Racing under water

Read the Dutch article here

A ‘giant manta ray’ glides majestically through the water, its wings powered by a diver in a wet suit, pedalling fit to bust. Meanwhile, a ‘tuna’ with a large mechanical tail makes frantic attempts to get its head off the bottom. Left and right, cyclists flash by in cigar-shaped cocoons, leaving a long trail of air bubbles.

Ordinarily, the US Navy patrol uses its kilometre-long indoor basin in Maryland – the David Taylor Model Basin – to test patrol ships and other military vessels. During the two-yearly International Submarine Race (24-28 June), however, the long pool becomes the playing field for some 20 teams of secondary school and university students, most from North America. With their hand-made, human-powered submarines, they race in 100-metre sprints. The race has been held here since 1995. Before then, participants cycled under water off the coast of Florida. This was far more spectacular, but also more difficult to organise. 

The world speed record is 7.2 knots: 13.3 kilometres per hour “We should be able to break that record”, says Gijs Bloemen by phone from the USA, halfway through the race. “Our submarine, the Wasub III, is designed to travel at 7.3 knots.”

Bright red cigar

This is the first time since the Wasub II fiasco that a group of TU Delft students have dared to cycle under water. In 2006, the Wasub II smashed to pieces when it crashed into the wall during an underwater race near Los Angeles. Gijs Bloemen is leader of this new Wasub III team from TU Delft.

The team consists primarily of third-year students of mechanical engineering and shipbuilding. They have been working on their submarine for an entire year in the Dream Hall on campus, where the solar car Nuna and a host of other fast or efficient cars are being built as well. The submarine ultimately took the form of a bright red, elliptical cigar that keeps the flow along the hull laminar for as long as possible.

The underwater bicycle from TU Delft looks fast, and the team is therefore taking part in the class for speed demons: the propeller category. Drivers in this class cannot afford to be claustrophobic. Participants in this class do not imitate stingrays or other weird fish; they have cocoons in which their drivers can just lie flat on their bellies, facing forward. They pedal to turn a propeller.

Or in the case of the TU Delft students, two propellers. Wasub III has two contra-rotating propellers, one behind the other. One rotates to the left and the other to the right. This makes the boat much more stable. In addition to forward propulsion, each propeller also exerts a force that allows the submarine to turn on its own axis. The contra-rotating propellers exert opposing forces that cancel each other out.

Self-confidence

This drive system is one of the reasons why team leader Bloemen thinks that his team has a good chance of victory. “I must admit”, he says, “that some of the other teams also have contra-rotating propellers. “But they are not nearly as good as ours. We were assisted in the design by MARIN researcher Jan Hamilton, one of the originators of the Hamilton-Mackenzie power prediction for ships and a big name in marine technology.”

The fact that the Wasub I performed well back in 2005 reinforces Bloemen’s self-confidence. In that year, the Wasub I finished in first place in the category of one-person propeller submarines. With a speed of 12 kph, the submarine was even then approaching the current world record.

Halfway through the race, however, the Wasub III had reached a speed of only 5.15 knots (9.5 kph). So it was nowhere near fast enough. And their major rival, the Canadian team Omer, of theÉcole de technologie supérieurede Montréal, was already running sprints at a rate of nearly seven knots.

Practice makes perfect. Omer, which holds the world speed record, has been participating for more than 20 years. Many other teams have also been racing for 15 to 20 years. The internet offers countless videos of participants testing their boats in open water. For example, for months, the team from Florida Atlantic University has been merrily completing laps in the Atlantic with their latest boat. A video on YouTube shows students from Washington University taking all kinds of measurements on their underwater bike in a large lake.

Blocked pedals

These tests stand in stark contrast to those of the TU Delft students. In May, the Wasub team conducted a week of tests in Marin’s towing tank in Wageningen. Because that tank is narrow, the cyclist had little leeway for adjusting his course. Team members used ropes to keep the submarine under control.

In this case, the cyclist was Jasper de Wilde, one of the designers of the submarine, and not the semi-professional cyclists Peter van Agtmaal and David van Eerd, who would be racing in the US. The reason for this team exchange is that one of the cyclists had a cold and the other had not yet earned his diving certificate.

The difficult start in the race might be because the TU Delft students had been able to practice so little. Right after David Van Eerd clocked in at 5.15 knots, he slammed against the side. The pedals blocked, making it impossible for him to keep the boot on course. The collision was not as drastic as the one in 2006, but there was damage. A fin broke off. The damage has since been repaired.

The Dutch contenders also struggled with finding the proper buoyancy. They were not the only ones. The miniature submarines, which fill up with water, are trimmed with floats and weights. This is very precise work, as evidenced by the many boats that do not reach the finish line and end up bobbing on the surface.

“We encountered two problems”, Bloemens reports. “First, in the towing tank at Marin, we had practised at a depth of two metres, and now we’re having to sail at a depth of seven metres. The pressure is greater at that depth. The Wasub was not equipped for this. Another problem was that the Navy rejected our diving tanks because they had been certified in Europe, and not in the United States. We therefore had to buy other diving tanks with a different mass.”

Automatic pilot

Aside from the fact that the students were forced to perform this kind of fine tuning in the US, several technical aspects ensured that the TU Delft team was facing formidable opponents.

For example, Omer uses a different trick from the one used by the Wasub. It has a kind of gear system built into it. This system can adjust the angle of the propeller blades such that the propulsion increases during the race and with it, the pedalling resistance. This allows the cyclist to accelerate better. This is not a luxury when you have only 100 metres to prove what you can do.

Other teams had equipped their boats with accelerometers and automatic pilots. This keeps the cyclists from having to make continuous adjustments, thus improving their concentration on the power effort. “We also tried to make an automatic pilot”, Bloemen tells us, “but we didn’t have enough time for that.”

Despite all of these drawbacks, Bloemen thinks that his team can win. “Our cyclist has yet to go full throttle. We’ll be seeing that in the days to come. He’s starting to gain confidence and a good sense of steering.”

Once they find the proper balance, the TU Delft crew will have a great advantage over the other teams, as Bloemen explains. “Our exhaust is regulated better. Most of the submarines have holes on the top to release the air that the cyclist exhales. The exact place at which the air escapes keeps changing. That makes the boats unstable. In contrast, we lead the air through a hose to the back.”

This solution is not high-tech; quite the contrary. The Dutch navy had given the students an ancient breathing apparatus with only one round outlet for exhaled air. They were able to attach the hose leading to the back of the boat to this outlet. “A breathing apparatus usually has two oval outputs on the sides. That makes it more difficult to attach a hose – and you don’t want to mess with a breathing apparatus. It has to be safe. The Navy still had this old apparatus lying around in a closet as a backup.”

An inventive propeller system and an apparatus from the Cousteau era – hopefully, these will help the Wasub to move up in the standings.