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.
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.
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.