I have some problems with iges surfaces. I create my models from rhinoceros 5, as you all know we cannot import what we created in rhinoceros, we need to trim some of surfaces in maxsurf then obtain the hydrotatically true model from it. In my iges model, i have skeg, hull surface and appendages (propeler, stern tubes and rudder shaft). When i trim surfaces and create what i desired in maxsurf, i crosscheck my underwater volume both rhinoceros and maxsurf. Rhinoceros gives me a stable result, but in maxsurf i cannot obtain what i expect to obtain. The underwater volume in given draft is always changing. When i untrim the skeg it changes, when i change the surface presicion it changes. Rhino and maxsurf never synchronises. My question is, how can i solve this problem, i need to learn what type of method maxsurf uses to calculate the underwater volume ?