On the website:
The Windsled is a sailing boat for the ice, but the technique of sailing is completely different to a traditional sailing boat.
The sleds are dragged by a set of kites that can be as big as 150 sq meters.
For an expedition are normally transported around 20 kites from different sizes. That can be categorized in 3 different ranges.
Small kites. Up to 30 Sq/m. Usually 7,5m, 10 m, 15m, 20m, 25m
Medium kites. From 30 to 70 sq/m. Usually 30m, 40m, 50m, 60m, 70m
Big Kites. From 80 to 150. Usually 80m, 100, 110m, 150m
Giant Kites. More than 150 sq/m.
Unsuccessful attempts have been made using bigger kites, testing kites as big as 250 sq/m but have proven too difficult to handle and not practical.
On the last point, crosswind flying with a 250 m² kite may be difficult to master in the conditions described, but things may be different for static flying requiring little maneuvering.
After all, if a parachute can scale up to 5000 m² and perhaps more, why shouldn’t the same be true for an NPW Rogallo like the one from Windsled?