The near shore oscillating water column (OWC) wave energy plant at Vizhinjam, India had twin 1 m Well's turbines and 1 m linked guide vane impulse turbines as power modules. Performance analysis of the observed records during operation yield significant insight on the dimensioning of the turbine with respect to the caisson. A cycle by cycle analysis of energy capture clearly identifies stalling behavior of the Well's turbine. Similarly, the performance degradation of the linked guide vane due to mechanical problems could be identified. Such analysis is possible as the electrical machine is an induction generator and the moment of inertia of the system is relatively small. It is clear that optimum dimensioning of the turbine is a must with an OWC based wave energy plant. Copyright © 2009 by The International Society of Offshore and Polar Engineers (ISOPE).