Offshore triceratops is one of the new generation compliant platforms, whose structural form inherits salient advantages in alleviating environmental loads. Deck is connected to buoyant legs through ball joints, which transfers only translational motion but restrains rotations. As the buoyant legs are taut-moored, dynamic tether tension variations under the wave loads can cause Mathieu-type instability. The present study examines the stability of triceratops through postulated failure case by increasing payload on the deck. Detailed dynamic analyses under wave loads are carried out through numerical modelling of triceratops, while increased payload intuits postulated failure cases. Phase plots are interpreted to assess the stability of the deck and tethers are assessed using Mathieu stability. It is seen from the results that increased payload causes tether instability. In addition, platform was also found to be unstable prior to that of tether instability, under the postulated cases considered for the study. © 2017 Informa UK Limited, trading as Taylor & Francis Group.