Accurate computation of the drift forces and moments is required to study the higher order steady excitations on the floater in waves. One of the components of the drift forces and moments is regarding the relative wave elevation. To obtain this term, we need an accurate estimation of the wave elevation. If the field point is exactly on the waterline, we will encounter some difficulty to get the potential value.
This paper will provide a more accurate method to calculate the wave elevation around the body and discuss the mathematical justifications. The accuracy will be validated by the comparison against the commercial software. When using more panels in the commercial software, the results will converge to those from our in-house program. We observe a large discrepancy in the relatively higher frequency range. The sharp spikes in the original method are not observed in the improved method. Therefore it is necessary to adopt the proposed method in order to provide more reasonable predictions of the mean drift forces.