Hi
You shuld consider IntelliCAD that offer a free-download eval. version.
------ This is a 99. pct. AutoCAD clone , it offer all the calculations
you need but, to do these you must know the calculations or the program
; in Lisp you can write applications that is not covered in the various
functions but most are, such as section and volume calculations.
Sad thing is that the free version don't offer Solids, but besidt that
IntelliCAD is a splendid program it even let you open Cyber-Boat plans
and models.

Look for eval. version at ;
http://www.cadopia.com/