Sailing boats like these magnificent racing yachts, cannot take advantage of solar power. They are thoroughbreds, designed to harness only one energy source from nature.

We are advocates of mechanical sailing, using rotary sails (wind turbines). Why is that? When sailing is such a lot of fun and extremely relaxing escapism.

It is because of the need to manually change trim and direction of the vessel, to use winds that are constantly changing, to steer a course (indirectly) to a destination. This is a lot of work on a small boat or yacht, requiring constant vigilance on the crew's part. Now imagine how many able seamen it would take to man one of the tall ships. What would the wages and food bill be - and where would you find all that labour?

It is just not practical, when compared to bunker fuelled diesel engines, where you just point the ship and sit back with a beverage, until it is time to dock.

With a wind turbine, or rotary sail, such considerations are irrelevant. The machine does all the work for you. The Captain just sets the destination on his autopilot, or in the case of an autonomous vessel, instructs the onboard AI. In our case Captain Nemo.

Sailors travel within about 45 degrees of the (true) wind for better speeds, meaning that reaching a windward mark will involve a series of tacks, resulting in a zig-zag course. Although it is possible to sail directly downwind, this angle is typically slower than sailing at an angle downwind, exchanging sailing a greater distance for greater boat speed. The result is that, typically a sailboat also zig-zags downwind in a series of jibes.

Captains of sailing ships that travel around the world, know about ocean gyres and the correlation with dominant wind flows where they rotate clockwise north of the equator and counterclockwise south of the equator. During the era of sail ship navigation, these gyres had a strong impact on navigators and governed trade flows between countries. In order to combat global warming and pollution that cause acid oceans, we need to re-think burning more fossil fuels, in favour of learning how to master the forces of nature, more effectively.

Sailing ships cannot proceed directly into the wind, but often need to go in that direction. Movement is achieved by tacking. If a vessel is sailing on a starboard tack with the wind blowing from the right side and tacks, it will end up on a port tack with the wind blowing from the left side. See the accompanying image; the red arrow indicates the wind direction. This maneuver is frequently used when the desired direction is (nearly) directly into the wind.

In practice, the sails are set at an angle of 45° to the wind for conventional sail ships and the tacking course is kept as short as possible before a new tack is set in.

Tacking from starboard tack to port tack. Wind shown in red. ① on starboard tack, ② turning to windward to begin the tacking maneuver or "preparing to come about", ③ headed into the wind; the sail luffs and loses propulsion, while the vessel makes way on momentum to provide rudder steerage, ④ making way on the new port tack by sheeting in the mainsail, ⑤ on port tack.Relationship between tacking and beating to windward

The relationship between tacking and beating to windward. There is no need to zig-zag with rotary sails. The turbine head changes angle to face into the wind, the boat keeps on course.

TACKING

This maneuver includes changing direction by turning the front of the boat through the wind.

Tacking is sometimes confused with beating to windward, which is a process of beating a course upwind and generally implies (but does not require) actually coming about. In the accompanying figure, the boat is seen to tack three times while beating to windward.

When used without a modifier, the term "tacking" is always synonymous with "coming about"; however, some find it acceptable to say "tack downwind"; i.e., change tack by jibing rather than coming about. Racers often use this maneuver because most modern sailboats (especially larger boats with spinnakers and a variety of staysails) sail substantially faster on a broad reach than when running "dead" downwind. The extra speed gained by zigzagging downwind can more than make up for the extra distance that must be covered. Cruising boats also often tack downwind when the swells are also coming from dead astern (i.e., there is a "following sea"), because of the more stable motion of the hull.

Coming About is defined as: "To go about is to change the course of a ship by tacking. Ready about, or boutship, is the order to prepare for tacking."

Jibing is tacking downwind, or tacking is jibing upwind. Jibing generally increases boat speed, over running goose-winged.

JIBING

This is also another direction changing maneuver, but it works with the opposite effect. It involves turning the stern of the boat against the wind.

sailing to a place to windward takes a lot longer than going downwind. Even if the boat were as fast close hauled to windward as downwind, which is usually not true, the zigzag tacking makes the actual path a lot longer. If you were tacking 60 degrees to each side of the wind that path would be twice the straight line distance. If you could tack 45 degrees to each side the path would be 1.4 times the straight distance, so you can see the value of a boat that is close winded.

Beating is the procedure by which a ship moves on a zig-zag course to make progress directly into the wind (upwind). No sailing vessel can move directly upwind (though that may be the desired direction). Beating allows the vessel to advance indirectly upwind.

ARCHINAUTE: A rotary sail catamaran was under construction at the Brittany South shipyard in Belz in 2019.

This is a culmination of years of effort for its designer, Charles-Henri Viel, who was looking to present it from June 29 to July 10 at the La Mer XXL show in Nantes in 2018. The boat is 11 meters long, 6 wide and weighs 10 tonnes, built of aluminum. A wind turbine 6 m in diameter will be placed on the boat.

Unthinkable ten years ago, the project finally came to fruition. The transition from idea to design did not happen overnight. In 2014, the first investigations were carried out on a model. Two years later, Charles-Henri Viel participated in a contest: 'clim action.' The principle of which was to propose projects in harmony with the environment.

A ship that is beating will sail as close to the wind as possible; this position is known as close hauled. In general, the closest angle to the wind that a ship can sail is around 35 to 45 degrees. Some modern yachts can sail very near to the wind, while older ships, especially square-rigged ships, are much worse at it.

Thus when a ship is tacking, it is moving both upwind and across the wind. Crosswind movement is not desired, and may be very much undesirable, if for instance the ship is moving along a narrow channel.

With the advent of the ages of steam and later technologies, we have almost forgotten the role that the Trade Winds in developing our global economy. But they are still there for us. We just need to re-learn how to use them in a modern world reliant on global trade.