Depending on your hull surfaces, you might be able to flatten the panels with a standard Rhino command (if your version of Rhino has this command - 3.0 and 4.0 have it, not sure about earlier releases).

Surfaces > Unroll developable Srf

or UnrollSrf at the command line.

I can't say weather or not its accurate enough for a S-n-G hull, though, I would suspect it is.

In Rhino, I use 2 rail sweeps, lofting, and patching to make the appropriate surfaces, regular lofting and patches don't unroll very well, if at all. But this is for skin on frame hulls, which seem to have a lot of complex things happening where sharp chines blend into surfaces at the bow and stern; S-n-G should be much easier.

I've been trying to export models to FreeShip for the same reason(s) - Michlet.

I've tried some hydrostatics plug-ins for Rhino (trial or demo versions) RhinoMarine being the best of the bunch. However, I was never able to get it to run resistance calculations, but the stability calculations worked great and were helpful in determining how realistic my various kayak ideas might be, and how they compared (theoretically) to manufactured designs on the market (where data is available, anyway).

The built-in hyrdostatics command in Rhino (again, in 3.0 and 4.0, not sure about earlier versions) is helpful for determining displacement, draft, LCB, and wetted surface area.

: No, i still develop panels in Rhino, they arent perfect Rhino isnt the best
: for that but i use them mostly as indication for dimensions, for the panel
: shapes i still use the batten and triangles method, saves tons of times to
: me, no surprises since unless you have a software created for plate
: developement with description of the material etc youll never be sure
: 100%, so why sweat it? they used it for centuries and worked out great so
: its fine for me too. I dont even print full scale, i like lofting, dont
: want to use the computer for everything.

: The reason to work with Freeship its simply for the easy export in michlet,
: for the possibility to create and treat a surface in different ways than
: Rhino does: each software has something that it does better/faster/easier
: than the other so at the end even counting the time of importing/exporting
: its still faster to use more than one thing. And on top of all that there
: are the calculations, costs aside i absolutely refuse to even try the
: marine plugin for Rhino, the company that created it uses a Crypkey
: protection that, beside being a real weak one, is too invasive for my
: tastes, for my activity in boat design/build freeship or michelet
: hydrostatics are more than enough.