Tween Surface 3 to one surface

Good afternoon,
For my graduation paper, I am developing an aerodynamic boat, for which the lower part has to remain flat. To decrease drag, I am looking to design a round nose, which blends to the flat part of the boat.
The rear part of the boat consists of 3 surfaces, vertical, horizontal and a blend. The nose consists of 1 surface. I am having trouble blending these surfaces together. The pictures provided show that there is a bump forming. I am forming the surface using tween curve from Pufferfish and also providing a guidance curve by blend curve through a point. Do you have any suggestions on how to improve this approach. Thank you already,

With kind regards,


3. Attach minimal versions of all the relevant files

Hi Joseph,

Thanks for your fast reply. You can find the dedicated files attached here.Rhino_Forum.3dm (409.6 KB) (8.9 KB)


I’ve drawn a lot of boat hulls and there are many considerations… displacement, prismatic coefficient, wetted surface area, etc. Drawing a hull in sections as you are doing is even more difficult because all adjacent surfaces must be tangent and fair to each other.

The best I could do with your model is to ignore the middle section curve (the BlendCPt output) and use Sweep2: (12.8 KB)

Not a good boat!!