Hi, Eric,
Just looking at it, the application appears to make a difference.
The interesting design screw shown has the criteria that it must catch
the flow past it, to ensure that the speed of rotation is directly
proportional to that flow. Hence, no blades. I would assume that it is
faced pointy end first, not dragged by the wires, which would create
turbulence and therefore inaccuracy.
For propulsion, the flow created must have as much volume as possible,
and presumably be as fast as possible, which perhaps does away with the
requirement of proportional accuracy. This would mean that such a screw
is unsuitable for propulsion, as it's own shape restrict the total flow
speed.
Propably why model airplane props can work well on trolling motors.
Just my left-handed way of figuring out why the heck that screw is
shaped like that!
John
1a. Re: Incremental Options
Posted by: "Eric" ewdysar@yahoo.com ewdysar
Date: Fri Jun 17, 2011 8:48 am ((PDT))
While this type of water screw may provide accurate flow measurements,
various groups, including goverments, have spent hundreds of years
refining propellers to push boats around. The familiar bladed propeller
has been proven to be more efficient and effective for propulsion again
and again.
If I remember correctly, the "Turtle" submarine built in 1776 had
hand-powered water screws for propulsion that were very similar to the
photo in the link that you posted. So these aren't really a new idea
that is waiting to be discovered.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, GNHBus@... wrote:
>
> http://commons.wikimedia.org/wiki/File:Dumas_Neyrpic_Current_Meter.JPG
>
> Interesting selection for "screw" on this flow meter
--
http://www.fastmail.fm - Faster than the air-speed velocity of an
unladen european swallow
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