No matter how well the furling system works, or how good the torsional rope is, there are still limits. Full-sized broad-reaching and running spinnakers have mid-girths of as much of 100 percent of the foot length and can be very deep. That can be problematic to furl. As a rough guideline, if the mid-girth is much over 88-90 percent of the foot length, all bets are off. It might furl, it might not. That’s when a spinnaker sock makes the most sense. They’re a good choice for full-sized asymmetrical spinnakers designed for broad reaching and running. They are also more cost effective, since a good top-down furling system with a proper torsional rope can easily cost as much as the sail.