"The first one they made didn't work," Vessey said. "They were coming at it from the point of view of how it would look. ... It had them perplexed there for a while."
The man who finally stumbled upon the winning design, she said, was a wildlife photographer who had spent significant time watching birds and fish swim.
The tail is actually designed to take on water as Vessey wriggles into it and releases water as she takes it off.
To coax the nearly 10-pound suit on, Vessey sits on the edge of the water in her swimsuit and puts her limbs into the socket. But because it zips up the sides and clips over the shoulders, she can't do it alone.
And it has forced Vessey to learn a new way to swim.
"You've got to do a dolphin kind of movement," she said. "It takes a strong lower body. ... I have to learn to swim a different way. Once you've learned one way, it's difficult to unlearn that."
But since the tail's completion in December, she has taken it for a dip in the ocean about seven times, capturing the imagination of locals at the beach and people all around the world.
A good friend of hers has even written a children's book, titled "The Mermaid Who Lost Her Tail" in Vessey's honor. Vessey herself started to write a story about her tail adventure, but then passed it on to a friend who recast it as a tale about a mermaid who was washed ashore, adopted by a family and lost her tail as she grew up.
As she came to live on land, she needed "dollies' legs" (which is what Vessey sometimes calls her prosthetics) but then sought out help from a crew of "Wonderful Wetas" for a tail to return to sea.
Growing up, Vessey never fantasized about being a mermaid but said she had been surprised by the number of women and girls who have stopped her to exclaim wonderment about her newest prosthetic. She also said she hopes it encourages other people with disabilities to consider creative alternatives as she did.
"I've been really quite touched by people's reactions," she said. "The response has been such that it gives people hope, just thinking a little outside of the square."