This study models roll motion response of a barge subjected to beam sea conditions as a single degree of freedom system. The measured wave, either regular or random, is input into a computer program which uses a fourth order Runge Kutta integration method to numerically predict roll motion response. The simulated results are compared to measured data to determine the best system damping parameters. Four different forms of the damping moment of the SDOF model are analyzed. In each form all coefficients are known except for the linear and nonlinear damping parameters. Each form uses a combination of relative motion Morison' damping and/or linear structural damping. Predicted results of the four forms of the damping moment are examined to determine the most suitable model. A sensitivity study on the response to various system parameters is then conducted on the selected form. Each form of the model uses a thirteenth order polynomial restoring moment. An analysis is also conducted to determine the effects of using lower order terms to represent the restoring moment. Finally, results of the SDOF model from this report are compared with a 3DOF and a 2DOF model subjected to the same wave environment to determine which model more accurately predicts roll response.