So, the hull is defined by a set of points which is invariant which does not change with time, if I had a coordinate fixed somewhere on the hull that is important, where on the hull we have not specified anywhere on the hul. As I said this particular point, this say 10 meter (()) you know like (()) say this point is 10 meter after the ship I am say 2 meter above it will always remain so that point is this point here say p point p point here.