Russian billionaire Andrey Melnichenko is building what is believed to be the largest sailing yacht ever built, at a length of more than 480 feet.
According to yacht workers in Germany familiar with the project, the ship will be around 147 meters, or 482 feet. That would easily surpass the 96-meter "Sea Cloud"— built in the 1930s—and the 289-foot "Maltese Falcon," built by Silicon Valley venture-capitalist Tom Perkins and launched in 2006.
Melnichenko, a Russian billionaire who made his fortune from banking, steel and fertilizer, couldn't be reached for comment.
Read MoreCelebrity skinflints stiffing kids
"Sailing Yacht A" would be his second ground-breaking megayacht. Melnichenko also built the motor-yacht named "A"—a sleek, modernist 394-feet ship that has become one of the most photographed and popular in the world. Along with its widely copied knife-like hull, "A" has an interior filled with advanced technology and security systems, Baccarat crystal and gleaming white finishes.
Yet the yacht, being built by Nobiskrug shipyard in Kiel, Germany, is expected to be even more jaw-dropping. According to workers familiar with the project, the ship will have a soaring, open atrium that will rise to three stories. It will also have a massive swimming pool.
The combined mass of the sails will be larger than a football field and the mast system, which appears to be made up of three masts, will be made of super lightweight, high-strength carbon fiber, these people said. It will have a crew of 66 people.
" '[The new yacht]' will make 'A' look like a dinghy," one yacht worker said.
It's unclear how much the ship will cost. But since "A" cost more than $300 million, it's safe to say the new ship will also be nine figures.
"Sailing Yacht A" is still being fitted out, and it's expected to launch in July 2016, according to one yacht worker.
Melnichenko is expected to keep "A" after the new ship is finished, so he'll be able to use his sailing or motoryacht, depending on his mood.
"He wanted to do something unique and eco-friendly with '[Sailing Yacht A],' " one worker said. "And this is certainly unique."
Update: This story has been updated to reflect the yacht's new name and design features.