I have a Calvert dacron square top for my 5.8. It must be 8 or 10 oz material - weighs a ton. I think the original owner must have asked for a sail that would outlive the boat. It goes like snot in light and medium air , but I have difficulty controling it in heavy air (15 mph +) - that might have more to do with me than the sail design though. In very light air it makes the boat almost unbeatable.