Actually, it's not that simple. An attached foot sail is cut with the nature of the attachment considered. A loose foot is cut with no restrictions at the foot. Think about it..... If you simply pull the bolt rope out of the boom.... the sail's foot will still want to pinch in and you might not get a true shape.... however... the only way to see it is to take a look at it unattached. If you examine a loose foot in action... there will be no cupping along the foot.... with an attached foot you may see some cupping because of the sailmaker's accommodation this feature.
In any event, I think you will improve performance... perhaps a sail loft can make a slight adjustment to further improve the converted sails shape along the lower edge.
