Re: Flettner's rotor

Greetings:

Your question is very interesting and rekindled old memories, for as 
a boy in the 1940s & 50s I had a Flettner rotor kite and at that time I 
also read about the Flettner ships. The Web has many pages on Flettner’s 
more famous helicopter work; however, there are a few references to the 
ships. Flettner’s work originated from the “Magnus Effect”. 

The "Magnus Effect" was first noticed in the 17th century in connection 
with inaccuracies when firing cannonballs and was investigated by Heinrich 
Magnus. He developed a theory to account for this. Although it has been 
shown that his theory was not valid, the effect is still known as the 
"Magnus Effect". This effect is responsible for the curved ball 
trajectories observed in baseball, tennis, golf and other sports. The 
dimples in golf balls interact with the Magnus effect to extend the 
distance of the ball’s trajectory.

Flettners ships are briefly discussed in the following web pages which 
discuss using rotors in the water for fishing purposes rather than in the 
air. There are many illustrations of the under sea devices on the web 
pages.

http://users.iafrica.com/m/ms/mshenker/ATS8.HTM

QUOTE : Depth Control System for Midwater Trawls 

The Magnus Effect and other Rotor Devices


Flettner's Rotor Ships 

In his search for a "simple and more efficient way of using the free wind 
power available", Anton Flettner came up with the idea of using the Magnus 
Effect. In 1926, the three-masted schooner rig on the 52m "Buckau" was 
replaced by two rotors. Each rotor was -18m high and 2,7m in diameter. She 
exceeded all expectations, being faster than before and able to sail much 
closer to the wind. 

Because of this success, the Transportation Department of the German Navy 
ordered the construction of another rotor ship, the "Barbara". She was 92m 
long and fitted with three rotors. Each rotor was 17m high, 4m in diameter 
and driven at 150 rpm by a 27 kW electric motor. The "Barbara" carried 3000 
tons of cargo and a few passengers. She plied between Hamburg and Italy for 
six years.

Flettner Rotors for Fishing Trawlers

In 1965, the Gloucester Exploratory Fishing and Gear Research Base of the 
Bureau of Commercial Fisheries, together with Mt. Auburn Research 
Associates, Inc., of Cambridge, Mass., started a programme of research on 
controllable depth trawl doors. This led to the development of a rotor 
door. 

In view of the apparent advantages of a rotor device in controlling the 
depth, the programme was extended to laboratory studies. Tests at the 
Massachusetts Institute of Technology confirmed the predicted lift 
coefficients and the stability of the design. 

Two operational prototypes were built, with rotors 1m in long and 0,15m in 
diameter, driven at 200 to 1200 rpm. Sea trials aboard the "Rorqual" were 
very successful: at 3,3 knots the net could easily be raised to the surface 
or lowered to more than half the warp length. 

In 1975, a project was started at the Robert Gordon Institute of 
Technology, Aberdeen, to develop a high-speed towed underwater vehicle for 
use in offshore engineering research activities. 

The vehicle consisted of a streamlined body with a rotor 1,4m long and 50mm 
in diameter projecting horizontally from each side. Sea trials confirmed 
the predictions of downforce and stability. 

Thereafter design was started on a larger version capable of being towed at 
12 knots at a depth of 300m.

END QUOTE

David Culp, an avid sailor and naval architect has a web book on “speed 
sailing” in which he concludes that kites are better that Flettener rotors 
for commercial ships. In one of Culp’s references he lists a Flettner sail 
boat in the 1980s; however, I have not been able to find any more detail 
about it in the following web pages.

http://www.kiteship.com/kites_change.htm

QUOTE:
Speed Sailing: How Can Kites Change This
by David Culp

Kite rigs (free-flying kites) have several inherent advantages over 
conventional sail, plus some distinct limitations.

A strong advantage of kite rigs is that since the rig isn't actually on the 
ship, minimum retrofit, and minimum deck and storage space are required 
(4,5,6). This is particularly  important while at dockside,
when deck space is fully utilized. Wing masts, Flettner rotors, etc. are 
prone to damage or are a hindrance to cargo loading/unloading.

In addition, the kite rig is substantially manufactured away from the 
vessel. Downtime and retrofit costs are minimal. Further, a kite rig can be 
carried from one ship to  another, as for varied testing, or as vessels 
change routes, or owners.

Kites fly at higher altitudes than conventional rigs. Wind velocities 
increase with altitude above the water. A large kite flying at an altitude 
of 1000 ft. will typically see  winds of 15-30% higher
velocity than a conventional rig whose center of effort is 60-80 ft. above 
the water (7,10)). As energy derived from the wind varies with the square 
of its velocity, this  translates to 30-50% more energy available to the 
kite, on a per sq. ft. basis.

END QUOTE

Culp's book then goes into extensive cost modeling for kiteships

Best Regards from Your Mad Scientist
Adrian Popa