- The vortex induced motion of structures in the ocean is a broad area of intense research. This study focuses upon the analysis of data from an experimental investigation of a towed instrumented catenary cylinder that was intended to represent a steel catenary riser. The data that was collected at ten equally spaced locations along the catenary included in-line and transverse are characterized in terms of statistical parameters, extremes and mode shape. The extreme motion response at selected elevations is presented in terms of probability of exceedance graphs that provide a comparison of Gaussian and Weibull distribution models with the measured data. 2005 WIT Press.