Identification of the dynamics model of a boat is considered. The requirements of inland waterways are taken into account. Models of motion direction dynamics and translational velocity are studied. Transfer functions from rudder control to motion direction angle and from throttle value to translational velocity are identified by a finite-frequency approach, where sinusoidal test signals are used. A 3 DOF nonlinear model of the boat dynamics is identified via a tool for greybox parameters estimation.