If a vehicle is that large, though, it has to have some pretty powerful engines to be able to move at all. Considering we're talking about technology that can produce vast amounts of energy from small devices (like Wren's chest cannon capable of destroying a space station) I think the energy output of a vehicle like the hovercraft could be pretty high.
But my main point was really that we can't judge the size of the world by things like the representation of the vehicles or people on the world map. After all, Chaz doesn't suddenly grow into a giant as tall as Krup or the land rover when he walks outside a town.
