When it comes to making a splash, technique tops brute force. And new research reveals the secret to record-setting splashes.
New Zealand’s Māori and Pasifika communities developed the Manu jump. It’s a cannonball-style sport. Key to its splashiness: Make a butt-first, V-shaped entry, researchers now report. There must also be a well-timed, underwater follow through.
Researchers shared these findings May 15 in Interface Focus.
Their insights could liven up a backyard pool party or help athletes vying for glory in Manu competitions. But aerospace engineering might also benefit from the new findings. They might make spacecraft splashdowns smoother and safer, says Tadd Truscott in Saudi Arabia. A fluid dynamics researcher, he works at the King Abdullah University of Science and Technology.
The Manu method
Manu jumping is a decades-old summer tradition. So-called bombers hurl themselves off bridges, cliffs or platforms. Their goal is to make the most splash. This joyful, chaotic celebration of impact makes backyard belly flops look like amateur hour.
“It’s a fun thing to really master and work on your technique to get the biggest splash,” says Brad Day. A mining engineer from Hamilton, New Zealand, he created a “How to Manu” tutorial.
Saad Bhamla is a biophysicist at Georgia Tech in Atlanta. He and others in his lab were instantly captivated by Day’s video. They also watched clips of other Manu enthusiasts on TikTok and YouTube.
Previous splash research had tended to focus mostly on minimizing surface disruptions. The point is to reduce damage to an object during water landings. Other studies have aimed to perfect an Olympic dive, where splash-free entries receive better scores. Popping a Manu is “the diametric opposite scenario,” Bhamla says.
Splash-test tech
To crack the code of a great Manu jump, Bhamla’s team first collected movement data from 50 online videos (including Day’s). On average, Manu jumpers enter the water at about a 45-degree angle. Their butts hit first, with legs and torsos slanted outward in a V-shape.
“To be able to shoot the water that high is a real skill,” says Scott Rice. “It really comes down to how good someone’s technique is.” Rice created Z Manu World Champs. It’s a competition in New Zealand, first held last year.
The Georgia Tech team then used 3-D–printed projectiles, robotic divers and high-speed cameras while running controlled tests. These confirmed that a precisely angled entry was very important for maximizing splash. It formed a deep pocket of air in the plunging jumper’s wake.
“But what is more important is what you do underwater,” says Pankaj Rohilla. He’s a biomedical engineer on the Georgia Tech team.
Good angles, perfect timing
Bum-first entry is followed by a rapid backward roll and leg extension.
This stretches out the body, and with it that pocket of trapped air from the V-bomb, the new research showed. The gravitational pull of the water overcomes the inertia of the plunging jumper. At that point, the air pocket — a cavity — collapses and pinches off. Then, a towering jet of spray shoots skyward.
But when to execute this underwater unfurling?
The ideal moment depends on both the height of the jump and the size of the jumper, the splashbots revealed. Both affect how deep an air pocket forms.
Stretching out too early makes your body release the air pocket before it fully develops. Stretch out too late and your body expands after the pocket has already started collapsing. That will weaken a splash.
The biggest upward plumes occurred when a robot opened up about halfway through its underwater descent. That sweet spot was fleeting but powerful.
Just milliseconds can separate a good Manu jumper from a record-breaking one, says Patria Hume. She’s a sports biomechanics researcher at Auckland University of Technology. That’s in New Zealand. Hume is part of a team behind the “ManuTech” platform. It is a mix of high-speed video-capture and real-time digitization software.
ManuTech was introduced at Manu competitions, last year, to judge splash sizes. The biggest blasts soared over 10 meters (33 feet) high from jumps just 5 meters (16 feet) above the water.
“These findings could lead to new training tools or techniques to help competitors get that edge,” Hume says. But waterworks are just one element of an overall Manu score. Competitors also earn marks for splash volume. This is measured with hydrophones. (These devices detect soundwaves underwater.)
Splashers also get points for technique and pizzazz. These scores celebrate the expressive, freeform spirit that defines the event.
“While science can help athletes improve their splash, it shouldn’t take away from the freestyle roots of the sport,” Hume says. “Creativity, flair and fun in the air are what make it so unique.”