Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne 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

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory