This example shows how to create two boundary blends on both sides of the middle curve that are tangent to each other. To impose tangency between two boundary blends, create a Ribbon surface along the middle curve. When defining reference curves for the Ribbon surface, select the three inner curves on both sides of the middle curve.

The Ribbon surface (shown with red boundaries) is now tangent to all the reference curves.

Create the boundary blend on the left side of the middle curve. When defining boundary conditions, specify a tangency condition on the middle curve by referencing the Ribbon surface. Because the Ribbon is tangent to the inner side curves on the right, the boundary blend on the left is now tangent to the curve on the right.

Create the boundary blend on the right and make it tangent to the Ribbon surface.