Drug smuggling via semi-submersible boats

[Skybird]

http://www.spiegel.de/international/...562603,00.html

The boats, made of plastic or steel, can carry up to 10 tons of cocaine each. Because they cannot submerge completely, the correct term for the boats is semi-submersibles. They are used primarily on the drug trafficking routes between Colombia and Guatemala or Mexico. The cartels have devised a complete logistics system, with fishing boats stationed along the way to warn the crews against patrols and provide them with food and water.

The drug boats have to be piloted almost blindly. They sit low in the water, and the crews rely on a type of GPS system used by yachts for navigation. The smugglers spend up to two weeks at sea. They move slowly during the day to avoid creating the telltale wake. But under cover of darkness, they crawl northward at six knots. In 2006, the vessels are believed to have carried between 500 and 700 tons of cocaine from South America toward the United States. About two-thirds of the drugs reached the United States along a western route in the Pacific, while the rest passed through the Caribbean. The number of submersibles is on the rise.

I wonder what subs' sonar can make of them.