Although in most vessels the usual function of a moonpool is a passage for production lines, equipments and divers, the moonpool may be used as a device to reduce the vertical motion of floating structures as it can be observed in published studies. From these published works one may say that changes of the moonpool’s internal geometry modify the behavior of vertical oscillation of the water inside the moonpool. Looking for a “hydrodynamic design of the monocolumn-moonpool”, Petrobras has carried out a set of numerical and experimental tests with monocolumn hulls provided with moonpool. Some of these results have been published by the authors in the literature. To increase the comprehension of the dynamics of the joint motion, fluid and structure, numerical results were obtained using a commercial code based on the potential theory and a commercial code based on the solution of Navier-Stokes equations. The paper presents results of these experiments and analyzes the behavior of the coupled motions of mono-columns and the vertical motion of the water inside the moonpool, comparing the experimental and the numerical results.Copyright © 2008 by ASME