Pull

Ever measured the pull on your kite line ???   I think you would be surprised.
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Here are the parameters:

1. Gusty wind up to 45km/h  
2. Rokkaku kite was 1,3m²
3. Line thickness: 2 mm

We never got a pull force over10 kg.... although everybody was expecting 20 and more kg....

Nighthawk delta kite

The Nighthawk Delta kite is constructed from top quality sailcloth and fitted with a carbon fibre centre spar and fibreglass wing spars. It has a wooden cross spar for safety. The Nighthawk is designed in New Zealand for fishing but can be used in strong wind for KAP.  For more info:  Paul's fishing kites. The PFK delta doesn't have a spreader out of just wood. The wood in this case is Tawa, some wood that is unique for New Zealand. See: http://en.wikipedia.org/wiki/Tawa_%28tree%29.

According to Pauls Fishing kite site:
Wind range; 5-40 knots (10-75km/h)
Wingspan: 2,1 meter
Minimal kiteline: 50kg B/S
Spreader size:  86 cm (This is not a fixed number: It can vary kite by kite. So before cutting the standard length of 100cm down to desired length, try to stretch the kite sail without hurting the fabric)

Some tuning tips from the manufacturer 
Some technical details gathered by Pierre Lesage
Oostende 100m high at 45km/h