The hydrodynamic aspects of a design study of a TLP type offloading platform, that will operate in the north-east of Marmara Sea are presented in this paper. The main scope of the paper is to discuss the general properties of the platform and environmental conditions prior to the calculation of hydrodynamic forces based on Morison's equation and the resultant motion responses. The non-linear quasi-static effect is taken into account due to set-down phenomenon in the calculation of surge responses. Comparisons between the designs with two different drafts and the results of their spectral analysis are presented. With decrease in the draft of the platform, surge responses increase in the low frequency region. Since the differences between the surge responses of two different designs are not significant, the shorter platform has been adopted for the location due to its low cost. The non-linear set-down effect is not found to be significant because this platform has relatively short taut chains compared to those of conventional type. (C) 2002 Elsevier Science Ltd. All rights reserved.