Windmill ship

Because a windmill can rotate 360° into the wind, no matter what direction the ship is facing, a windmill ship can sail in any direction. In fact, because the power produced depends almost entirely on the apparent wind, they can produce the most power sailing directly upwind.[2][3] Note that sailing upwind, while resulting in more power generation by the wind turbine, requires more power to be expended by the engine and thus it is still more efficient to sail down wind. To sail upwind, a conventional sailing vessel must tack across the wind.

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 multihulls, or they are hydrofoils. 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 still going on and the best types of bladed rotors still needs to be determined. For example, high horizontal axis wind mills are proven to make the ship less stable. Therefore, vertical axis wind mills (e.g., Savonius turbines) are sometimes preferred.[4] Also, the wind mill needs to be highly durable as marine environments tend to degrade windmills more quickly than what is common on land.[5][6]

Few windmill ships have been built to date; these include:[7]

• Jim Bates' Te whaka
• Lindsay Olen's Thrippence
• Peter Worsley's windmill-driven boat
• Jim Wilkinson's Revelation 2[8]
• Blackbird (land yacht)

The film Waterworld starring Kevin Costner featured a trimaran powered by a vertical-axis Darrieus wind turbine.