Talk:Windmill ship

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How does this not violate thermodynamics -- that for every action there is an *equal* and opposite reaction. How can you do better than standing still? — Preceding unsigned comment added by 136.159.108.125 (talk) 02:01, 14 November 2012 (UTC)

- It works because of the difference between speed through the air and speed through the water. Power is force x speed, and since (when heading directly into wind) the air speed is less than the water speed, a greater propulsive force can be generated in the water than the drag force on the windmill, for an equal power. It of course only works when there is wind to drive the boat- in calm weather, there is no speed differential and so no net forward thrust. Another way to look at it is that each blade of the wind turbine is tacking into wind. — Preceding unsigned comment added by 2.124.245.53 (talk) 15:49, 8 December 2015 (UTC)

The explanation contains errors. The reason that a windmill boat or ship can travel upwind is that the power conversion of the windmill is greater than the drag of the windmill. However, experience has consistently shown that the power and the drag become equal at a speed directly into the wind when the boat is moving at half of the wind speed. The same speed limit occurs in all directions. This assumes that the windmill is producing its maximum power. To exceed half the speed of the wind, the windmill must operate in a manner to minimize its drag. Doing so usually requires reducing its power. So the goal is to maximize the power to drag ratio. The success of the Blackbird vehicle that sailed directly upwind at about two times the windspeed, and directly downwind at about three times the wind speed, used that technique. But water drag is much higher than for wheels on level ground. So boats cannot or ships cannot use that same technique. However, a new technique has been proposed that might work to enable windmill powered boats to exceed the speed of the wind in all directions. It is called "power alternating sailing" or PAS. In it simplest form, it uses an extremely wide catamaran or trimaran. A vertical axis wind turbine (VAWT) is mounted on each side of the catamaran. Each hull has a propeller that is driven by the opposite VAWT. The technique is to leave the "on" VAWT stationary while the opposite hull swings forward, perhaps on hydrofoils or some other lifting device, through an arc of 90 degrees. Then the opposite, now forward VAWT, is turned on while the other VAWT is turned off. The boat, called a Tazmaran, proceeds forward somewhat like a person walking, with the stationary foot propelling the moving foot. More advanced versions of this PAS technique would use two separate craft, equipped with windmill, that power each other by means of an extremely long and light cord. The craft could be, for example, wings in ground effect craft with only a propeller in the water. The PAS technique was evaluated by a group of engineering professors at a technical university. They concluded that the technique was feasible, at least for two land yachts that take turns powering each other using a long and light cord. A key part of the technique is that the cord must move very rapidly relative to the speed of the moving land yacht. By moving very rapidly, the cord can transmit the most power for the least drag on the moving land yacht when the moving land yacht is ahead of the stationary land yacht. The VAWT proposed to be used by each of the twin land yachts is the Sharp Cycloturbine which has both strong torque and a moderately high tip speed ratio of about four. The inventor of both the Sharp Cycloturbine and the PAS technique is Peter A. Sharp. However, more engineering work is required to optimize the design of the twin land yachts so as to minimize the aerodynamic drag of the "off" VAWT on the moving land yacht by facing the VAWT blades directly into the wind. For more information, contact the inventor at sharpencil at sbcglobal.net. 2601:643:867F:2000:558F:EA13:1AE6:600E (talk) 22:06, 13 October 2025 (UTC)