Modern Wind Propulsion

(Larry G) #1

Seems worthwhile to have a topic dedicated to it. There have been various proposals in this forum and the old one, but they are scattered about.

Things that would be appropriate ti this topic:

Traditional sails
Sky sails/Kite Sails
Rotor Sails
Hybrid wind generation driving electric props?

Stationary Sailboat Configuration
(Larry G) #2

(Larry G) #3

"Maximum rotation speed is low 40-80 RPM depending on diameter.
Operating parameters are vessel course and speed, wind direction and velocity, rotor RPM and generated thrust. The variables are monitored and the system is operated automatically by a microprocessor control module located in the wheelhouse. No specialized crew is required.


Suited for a 30,000 to 40,000 dwt Bulk Carrier or Tanker.

Cruise speed: 14 knots

Wind speed m/s 5 10 15 20 25 30 60
Knots 9.7 19.4 29.1 38.9 48.6 58.3 116
Rotor RPM 30 60 60 60 50 43
Thrust tons 6 24 40 51 52 51
Power KW 430 1700 2900 3700 3700 3650
HP 585 2300 3900 5000 5000 4900

About 50 KW of electric power is required to spin the Monorotor.

Effect of Wind Direction

Wind Angle (degrees) 30 45 60 75 90 105 120 135 150
Power % 10 35 59 77 91 99 100 94 82

The rotor is designed to rotate at maximum of 60 RPM. The table above shows how the thrust can be kept within the 55 ton design limit by adjusting the rotor RPM. Thrust is monitored by strain gauges located on the central support at the point of maximum stress. A PLC program continuously adjusts and maintains the Monorotor RPM within safe limits while maximizing thrust. The program also monitors wind speed and angle of roll in order to stop and park the rotor in extreme weather. No specialized crew is required to operate the system.

When evaluating the performance of the rotor system it is important to keep in mind that it contributes thrust and propulsion horsepower. On the other hand, when calculating propulsion horsepower of a marine engine, its rated power must be adjusted for propeller efficiency (0.65-0.70). For example: 2,000 Monorotor horsepower equals about 2,900 engine brake horsepower.

Many owners are looking at solar collectors to supplement the electric power on board. However, dependent on the trade, panels tend to dirty up and often suffer damage due to weather and crew activities.

The top surface of Monorotors, located high above decks and holds is an ideal platform for solar power generation. P/V solar panels installed flat on the 18 meter diameter top surface of a model 16/22 Monorotor may contribute 20-25 kW during daylight hours. The DC power is routed down through the rotor center and on to a DC/AC inverter via a brush and slip ring assembly. Offered as an option under the patent pending Monorotor system.

Aspect Ratio: (Rotor height/diameter)

Experiments indicate that when comparing the thrust of two Flettner rotors of different heights but with the same projected area and rotating at the same spin ratio, the efficiency of the taller and slimmer rotor is higher than that of the shorter and stubbier rotor.

The difference in output is caused by boundary losses due to air flowing from the high pressure to the low pressure zones over the ends of the cylinder. The end areas of the shorter cylinder represent a relatively larger part of the total projected area, causing higher losses and lowering its efficiency. The short circuit of the air stream near the ends can be mitigated by adding larger diameter discs (Boundary effect fences) at the cylinder ends.

Conversely, since the pressure gradients and conditions near the ends of equally tall rotors are the same at similar surface velocities and wind conditions, the efficiency remains the same as well, irrespective of the diameter and aspect ratio."

(Larry G) #4

I could see a station-keeping seastead using a ring of flettner rotors around the outside rim. Particularly if a way can be designed in to use the internal volume of the rotor for something useful, the roughly 200 sq meters of the rotor footprint would not be a lot to sacrifice to gain up to 50 tons of propulsion.

Since the rotors can be spun in either direction to change the lift direction, they could be programmed to work together to maintain orientation as well as directional stability. The amount of fuel or electricity required to spin the rotors is a fraction of what is gained in any kind of wind.

The mast-like effect of the rotor would be useful as well. A sailboat is partly stabilized by the inertia of the mast swinging like and inverted pendulum, slowing roll. A spar design with heave plates, a long foot, and a flettner rotor up top would probably be pretty stable in terms of roll.

(system) closed #5

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(Francis Brunelle) opened #6

(Larry G) #7

Wing sail advances:

(Larry G) #8

(.) #9

I would use the sloop setup for simplicity.


If we are talking about what was coined as a “sailstead” sometime ago, my first choice would be a “solar sail” propulsion.

It would act as a conventional sail and electricity generator. As shown, it would move around 3-4 knt catching wind while generating plenty of electricity to add another 7-9 knt under power.

13 knt FOR FREE, is not bad at all!