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Using compressed and high pressurised air to provide a propulsion force to ships isn't a new concept. These types of sailing ships are of a totally different type,i.e they use force of air as the sole propulsion system.For e.g, ships with sails and hover crafts. But there are ships that use compressed air to make their main propulsion system more efficient.
Slippery ships are one such type that use pressurized air to glide over a carpet of air, reducing the drag and friction. This not only increases the speed of the ship but also reduce fuel consumption. It is been predicted that this system will reduce the fuel consumption and carbon dioxide emission by more than 15 %.The best part of this system is that it can be used on any type of ship, from cargo carriers to tankers.
You might be wondering how is it possible to create a layer of air below such heavy ships? The question is valid, but would be more amazed to find that it works other way round here. This means that the bigger the ship, larger the hull and thus more the stability to help maintain the air lubrication layer.As this ships easily slip over the air cushion generated, they are known as slippery ships.
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How Do They Work?
The surface of the ship when in contact with the water produces a turbulent area which reduces the flow of any solid surface in the water. This layer is known as the boundary layer. Due to the presence of this turbulent layer a frictional drag in created between the hull surface and the surrounding water. Efforts are made to reduce the effects of this boundary layer.
Air cavities are made in the subsurface through which air is pumped.The cavities are broad, shallow recesses in the ship's hull. The air pushed through these cavities create buoyant pockets that reduces the drag and help the ship to sail smoothly through the water. When the air is pumped through the cavities, the boundary layer is lubricated which reduces the frictional drag. As the viscosity of air is just 1% of that of water, the air pockets do not move, which creates a stationary air layer for the ship to move over it smoothly. This air pockets are created just millimeters away from the ship's hull, providing a frictionless surface to glide on. It is been proved that the air cavity system reduces the air drag by 7%.
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In order that the system works efficiently, a continuous supply of compressed air is needed. But that only wouldn't assure an efficient system. Rough waves have a tendency to wash away the air layer and just a continuous supply of air wouldn't suffice. The supply of air needs to be altered according to the intensity of waves. For this, the ship is equipped with radars and lasers sensors that measure the oncoming oncoming waves and an automatic air supply system maintains the supply of air in case of rough weather.
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