How to cut a surface in n parts ?

Hi Michel

The first thing I did was to do a surface offset at a distance of 0 this makes a copy of your lofted surface

I then edited your sketch 4, used the convert entities command to convert the spline from sketch 3 and joined the 2 splines using 2 lines

I then did a surface trim using sketch 4 as the trim tool and I used the keep selections option to trim away the ends of your lofted surface

This now leaves you with only the middle section of your original loft

I now used the trim surface command to cut away the center section of the surface offset surface that I had created. You are then left with your 3 separate surfaces

Have a look at the attached file

Paul