The Air Lubrication System works on the simple principle of trapping a layer of air bubbles beneath the ship’s hull. An air blower or a dedicated system is used to generate air bubbles to pass them continuously beneath the ship’s surface.
Air bubble outlets are created at different locations along the bottom of the hull, symmetrically on both sides of the ship’s centre line. The air is blown at a constant rate to form a layer of bubbles, which reduces the drag and resistance between the ship and the seawater.
This system continuously replenishes the lost air bubbles ensures that a uniform layer of air bubbles is maintained beneath the ship and the desired effect is produced.
Though a promising technology, the Air Lubrication System has a few concerns regarding its implementation and performance on ships. Some of the main ones are:
- The Air Lubrication System (ALS) until now can only be used for certain types of ships having flat bottoms. Ships having V-shaped hulls, such as certain warships or recreational vessels might not be able to reap the benefits of the air lubrication system.
- To trap the layer of bubbles beneath the ship’s hull is a challenging task. Though solutions such as protruding ridges at the edges of the hull can help in trapping the blanket of bubbles, the sucking effect of the propeller on the bubbles is difficult to defy. Another solution is to design the ship’s stern or hull in such a way that it traps the air bubbles beneath the hull. However, this would substantially increase the building cost of the ship.
- It is also feared that the air cavities made for trapping the air bubbles would affect the handling and stability of the ship at sea. If true this can cause difficulty for the ship and the crew, especially on rough seas.
- The air bubbles leaving the hull surface flow into the ship’s propeller. This can influence the efficiency, noise, and vibration of the propeller. Though according to the experiments conducted by Mitsubishi, there were negligible effects of air bubbles on the propeller, rough seas and changes in fluid density can produce unfavourable results.
- In order to obtain the desired effect, it is important that air bubbles are of uniform size and are evenly distributed beneath the hull surface. Moreover, a change in air bubble diameter would drastically affect the air bubble distribution beneath the hull. An arrangement is, therefore, necessary to ensure that the bubbles are of the same diameter (if possible) and are well distributed beneath the ship’s hull.