I can't help with Blender as I have never used it.Librecad will allow you to do a 2D lofting and that may be enough to give you a good grounding in the lofting process.Freeship will allow you to input a table of offsets and the X,Y,Z coordinates you have derived may be an excellent starting point.The older versions of Freeship-version 2.6- would allow an IGES file to be exported and maybe Blender could import such a thing.
A knife edge stem may well be outside the class rules as well as being very difficult to build.Furthermore,it would be ridiculously fragile in use.For practical purposes a line at the rake of the stem and offset perhaps 5mm to one side would be a good lofting or surfacing aid.If you wanted to refine the surface or even build the hull,a 4 to 5mm radius wouldn't be too great a task.
