I can’t figure out how to make blue and green surfaces tangent. I realized that the better option here would be extending blue surface forward and than trimming it with gold surfaces but all my attempts so far failed to produce straight intersection between gold and blue extension. So instead I figured I would try patch layout… only to get stuck again when trying to make both surfaces tangent. Any suggestions are highly appreciated.

I may be missing something but the kink where the edges meet means it is impossible for the blue and green surfaces to be tangent without altering the edges. That is how the basic geometry works, independent of how the surfaces are modeled.

What determines the shape and what are the constraints?

Why are you using single span (Bezier) surfaces instead of a multi-span surface? A multi-span surface would have automatic continuity.

Apologies for my late responding. Got one day cut off, voluntarily, from internet…

Thanks Pascal, still not tangent but with beautiful control point distribution. Do I need V8 for that…?

David, I’m well aware these two surfaces cannot be tangent as it is. This is why I am fishing for fresh ideas. I got stuck.
Bus since you mentioned constraints I went back and did more research. It seems I was wrong about hard transition from flat to raising keel ( btw. what is proper terminology for this feature…? ) Now I believe it was soft ( tangent ) like on image below. This should make my work easier.

I’m using single span as an experiment. Just an early sketch at this point. Would like to find out how effective this method is for designing complex hull forms of old battleships.

Right - you can’t have tangency along the whole edge and the kink, as David pointed out - something has to give - you can have tangent and a reversal on one side or the other, or a bit of each,

David, C method what I was after. The intersection between your extended surface and the stem is almost to perfection. But how do I get to that point ? What are the steps to create extended curves for the keel and stem ? I must be missing something because I can’t reproduce it. And I’m talking your hull not mine. Obviously I need to learn basics…