Because both planar curve curl back on themselves at the front of this submarine, any technique has problems. If I extrude the planar curves so they intersect each other, I get two resulting curves, but neither is correct.

Creating a series of control points, finding the intersection with the other curve requires filtering the double points, but I cant think of a good logic to do that

It works for me. I disabled the parts that rebuild curves and show curvature graphs. One thing to note is that your two guide curves (‘sheer top view’ and ‘sheer profile’ in my model) don’t meet? But the result still looks good.

It matches well in front view but not top view. I think your curves must meet at one end for these methods to work. P.S. Tested - there’s more to it than that…

The second method I posted isn’t really valid except in special cases. I use the first method for boat sheer lines all the time and it works great. Having the curves double back as you do presents a problem. What does this boat look like?

Both these curves, curve back on themselves slightly at the nose. This generates two points that are valid projections an intersecting plane, which appears to be the method common to all these solutions.

That picture is too small to tell me anything but the problem is pretty obvious when you look at it this way, which appears to be what the plugin is doing?