A sound-structure interaction model is established to study the vibro-acoustic characteristics of a semi-submerged cylindrical shell using the wave propagation approach (WPA). The fluid free surface effect is taken into account by satisfying the sound pressure release condition. Then, the far-field sound pressure is predicted with shell's vibration response using the stationary phase method. Modal coupling effect arises due to the existence of fluid free surface. New approaches, diagonal coupling acoustic radiation model (DCARM) and column coupling acoustic radiation model (CCARM) are proposed to handle this problem. New approaches are approved to be able to deal with the modal coupling problem efficiently with a good accuracy at significantly reduced computational cost. Numerical results also indicate that the sound radiation characteristics of a semi-submerged cylindrical shell are quite different from those from the shell fully immersed in fluid. But the far-field sound pressure of a semi-submerged shell fluctuates around that from the shell ideally immersed in fluid. These new approaches can also be used to study the vibro-acoustic problems of cylindrical shells partially coupled with fluid.