Yeah, I was just looking at your yacht merge component.gh file and can see the problem, without yet fully grasping the intent… The problem is that Merge can mix up the sequence of inputs (points in this case) due to data trees. You can replace it with Entwine and flatten the output:
Yacht_2022Oct26a.gh (31.2 KB)
For the benefit of others, here is the description you wrote:
Flatten integrates the 2 points far above the hull (those created with coordinates by sliders) but the curve should start at the hull and end at the other tangent while the 2 free points shall control the curvature
So I failed to put the points in the right order.
Sorting them by X Value would be an option?