The Windsled Technique
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.
Generally the bigger kites are the most used ones as it is always optimal for navigation with light winds.
Nasa Kites are very basic, simple, made of one simple cloth, slow, with no foils but have an extreme traction, because all those aspects are the chosen one, as the kite is used normally with 2 lines.
For the extreme traction needed to pull the sled, it is important that the kites are very slow. And that in case to be released from the sled they will not fly away.
The kites can go at different lengths from the sled, from a mínimum of 125 m to a máximum of 500m.
The optimal length being 250 m.
The ropes used are light and extremely strong and have almost no elasticity.
The Windsled cannot go against the wind and just occasionally can go 90º from the wind.
The Kite window in Nasa is small and usually 45º is the most you can go in frontal pull.
There are 2 types of pull, frontal pull and lateral pull.
In order to sail at angles between 45 and 90º, the lateral pull is used, it means that the pulley is dragging the sled from a side not from the centre, and a brake is putted in the opposite side in a way that a variable angle can be earned.
In light sleds of up to 1000 kg is possible to get the sistema up to 90º from the wind, as the weight of the sled increases the angle from the wind you can travel diminishes, in a way that for a 3000 kg sled the máximum angle that can be used will be 60 or 65º from the wind.
On some occasions the winds in altitude can have different direction than the surface wind, it has to be taken into account greatly for navigation.
In fact surface conditions are not especially important, as strength is usually lower and the angle can be different.