Hi!
Although I don't do it very often, I have weathered the ships with Runoff from deck relief ports and other places. Always with an eye toward less not more, Even Shell Tankers used fresh water washdowns at times.
Rust was minimal at best because a well maintained ship or other steel vessel would have work done constantly in the war on rust! The runoff was and is some rather streaky whitish stains down the hull sides. Usually at an angle as they mimiced the path of the ship moving forward in the salt water. In many ships today you only see a ghosting if this phenomina.