You know if there is a free surface here if I what I mean if I take a semi circle, if I oscillate this side at a very high frequency, then it turns out added mass is equal to this. This is a theoretical solution obtained. In fact, if you take any cross section, a good approximation of added mass becomes the mass of that circumscribed semi circle. That is a good approximation, when you have no knowledge you can always use that. Of course, this is only one value and this is valid strictly speaking close to deep water, deep water meaning infinite fluid at high frequency like that. There is a whole lot of discussion on that, we probably cannot go through.