For about one month now I am using Rhino for the Mac and this week I encountered some problems. What I am trying to do is to draw a wooden ship, an 18th century Man of War, roughly 46 meters long over the perpendiculars and 13 meters wide. I faired this ship myself on scale 1:1 on the mould loft. After this process the measurements were taken from the floor and I made 2D drawings in AutoCad, profiles of the stations, waterlines, sent lines and verticals. Because it is complicated to draw 3D in AutoCad combined with the fact AutoCad has difficulties with curved lines I decided to look for another Cad program and came across Rhino. I started with drawing the keel, stem and stern and that went without great difficulties. Now it is time to fit in the complete shape of the hull. For that I wanted to create a surface on the basis of the exact measurements from the mould loft. For this I imported the AutoCad drawings into a Rhino file and started to work with them. But soon a problem arose. When you draw a curve by points Rhino deviates from these points to make a fair curve. The picture shows this. The line is waterline 5, 5 meters above the level plane. Since this ship is built with 13 main stations there are 15 points for each waterline: two points for the rabbet and 13 for the stations and for the higher waterlines a point is added for the fashion pieces as is the case with this line.
The difference between the curves is evident. In Rhino the curve falls inward fore and aft. AutoCad does not deviate from the given points, Rhino does. For instance: at station number 1 the difference is 440 mm. which is absolutely unacceptable the more so because the waterline is in reality a fair curve.
Is there a way to correct the curve in Rhino so it fits the given measurements?