An unmanned semi-submersible vehicle developed at Washington State University may prove that the best way to travel in water undetected and efficiently isn’t on top or below, but in-between.
The roughly 45-centimtre-long semi-sub prototype, built with off-the-shelf and 3D-printed parts, showed its seaworthiness in water tests, moving quickly with low drag and a low profile.
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This type of vessel isn’t new. In recent years, crudely made semi-subs are increasingly being used for illicit purposes. However, the WSU project aims to demonstrate how engineer-developed half-submerged vessels can efficiently serve military, commercial and research purposes.
‘A semi-submersible vehicle is relatively inexpensive to build, difficult to detect and can go across oceans,’ said Konstantin Matveev, the WSU engineering professor leading the work. ‘It’s not so susceptible to waves in comparison to surface ships since most of the body is underwater, so there are some economic advantages as well.’
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Since the semi-sub sails mostly at the water line, the materials from which it’s made don’t need to be as strong as those used to make a submarine, which has to withstand the pressure of being underwater for long periods of time. The semi-sub also has the advantage of having a small platform in contact with the atmosphere, making it easier to receive and transmit data.
For this study, Matveev and co-author Pascal Spino, a recent WSU graduate and former president of the WSU RoboSub club, tested the semi-sub’s stability and ability to manoeuvre in the Snake River’s Wawawai Bay in Washington state. It reached a maximum speed of 1.5 metres per second (roughly 5.5 km/h), but they found that when it was moving at high speed, it rose above the water, creating more of a wake and expending more energy. At lower speeds, it’s almost fully immersed and barely makes a ripple.
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The researchers also outfitted the semi-sub with sonar and mapped the bottom of a reservoir to test its ability to collect and transmit data.
While not yet completely autonomous, the WSU semi-sub can be pre-programmed to behave in certain ways, such as running a certain route by itself or responding to particular objects by either pursuing them or running away.
While the semi-sub is relatively small at 45 centimetres long, with a ten-centimetre diameter, according to Matveev, larger semi-subs could be built to carry significant cargo. For instance, they could be used to help refuel ships at sea. They could even be scaled up to rival container ships, and since they experience less drag in the water, they would use less fuel, creating both an environmental and economic advantage.
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For now, the Matveev’s lab is continuing work on optimising the shape of semi-submersible-vehicle prototypes to fit specific purposes. He’s currently collaborating with the US Naval Academy in Annapolis, Maryland, to work on the vehicles’ operational capabilities and compare numerical simulations with results from experiments.
The research has been published in Unmanned Systems.