Hi All!
Again you guys are very correct. I cannot imagine running the sub in a stream, only a lake, pond, or swimming pool with still waters. In aircraft there are two measurements of speed, IAS (indicated air speed) and TAS (true air speed). IAS is the speed weather into the wind or with the wind while TAS is the speed over the ground as if you were a car. In this case we can realistically only work with IAS as far as I know.

Best, Ed