It is certainly possible, though not simple, to model the hull of a boat using SketchUp. But I'm a bit unclear about your assignment. In what form have you been "given a floorplan", and what are the characteristics of the space you are supposed to design? As Dave says, the shape of a boat is usually quite complex compared to a house, with few rectangular rooms and few flat or vertical surfaces. By "design", do you mean to plan the layout and materials for the interior furnishings the way an interior designer would do for a house? There are also special considerations that have to be given to materials and design to allow for the damp and sometimes actively wet conditions in a boat. Do you have background for this? If not, you have a lot to learn about boats before you need to worry about SketchUp!