A Human-Powered Fish-like Racing Submarine

In July 2016 submariners from the University of Auckland Biomimetics Lab, using the human-powered submarine ‘Team Taniwha’, beat 10 other teams from around the world to win the third European International Submarine Races (eISR).

The races were held in the giant QinetiQ Ocean Basin at Gosport, England; a testing tank for small submersibles and ship models that is the size of a football field underwater. Submarines were driven by a pilot, breathing on scuba and pedalling or pumping their legs inside a non-pressurised wet hull.

For Team Taniwha this was more than a sporting competition. Unlike the majority of its propeller-driven rivals Taniwha II is powered by fins; a modified double Hobie MirageDrive with one set on top and another set underneath, mimicking the dorsal and anal fins of the leatherjacket (see Figure 1). The team approached the competition challenged with proving fin drives can be reliable and fast compared with propeller-driven boats. Taniwha II was the second fastest sub there, beaten only by the world record holders for propeller-drive submarines. But it was our reliability and manoeuvrability that made the difference and set us apart from the others!

This was our second trip to Gosport. In 2014 we competed in the second eISR, but at this time our submarine was very unstable. Our pilot could go fast but would inevitably crash into the bottom or breach the surface like a small whale. We also suffered from breakages in the string cables that linked pilot control levers to rudder and dive planes. As a result we never completed the course.

An analysis of the unstable 2014 design showed that our dive planes were placed too far forward along the hull. If, for instance, the sub started to nose up a little, the forward-mounted dive planes would introduce a lifting force that would make matters worse. Shark pectoral fins are at the front, but they can bend their bodies up and down and side to side, have quick reflexes and a superb sense of balance to control their swimming; the result of 400 million years of evolutionary development. Without sensory systems evolved for underwater navigation, our pilot, lying prone in a rigid sub, could not counteract a nose-up or down orientation in time to stop the sub from continuing to rotate beyond the point of no return.

Our solution was to move the dive planes toward the aft end of the submarine. This made the sub stable (see Figure 2). If, for instance, the sub turned upward, the rear-mounted fins would produce a counter force bringing the submarine back to the horizontal. The trade-off being manoeuvrability in the vertical plane.
We also had problems with control-line breakage. Rudder and dive planes were joined to the pilot’s controls using string. On our most successful 2014 run our sub made it three-quarters of the way around the course only to crash into a ladder at the side. Our pilot got to this point while valiantly holding on to a broken rudder cable.
Our solution was to replace the string system with hydraulic lines; produced by filling pneumatic (air) cylinders and their tubing with water. The result was a reliable control system.

We demonstrated the effectiveness of both changes at a race in USA in June 2015: the 13th International Submarine Races held at the Naval Surface Warfare Centre in Carderock, Maryland, near Washington DC. The race, held in a kilometre-long ship model testing tank, was more of a drag strip – each sub ran one at a time along a 100m straight line course past a timing gate. Taniwha was fast, completing 10 of 11 runs with a top speed of 3.65 knots, slightly less than two metres a second, like a brisk walk.
At this point, Taniwha was reliable and fast, but before returning to Gosport for the 2016 European races, we needed improved manoeuvrability. In 2015 we were using a rudder for this and it was effective at steering in the tank at the 2015 races. But we wanted something radically different and new – a bending body. This was our second lesson from the leatherjacket. Like all fish it uses its body not only for propelling itself forward but also for steering. Steering by body bending was not only novel; it was to prove to be extremely effective.

But we were faced with a problem: how can you steer a sub left and right in a bending body with only one available hand? One of our students found the answer. A multi-segmented body could be made to bend around in a nice smooth curve, using one lever control through an articulated series of panels linked with cables and pulleys (see Figure 3). A prototype was built, proving that the idea could work. The back quarter of Taniwha’s hull was cut off and we set to work building the fish-body bending device. A single hydraulic cylinder, controlled by a lever on the driver’s left side, would bend the body. We covered the bendy-body segment with a neoprene skin that could be unzipped and removed for inspection of the drive. Tests in the pool showed that our rudderless fish bendy submarine worked. There were other things added to the list of innovations on the new Taniwha, including hydraulic brakes, like the brakes on a glider, that popped out from the sides of the hull (see Figure 6). We were ready for the eISR to demonstrate our aquatic maturity!

On the Friday before the race our divers were given a check-out test. We also demonstrated that our pilot could safely exit the sub in an emergency and that our emergency safety buoy (to alert the UK Army divers that there was an emergency) worked. The new Taniwha completed its very first practice run around the QinetiQ course with a GoPro mounted in front; providing the world with a pilot’s-eye view of the racecourse.

As the week progressed we got faster and faster. Our top speed on Monday was 2.7 knots. On Tuesday, with some small adjustments to the stiffness in our fins we made 3.8 knots, beating our top speed (3.65 knots) at Washington DC. On Wednesday we were faster: 3.9 knots! We found speed by taping over every hole in the body to improve hydrodynamic efficiency. With our second run on Thursday morning we broke the 4 knot barrier (4.3 knots). The world record was in our sights. On the third run we hit 4.7 knots! The race officials told us that we were the world record holders for non-propeller single-pilot submarines. That afternoon we decided to rest on our laurels, relax and go shopping. We all needed some gear for the black-tie reception on Friday night at the Royal Navy base. We should have stayed in the water that afternoon – on Thursday evening the race officials informed us there was a mistake and that the actual record was 4.9 knots. We were fast but still not fast enough.

Friday, our last day, was to be an invitation-only agility event: twice around the course. We qualified. However, twice around the course required double the air. We substituted a 10 litre bottle for our 5 litre bottle. The larger 10 litre bottle interfered with leg movement and this hampered speed. Our pilot Chris nobly tried to beat the record and complete the course. The world record was not broken but we performed well in the agility event. We were the overall winners for the week and thankfully we were appropriately dressed for the occasion!

We have demonstrated that finned propulsion is fast and that a flexible body can be highly manoeuvrable. The world record is still in our sights. We’ll go for this in 2018 when we return to Gosport for the 2018 forth European International Submarine Races!
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www.biomimeticslab.com

AcknowledgementsTeam Taniwha wishes to thank our generous sponsors for their support: Air New Zealand; the University of Auckland (Auckland Bioengineering Institute, Centre for Advanced Composites Research and Department of Engineering Science); Dive New Zealand magazine; Global Dive, Westhaven; Jackson Electrical Ltd; Bodyworks Panelbeating and Painting Ltd; Mainfreight Ltd; Pope Packaging; Seaquel Wetsuits; and Mr Paul Williams.