Wave energy converters (WECs) extract energy from the motion of ocean waves. A variety of different WEC devices have been studied over the past several decades, with emphasis on cost-effective energy extraction. Active control has been shown to improve energy production significantly. Here we investigate energy extraction potential of a tethered heaving cylinder WEC using direct transcription (DT), an open-loop optimal control strategy. This enables direct inclusion of asymmetric constraints on power and tether force, practical considerations not considered in previous studies, and opens the door to WEC optimal control problems with more realistic nonlinear models and integration of control design with physical system design.