A windmill ship, wind energy conversion system ship or wind energy harvester ship propels itself by use of a
wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
to drive a
propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
.
They use
wind power
Wind power or wind energy is mostly the use of wind turbines to electricity generation, generate electricity. Wind power is a popular, sustainable energy, sustainable, renewable energy source that has a much smaller Environmental impact of wi ...
through a mechanical or electrical transmission to the propeller. Where transmission is electric, storage batteries may also be used to allow power generated at one time to be used for propulsion later on.
Windmill ships should not be confused with
rotor ships, which instead rely on the
Magnus effect
The Magnus effect is an observable phenomenon commonly associated with a spinning object moving through a fluid. The path of the spinning object is deflected in a manner not present when the object is not spinning. The deflection can be expl ...
for propulsion.
Points of sail
Equipped with a wind conversion device that can rotate 360° no matter in which direction the ship is heading, a windmill ship can sail in any direction.
* It can move directly upwind, a point of sailing unachievable by other sailing craft. Here a wind turbine powers a water propeller. Because the power produced depends on the apparent wind strength, a large amount of power is transmitted to the propeller. In order to operate efficiently in the typically slow speed through the water, the propeller must be large enough to generate more upwind thrust than the combined downwind force of the wind turbine and the air and water resistances of the ship structure itself.
* With the wind from the side, i.e. on a reach, the wind turbine's thrust pushes the ship sideways, which should therefor have a lateral surface such as a keel in order to reduce leeway. Thus equipped the wind turbine can be also be used in an autogyro mode. That is, no rotary power is transmitted and the wind turbine acts in the same manner as a static sail and the ships's speed could exceed wind speed in the same way as with many other sailing craft.
* Sailing downwind, the apparent wind decreases the more the ship speeds up and at exactly the true wind speed, would drop to zero, so that the wind turbine can generate no power and also no thrust if used in the autogyro mode. Therefor windmill ships are limited to less than wind speed when travelling directly downwind, as with other sailing craft. Theoretically the wind turbine could be used instead as an air propeller and the water propeller as a water turbine. The direction of power is then reversed and such a windmill ship could accelerate through the region of zero apparent wind and exceed the wind speed directly downwind. As this requires both the air and water devices to be constructed differently than usual and extremely low water resistance from the hull, this has not been achieved so far with ships, but has been achieved with land yachts. These travel on wheels which offer very little resistance at high speeds compared to that of even the best hulls through water.
Types
Several types can be made; these include wind-turbine-only ships as well as hybrid ships which store wind power from the turbine when the ship does not need to be propelled. To reduce the energy required to propel the boat, windmill ships are often equipped with low-friction hull designs, such as
multihull
A multihull is a boat or ship with more than one hull, whereas a vessel with a single hull is a monohull. The most common multihulls are catamarans (with two hulls), and trimarans (with three hulls). There are other types, with four or more h ...
s, or they are
hydrofoil
A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...
s. Boats without low-friction hulls or hydrofoils can be equipped with wind turbines, but often the force generated by the turbines alone is not sufficient to propel the craft. In this case, the turbines only provide
supplemental force to conventional sails or other propulsion systems.
At present, research is ongoing and the best types of bladed rotors still need to be determined. For example, high horizontal axis windmills are proven to make the ship less stable. Therefore,
vertical axis wind mills (e.g.,
Savonius turbines) are sometimes preferred. Also, the wind mill needs to be highly durable as marine environments tend to degrade windmills more quickly than what is common on land.
Current ships
Few windmill ships have been built to date; these include:
* Jim Bates' Te whaka
* Lindsay Olen's Thrippence
* Peter Worsley's windmill-driven boat http://www.sailwings.net/rotaryhome.html
* Jim Wilkinson's Revelation 2
*
''Blackbird'' (wind-powered vehicle)
The film ''
Waterworld
''Waterworld'' is a 1995 American post-apocalyptic action film directed by Kevin Reynolds and co-written by Peter Rader and David Twohy. It was based on Rader's original 1986 screenplay and stars Kevin Costner, who also produced it with Charl ...
'' starring
Kevin Costner
Kevin Michael Costner (born January 18, 1955) is an American actor, producer, film director and musician. He has received various accolades, including two Academy Awards, two Golden Globe Awards, a Primetime Emmy Award, and two Screen Actor ...
featured a
trimaran
A trimaran (or double-outrigger) is a multihull boat that comprises a main hull and two smaller outrigger hulls (or "floats") which are attached to the main hull with lateral beams. Most modern trimarans are sailing yachts designed for recreati ...
powered by a vertical-axis
Darrieus wind turbine
The Darrieus wind turbine is a type of vertical axis wind turbine (VAWT) used to generate electricity from wind energy. The turbine consists of a number of curved aerofoil blades mounted on a rotating shaft or framework. The curvature of the bla ...
.
References
{{DEFAULTSORT:Windmill Ship
Marine propulsion
Wind-powered vehicles
Boat types