Hi Michael, stl files with high resolution are the condition for best possible smooth surfaces.
For this Skeinforge is hardly suitable because it generates larger curves rough and irregular, this looks like a basketwork.
However, I don't know why you run Sketchup, in principle there is no need. But Skeinforge has another annoying disadvantage: It can't make various bottom layer and top layer. The back hull for instance, need seven 0,3mm bottom layers = 2.1mm and no top layer.