Modern Ships by Sail Assist

[BigV]

xoB, I think you're making an unfair comparison about the raw square footage of the two different examples of sails. The kites in this example are designed to act as airfoils. The lift generated by the air flowing over the shape of the inflated kite is what the boat perceives as thrust/pull.

That's not directly proportional to the thrust provided by the much flatter sails of the Beluga. At 109 meters long that's longer that a 747 by about 40 meters. The 747 has about 5500 square feet of wing area and it can literally fly. Plus, the wind speed at altitude is higher than the wind speed at the surface, usually.

All I'm trying to say is the sail design works more like a wing than a parachute. The performance of the two different shapes is vastly different for a given sail area.