To close out the week we talk about the natural source of wind power. Although rafts and dugout canoes have been around for 12000 years sails were not used until 3000 BC. These were first used by the Chinese, Arabs began using sails around 2000 BC.

Wind powered ships predominantly use sails for their propulsion. However sails are not the only wind powered devices to be used on ships. Airfoils have been used to power sailboats for many years. An airfoil is basically a wing and is mounted vertically on a sailboat. It works just like the wing on an aircraft. A low pressure system develops on one side of the airfoil and a high pressure system on the other. Pressures travel from high to low, this creates lift, or a pushing force. The sailboat is then pushed through the water. US Patent 4708075 is for a multi-hulled sailboat with fixed airfoils.

Another type of wind power is the turbosail, developed by Jacques-Yves Cousteau used on his ship, Alcyone. This system was intended to supplement the ship engines and claimed to improve efficiency by 1/3 onboard Alcyone. Here is how the system works.

It consists of an airfoil, vertical and grossly ovoidal tube, with a mobile flap which improves the separation between the intrados and extrados. An aspiration system pulls air into the tubes, and is used to create an important depression on one side of the sail; propulsion occurs perpendicularly to the pressure. In this way, the "sails" act as wings, with air moving slower on one side, creating drag. Standard engines can then be used in conjunction with the turbosails. These in turn can be coordinated with computers to control the angles, suction power, and rotation of the sails. – from Wikipedia.

However these two systems are not nearly as popular or widely used as the sail. Sails come in many sizes, and shape. Even the simplest sail is made up of different parts. Whole classes, or types, of sailing craft are known by their sails. So over the next few days we will learn the different types of sails and in turn masts that make up a sailing boat/ship.