Non-stationary model of perturbed dynamics of a rectangular raft on a calm water

There is proposed a full mathematical model for spatial non-stationary motion of the raft of the rectangular form under the action of active forces, of Archimedean forces and resistance forces of water from movement. The force of water resistance in addition to the summand that takes into account the viscosity, contains a summand proportional to the square of the velocity and directed opposite to the velocity vector. Under the assumption that under the action of all the forces the raft remains afloat, there is studied the stability of a first approximation relatively of the steady motions which are arising due to the application of mostly simple active forces.