Although the heaving Point Absorber (PA) concept is well known in wave energy conversion research, few studies focus on appropriate modelling of non-linear fluid viscous and mechanical friction dynamics. Even though these concepts are known to have non-linear effects on the hydrodynamic system, most research studies consider linearity as a starting point and in so doing have a weak approach to modelling the true dynamic behaviour, particularly close to resonance. The sole use of linear modelling leads to limited ability to develop control strategies capable of true power capture optimisation and suitable device operation. Based on a 1/50 scale cylindrical heaving PA, this research focuses on a strategy for hydrodynamic model development and experimental verification. In this study, nonlinear dynamics are considered, including the lumped effect of the fluid viscous and mechanical friction forces. The excellent correspondence between the derived non-linear model and wave tank tested PA behaviours provides a strong background for wave energy tuning and control system design.