Modifiying imported shapes in OpenSCAD

Question

Given an STL file, OpenSCAD is able to import it:

import("file.stl");

I can also transform the result. However, when I try to do any openscad commands, the imported shape disappears:

translate([10,0,0])
    import("Boat.stl");
cube(5);

Once the function call is added to any native shape, the boat disappears. Is there any way around this? I am trying to take a shape that has been sliced into pieces in netfabb, and create tabs so the the pieces fit precisely together for gluing.