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Need some understanding of propeller design? Answered

I need some help in understanding the science behind aqua propeller designs.  For example what is the difference between modern outboard motor propeller vs. what they used in steam boats.  To me the steam boat design looks pretty good.  After all it displaces more water.  

I would appreciate the help.

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petercd

4 years ago

The steam boat prop displaces more water, but at a much slower rpm.

High rpm blades like the outboard prop suffer from cavitation above a certain rpm, which can chew the blade up fairly quickly.

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kabirapetercd

Answer 4 years ago

First of all, thanks everyone for the answers.

So, it seems like the Steam Boat propulsion is not so bad a design, other than its large size?

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seandogue

4 years ago

I recommend performing a web search for propeller design.

Erm steam boat propulsion isn't necessarily "bad" persay, (nor is a paddle wheel) but it's traditional sources of power are. "Efficient" really depends on a variety of criteria.

Is it efficient to purchase a forty thousand dollar diesel generator for use in an environment when he citizenry who might benefit from its installation can't afford to buy the fuel? Nope. But that doesn't mean that diesel isn't one of the most efficient internal combustion technologies.

Would I use a propeller designed for an attack submarine to lift water powered by a couple of water buffalo? ...pretty darned unlikely, as it would not be efficient. as a simple Archimedes screw designed for lifting water at low rpm.

get my drift? I can't answer your question regarding efficiency because I don't know enough (rhetorically speaking as I won't be doing detailed analysis) about how you're going to power it and/or use it. All I can say is that it's efficient within a particular frame of reference. Its efficiency in in part measured by its comparison to other technologies, energy sources, designs, costs, etc an it intrinsic worth. (a log that's damp is better than no log at all)

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iceng

4 years ago

As Petercd says cavitation is lost energy and gives away submarine location.

Back in the cold war with Russia, the US developed non-cavitating sub propellers and the special lathes to machine them.

A major Japanese company was hired to use the machines to manufacture these propellers for the US Navy. That turned out to be a stupid mistake as the lathes design was sold to the USSR !