Can t join 2 curves, why?

can t join blue and pink curves.3dm (29.8 KB)

You can’t join curves like that in the middle - only at the open ends. (suggest you read the users guide, beginner online tutorials and the like -

What is it you are trying to do?

Hej Helvetosaur.
Tnx for fast answer, yes, I am new in Rhino.
I produce boat covers, so that is one sprayhood construction for sail boat, which I scanned with a camera and processed with Photomodeler software.
Now i’m trying to make a 2d pattern for further production of new boat cover, of course, I did some Rhino courses, but it’s never enough, for example, last project I solved this problem with a line extension and a simple trim, but now it doesn’t work, thank you and of course I’ll study rhino many more times, but if you have some advice, i would appreciate a lot. Big greetings from Sweden

Done, tnx