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New Material to Decrease Ships' Hull Friction

June 10, 1997

Water beads right up on the highly repellent coating. (Photo: Mitsui Engineering and Shipbuidling Co.)

A major Japanese shipmaker has developed a new, highly water-repellent material. When applied to the hull of a boat, this material reduces by half the friction between the boat and the water, leading to a 20% to 30% increase in fuel efficiency. The manufacturer expects to bring the new repellent into use in four or five years.

Like Water off a Duck's Back
The material, which can be sprayed onto a surface, is composed mainly of fine particles of silica (silicon dioxide) that are chemically engineered to repel water. The water repellency of the material is so high that when an object to which it has been applied is placed in water a thin (2 to 3 mm) layer of air forms between the object and the water.

When a boat whose hull has been treated with this material moves through the water, however, this friction-reducing layer of air breaks up and is washed away. To prevent this, the company designed a system where an onboard compressor toward the ship's bow constantly delivers air to this pocket, maintaining the layer of air and its friction-reducing properties.

The shipmaker calculates that friction between the hull of a standard freighter and the water provides around 60% of the resistance faced by the ship as it sails. If this friction, the greatest source of resistance to the boat, is halved, the overall resistance will drop by 30%, resulting in a matching 30% jump in fuel efficiency.

The maker is currently carrying out resistance tests using flat surfaces; it expects to move on to sea testing involving real boats in two to three years. The durability of the material is also being worked on; the company is confident that it can bring it up to a level allowing actual use by the beginning of the new century. The maker also hopes to keep the price of this new material to within 10% to 20% higher than ordinary hull coatings, making it a good choice for the ships of the future.

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