There is indeed a method of developing curved surfaces, but in your case, much easier to do as advised, and wrap a sheet around and mark.
Basically, for a curved surface similar to the one in the photo, the development needs to be done perpendicular to the wall on the elevation. This will give you the top & bottom curves, assuming the angle to the vertical is constant.Developing curved surfaces manually is a real art, especially if the slope angle changes. If you want to persist drawing it manually, I suggest getting a suitable book on the subject and practice for a day or two.
However, you could build a fair amount of boat in a day or two using the paper wrap method.