Monofins were swimfins which were designed to move both feet at once. In this way, a swimming could move with both legs in tandem while efficiency and speed.
The concept was first proposed by Leonardo da Vinci in the early 1500s. The first working was built in the early 1700s by Benjamin Franklin. However, it was French naval officer Lieutenant Commander Louis de Corlieu who succeeded in inventing swimfins in 1914. After retiring from the Navy in 1924, Corlieu focused on his invention which he called propulsuers. He secured a patent in 1933. Corlieu started mass production in 1939 at the beginning of World War II. It was his American business partner, Owen Churchill, who gave them the name swimfins. They saw use in World War II during the D-Day invasion. After World War II, swimfins became a common swimming tool. Humans, as it turns out, are wasteful creatures in the water. The best swimmers were only 5% efficient. Conventional swimfins only helped a little. Monofins were introduced in 1972, but they did not become common until the early 21st century.
There were two kinds of monofins that became popular: the Lunocet and the PowerSwim.
Tech Level: 10
In the early 21st century, American inventor Ted Ciamillo invented the Lunocet monofin after studying the morphology of the dolphin. The hydrodynamic shape was similar to the wing of an airplane. Efficiency was increased because the Lunocet created a forward-moving force which propelled a person more efficiently. People could go as fast as 13 kilometers per hour, fast enough to breach like a dolphin. Less oxygen and effort was needed. The Lunocet led to a new era of hydrotouring. The Lunocet was not the only monofin invented.
Tech Level: 10
The PowerSwim monofin was invented for applications in which efficiency was more important than speed. Although slightly slower than a Lunocet, the Powerswim had 80% efficiency. The Powerswim took the strain off the calves and ankles and redistributed it to the glutes and the quadriceps. The Powerswim undulated up and down creating rolling currents for propulsion. There was just one problem. It took a few hours to get used to because the swimmer had to semi-crouch.
Monofins would be used over the course of the 21st century and beyond. However, for some people, especially women and some men, monofins became obsolete to those who chose to modify their DNA to become mermaids, anthropomorphic whales, and anthropomorphic fish.