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Old 05-09-2012, 09:10 AM
kanicbird kanicbird is offline
Join Date: May 1999
Posts: 18,552
Originally Posted by ralph124c View Post
I know that propellers are very efficient, but what about the big rear paddle wheels?
These were used up to the present day-Mississippi steamers using paddle wheels were made up to the 1930's.
Of course, a river steamship has different requirements from an ocean going ship..and a paddle wheel may be less prone to damage in shallow water.
I don't believe they are that efficient. I did a senior project to construct a underwater vehicle and did some research on props. Typically they are about 50% (about 50% of the engine hp is transferred to the water, the other 50% never is produced by the engine). Also the most efficient prop configuration would be a single blade, though for balance a dual blade is the most efficient practical set up. The more blades the less efficiency though the more power you can transmit so more thrust. The reason for the loss of efficiency for more blades is that the blades are passing through the propwash of the others.

Props can be made more efficient but they are a compromise to operate over a speed range and load range. A variable pitch prop could compensate and deliver higher efficiencies.

With the above posting that a dolphin efficiency at .81 I'd say that nature has a efficiency advantage which may be quite significant. My money is still on the penguin however.