Okay. Btw those black lines appear from the IGES. Yes I'm sorry, my bad :) . but my first model which is the symmetric cat seems ok, probably. I...
I think there are too many points in that model considering that I just selected all of the object while exporting.
I make that model from Rhino.
However, does the same way can be done if the catamaran has asymmetric hull? Or we create the mesh manually? Thanks