Boat Speed: Salt versus Fresh Water ```Name: Cody Status: Student Grade: 6-8 Location: FL Country: United States Date: Fall 2009 ``` Question: Do boats travel faster in saltwater or fresh water, and why? Replies: There are a number of factors that MAY come into play; however, I doubt that they would overwhelm other factors. First, and most importantly, you did not say "What kind of boat?" -- sailboat, racing skiff, motor boat, etc. I am not using this to criticize you, but rather to illustrate a point. Think about "the problem" or "question" such as you proposed, I have a suggestion. In a quiet (dark) room, sit down in a comfortable chair and "run" the experiment over and over in your head. Pencil paper in hand. Eyes closed --let you mind run free. Scribble key words that you can refer to later, but do not get distracted "taking notes", just key words. This part of the scientific method is seldom if ever taught in school. It takes some practice to become skilled in this technique, but if you let your mind run free not thinking about the problem, while thinking about the problem, ideas may come to you as you re-run the mental DVD. Example: If the boat is sinking, it is not going to go anywhere very fast. So how deep the boat rests in the water will have a big effect regardless of the type of water. Where does that thought lead you? If "deep" is bad maybe "shallow" is good. So for maximum speed you want the boat to float like a cork -- right up in the surface. Yes, but there is a limit. What is that limit? Keep going. With regard to fresh versus salt water. Salt water is more dense than fresh water, so a boat is more likely to float more easily in salt water, but there are so many factors involved it is difficult, without carefully controlled experiments to distinguish the difference (I think). Vince Calder Hi Cody, The only thing that could affect the speed of a boat in salt water, compared to running in fresh water, is that the slightly increased buoyancy of salt water would make the boat float a little higher. This means that there would be less of the boat's hull in the water, and result in a little less "drag" underway. As a result the boat may be able to go slightly (and I do mean only slightly) faster in salt water, then in fresh water. In reality, the difference would be nearly insignificant. Regards, Bob Wilson Click here to return to the Engineering Archives

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