuning this particular sail. was hoping someone would watch video and provide some feedback. wind was around 10mph. what is most critical adjustment? (downhaul, etc....) seems to work best when i rig it with a little bag in downhaul and foot. i know its for a sailboat but it seems to work ok. if i were to modify or make a new sail, what design features should be included? thanks.