Maritime smugglers will often hide contraband in false hulls or propeller shafts within their boats. While there are ways in which port authorities can search for such stashes, the smugglers often have time to ditch their illicit goods before those searches can be performed. However, what if there were stealthy, inexpensive, underwater hull-hugging robots that could check the boats out, without the crews even knowing they were there? That's just what a team at MIT is developing.
The current prototype robot was designed by mechanical engineering grad student Sampriti Bhattacharyya and her advisor, Prof. Harry Asada. Built mainly using a 3D printer, it's oval in shape (but with a flat bottom), and is described as being a little smaller than a football.
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Half of its body is watertight, and contains its electronics – these include its control circuitry, rechargeable lithium battery, communications antenna, and inertial measurement unit. The latter is made up of three accelerometers and three gyroscopes, and is used to keep track of the robot's positioning as determined by its movements.
The other half, which is permeable, houses its propulsion system – this consists of six pumps that are each hooked up to a separate rubber output tube. Two of those tubes come out the back of the robot, pushing it in against the boat's hull as they vent water. The other two pairs are located at either end of the robot, pushing it forward or backward along the hull at a maximum speed of about one meter (3.3 ft) per second, and allowing it to make tight turns.
Although the prototype presently doesn't contain one, Bhattacharyya envisions the robots ultimately being equipped with ultrasound scanners. Fleets of them could be surreptitiously placed on the hulls of suspect vessels, where they would slide along the metal, checking for anomalous readings that might indicate hidden cargo underneath.
Using their communications systems, they could both coordinate their search patterns with one another, and transmit their readings to topside authorities. They would reportedly not produce a wake that might alert crew members to their presence, and could also be camouflaged using clumps of algae.
The prototype is able to run for about 40 minutes on one charge of its battery, although Sampriti plans on increasing that to 100 in the next version. One challenge, however, will involve finding a way of getting good-quality ultrasound readings while moving across the uneven, barnacle- and rivet-festooned hulls. Traditionally, ultrasound only works when maintaining contact with a smooth surface, or when the scanning distance is kept consistent. This could be overcome by establishing a hydrodynamic buffer – a sort of cushion of water – between the robot and the hull surface.
In any case, Bhattacharyya hopes that the final model will be relatively inexpensive – perhaps about US$600 – so that the technology proves more cost-effective than the use of existing underwater robots.