I own a 21 ft 1974 Macgregor. I'm wanting to buy a new mainsail because mine is plum worn out. I sail at a fairly windy lake. From March to November I would say I sail my boat around 15 to 20 times. I dont race at all. I just enjoy to sailing and have all my life. I like durabilty. I want this sail to last a long time. My question is: what wieght of Dacron do you think is right for my type of boat and sailing?