COPENHAGEN, Denmark (AP) — An amateur-built submarine financed through crowdfunding sunk in Denmark’s waters south of Copenhagen on Friday, but the owner and builder who was alone onboard is safe, the navy said Friday.

The navy initially said the UC3 Nautilus was “found sailing” south of Copenhagen. But navy spokesman Anders Damgaard later said the 40-ton, nearly 18-meter-long (60-foot-long) submarine had sunk.

Peter Madsen, who built the vessel that was launched in 2008, had “been taken over to one of our ships,” Damgaard said. He declined to give further details.

Footage aired on Denmark’s TV2 channel showed the 46-year-old Madsen getting off what seemed to be a private boat and making a thumbs-up sign as he walked away.

“I am fine but sad because Nautilus went down,” he told Denmark’s TV2 channel. Madsen said “a minor problem with a ballast tank … turned into a major issue” that ultimately caused the vessel — considered the largest privately-built of its kind in the world — to sink.

“It took about 30 seconds for Nautilus to sink and I couldn’t close any hatches or anything. But I guess that was pretty good because I otherwise still would have been down there.”

The ballast tank is a compartment that holds water, which is used as ballast to provide stability for a vessel.

“He told us that the journalist who also had been on board had been dropped off Thursday evening,” Damgaard told The Associated Press. Swedish media said the reporter was Swedish. “They were the only two on board yesterday.”

After the submarine was reported missing early Friday, the navy had launched a search from Copenhagen to the Baltic Sea island of Bornholm with two helicopters and three ships, and encouraged members of the public with boats and sonar to search, too

“He told us he had technical problems” to explain why the submarine failed to respond to radio contact, Damgaard said.