I was just shecking random forums when I found this.
I'm not an english native speaker but as I understand you are confused with this
green curve?

This one is in some way a sum of all hypothetic bulkheads edges - or if you want outline of the ship side as seen from bow side. Like this:

So it does not show the deck line.
My advice how to make deck lines for all bulkheads will be: make a curve with big radius like the
red one on my picture.
Then align its center line with center line of bulkheads plan and match its edges with each bulkhead edge. We can assume that deck transverse curvatue is the same everywhere.
Actually someone has told you how to do it...
