Still not sure what the moment curves are trying to do. When you do stability the old way you take the centroid of the area of the immersed section and then take a moment from the center of gravity. After you have done this for each station you combine the moments and solve the equasion for an overall righting moment. What puzzles me in the layout of these particular moments curves is why some are on one side of the reference line
while others are on the other.
Area curves are very common on old hand drawn lines
plans. They are usually see originating at station 0 below the centerline in the plan view. In that case they will overlap the diagonals. It really does not matter what reference line
you use for them. I have some but I can't quite seem to manipulate the image so I can reproduce it here with any clarity. I'll try again.
If you have WORHTY OF THE SEA, the K Aage Nielsen story, go to pages 49, or 190. On other lines
drawings it apears that the curve has been drawn and then erased.
If you have my book go to pages 138, 89, 198.
If you have SENSIBLE CRUISING DESIGNS by Herreshoff look at page 273 and 284.
If you have PHILLIP L. RHODES go to page 103.
If you don't have any of those books, shame on you! Buy mine at least.
As I said before, a designer does not need to see that curve. The designer just needs the number. If you are taking areas with a planimeter the curve will show you immediately if one of yout planimeter readings is off.
However, for some designers the area curve is critical to the design process. Laurie Davidson once told he he designed backwards from the area curve. In this case the designer knows what percentage of the total volume he wants at each station. He draws an area curve to conform to that distribution of volume and then shapes the sections and rest of the lines to achieve that curve. I'm not sure Laurie actually worked that way. He may have been messing with me. I also heard that Freres designed that way. I kept the area curve of the Nordic 44 in my computer reference library so that when I desifned a new boat I could compare the area curve to that of the Nordic 44. I really liked the way the 44 sailed and behaved. I never tried to duplicate the N44 curve but I wanted to see how the new boat compared to the N44 as a benchmark.