

Rotor ships, aka Flettner ships - TeMPOraL
http://en.wikipedia.org/wiki/Rotor_ship

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agapean
Following the links, I find the rotor 'wing' to be more fascinating!

edit: oops! link: <http://www.icar-101.com/icar/index.php>

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Semiapies
It's a fun idea, but I'd be more fascinated if they actually had so much as
small, radio-controlled model that flew and offered any basis for thinking
this wouldn't be just a really inefficient way to build a helicopter.

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Sniffnoy
I notice the article fails to mention the basic disadvantage of this design. A
sailing ship needs wind, a powered ship needs fuel... this needs both!

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secretasiandan
In the article, there's a link to an article of what appears to be a modern
day production version, combining conventional ship propulsion with a Flettner
drive.

<http://en.wikipedia.org/wiki/E-Ship_1>

It looks like it takes advantage of the fact that conventional ship propulsion
still needs fuel and HAS wind if under way (and not travelling such that its
velocity relative to its surrounding airmass is zero).

The article suggests that combining standard ship propulsion with the Flettner
rotors saves fuel : "The Flettner drive allows for projected fuel savings of
30-40% at a speed of 16 knots."

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gvb
The "wind" caused by the ship's forward movement is not useful (it would be
perpetual motion if it were).

The motion of a ship shifts the apparent wind forward (it is a vector addition
of the wind's velocity vector and the ship's velocity vector). The faster a
ship goes, the less useful the _real_ wind will be since the apparent wind
shifts forward, making the "sails" less efficient. The Wikipedia article had
an anecdote that the Flettner rotors worked to 20-30 degrees from dead ahead.
That is pretty good for a sailing ship of 1924 vintage, but still leaves large
angles where the wind is not useful. It also didn't say how efficient the
rotor was at 20 degrees apparent wind. :-O

Obviously, a Flettner rotor sailing ship is vulnerable to all the problems of
a traditional sailing vessel: wind is unreliable (except in the trades) and
often comes from a direction that is not useful (astern, forward). Note that
the trade winds are east/west and a ship generally wants to go east or west to
cross the ocean. Square rigger ships like to sail downwind. Flettner rotors,
not at all.

