Science Buddies: "Ask an Expert"

hello sir,
i m making a boat which can lift tennis sized balls from water surface as well as beneath the surface.i want to maintain a good speed.i am plannig to use gear motors.please suggest whether paddle technique would be a better option or propellers.also please suggest lifting mechanism if you can.
Thank You.
Aniket.

Hi Aniket,

You bring up a good question with your project. Which method of propulsion will be more efficient for your model boat? Without knowing a lot of details about your project it’s difficult to say, however, if you check out the article at the CHaOS Demonstrators webpage at http://www.chaosscience.org.uk/dem/publ ... 7133241988 you may find some information that will help you make your decision.

CHaOS is a student-run society at the University of Cambridge who organize science events throughout the year. The page I direct you to above deals with a boat tug of war they performed in 2004 with a propeller driven boat up against a paddle wheeler. The comments posted there should be helpful. Good luck!

Hi Aniket,

In addition to what fmcwilliams said, a paddle technique might be easier from a technical standpoint because if the shaft is above the water line you wouldn't have as many problems with water leaking in. (I've built a few motorized boats and that what a major problem in all of them.) Could you also give us some more information such as size and the materials used so we can better help you with ideas for the lifting mechanism?

Thanks,
Philip

Leak issues with propeller shafts can be avoided by using a shaft that exits the hull above the water line or placing a channel through a solid piece of solid foam material to provide a water / propeller channel again above the water line. Coming up with an efficient propeller for your engine is more difficult than paddle wheel designs.

Any use of gears will introduce efficiency losses, add weight, and be another thing to break. Keeping it as simple as you can will significantly improve your chances of success.