4. Vehicle ordering

In the previous paragraphs, we established a 6-degree-of-freedom model for the marine vehicle. In many applications, for example when controlling a surface vessel, it is not necessary for the vehicle's 6 degrees of freedom to be constrained. In such cases, a simplified model is used in which, for example, roll or elevation are not controlled. The equations are then simplified and some terms can be linearized. In what follows, we will deal with the general case with 6 degrees of freedom, from which it is easy to deduce the minimum model depending on the number of degrees of freedom required for the application.