In hydrography the vessel volume is required to determine the stability point for setting up the transducer of echosounder to obtain better accuracy. Volume calculation is also required to determine thickness of sediment for marine engineering. Surface which the volume under it will be determined is generally irregular, so that the volume from the measurements will always have the uncertainty how fit it with the actual volume. This research is objected to find how the vessel volume calculated by Simpson rule can represent the actual volume so that it can be applied to irregular surface area such as land or seabed topography. Half ellipsoid is taken as the vessel ship so it can be compared with the actual. After gridding process then volume is calculated by applying Simpson First Rule. The characteristics which are found will give the consideration in application for irregular surfaces. It is found that the quality of volume representation more determined by how fit the entire surface shape (especially at extremes points) then the grid size. However, the grid size consideration is still required for efficiency in calculation.