The tourist boat "Robinson" hit rocks near Tsarevo and sank close to shore. It happened around 2am, and one early theory points to a strong squall.
The boat's owner and captain, Georgi Feshev, known as Gundi, broke the news on Facebook.
The wooden boat used to sail from the port of Tsarevo past the bays toward Ahtopol. Over the years, thousands of holidaymakers had traveled on it.
"Today all that's left of it are broken planks on the shore," the captain wrote. He said he struggled to find words, adding that he had put work, time, money and effort into the boat, and that for his family it had been part of their summers in Tsarevo and many memories.
"We're not looking to blame anyone. We're not looking for sympathy. We're just hurting. But we're alive, well and together — and that's what matters most," Feshev added. He thanked everyone who had been part of the boat's story and said his family would move on.
The boat took tourists on one-hour trips, longer excursions and full-day sea picnics. Families with children and organized groups came aboard, and the trips were part of Tsarevo's summer program.
In tour agency listings, Feshev is the captain at the helm who tells visitors about Tsarevo, the port, the Nestinarka and the coastline. Students on school trips to the town named the boat ride among the best parts of their stay.