No disadvantages to the loose footed sail.
I respectfully disagree with any analysis that says switching from footed to loose-footed sails is highly likely to cause a boom to buckle (all other things being equal).
The forces on the boom aren't significantly different whether the sail is loose footed or not.
If a boom is strong enough to be used with a footed sail, it's strong enough for a loose footed sail. If it's strong enough for mid-boom sheeting with a footed sail, it will be strong enough for mid-boom sheeting with a loose footed sail.
(Please note that I did not claim that it is safe to change a boom from end-boom sheeting to mid-boom sheeting)
Image 1 Below: Orientation of the load bearing paths on a membrane mainsail:
First, the majority of the loading in a mainsail is from the clew to the head along the leach. That doesn't change whether the sail is loose footed or not.
Secondly, regarding the loads along the foot of a mainsail: the load path near the foot goes from the clew horizontally to the tack. There is virtually no vertical load on the sailcloth in the middle of the foot of the sail. The load at the very edge of the foot is 99% horizontal. To put it another way, any sailcloth in the foot which is attached to the middle of the boom is just going along for the ride in terms of vertical loads.
To make my point anecdotally : I'd like to point out that "more expensive" footed sails used to have a baggy foot shelf that is made made from very light cloth, sometimes even from nylon. People did it all the time and nobody every attributed failure of the boom to a shelf. Booms fail for lots of reasons, but not because a racer added a foot shelf to it.
When we design a membrane sail, we align the load bearing fibers in arcs pointing at the three corners, which means the fibers are horizontal at the foot. In like manner, when we design a tri-radial panelled sail, we align the panels with the load bearing fibers pointing at the three corners of the sail; the load bearing fibers are predominantly oriented horizonally at the edge of the foot.
Judy B
Hyde Sails Direct
www.HydeSailsDirect.com
Image 2: A membrane sail, showing the load bearing fibers (below)
Image 3: A tri-radial sail, showing the alignment of the panels to the load paths. The alignment of warp fibers is parallel to the loads in the sail and this is why tri-radial sails have more stable shapes than cross cut sails and also why they respond more predictably to subtle trim adjustments than crosscut sails.
Image 5: This video shows an overview of the computational finite element analysis and load modelling for the fiber layout of a membrane sail, compressed into about 60 seconds!!
