Freeship, Archimedes and Hexagon (polygon modeler), the last one could be little bit tricky to use for an amateur, but for the cost and what it does i think is a good way to go.
Or skip Hexagon go to the magazine store and look for computer arts magazine i think there is a free version of a render and modeler software, to start nothing beats free!.
You can use freeship to start designing your hull and using archimedes to check basic stability, and i added hexagon becouse you can use it to model the rest of your boat, like the house and more.
Please whatever you do, do not ask for a "do it all" sofwtare...... : )
Now if you think to invest some money, then download Rhino and TouchCAD and go from there.
Good luck