Paravane

I am trying to make a Kangaroo model of a paravane which is to be used along with a large traction kite, to fly over the water.

...like this : https://www.youtube.com/watch?v=sXpPyWx7JoQ

Up to now, I have been able to simulate it roughly : http://www.box.net/shared/static/f4y9rq68eicjg6ida8oy.avi

I used a pressure component on my two foils (mesh strips).

Just as expected, the foils want to reach the surface, and as soon as they do, a stable position is found.

To simulate this behavior, I cheated by using a CollideSurf component : when mesh faces reach the upper surface of my box (water surface), then they stick to it.

In reality, they should be pulled out of the water by their traction cables, but they should not be affected by pressure anymore.

So how could I simulate this more realistically ?

Ideally, there should be a condition on the pressure, but I'm not sure how to set this up...

Apart from that , I would need my springs to be very stiff because in reality, my lines will not stretch much. But I noticed that setting high values for stiffness results in strange results, and even "explosion" of the model above certain values...

Is that a limitation of the algorithms that are used in kangaroo ?

Oh, and why does my model explodes sometimes when coming in contact with the CollideSrf Brep ?

Cheers,