Hi Bob, nice to see you on line, I was going to say that the real RMAS Arrochar, 265ft in length, always trimmed half to one metre by the stern, four blade screw with 3000hp driving her, never steered in a straight line with out using the wheel and always at least 3 degrees of port wheel on. Thank goodness she had automatic steering, but as Bob has just said there are so many different affects on a vessel, which vary all the time, no vessel will even in best trim steer absolutely perfect unlike road vehicles which incidently you should always keep your hands on the steering wheel there as well.