Moscow ? The workaday cargo ship the Arctic Sea, which for decades plowed the world’s waterways in obscurity, just had to disappear to be thrust into a swirling drama of rumors and intrigue. The plot thickened Saturday as a Russian maritime expert reported signals from the ship’s tracking device and Finnish authorities said there was a ransom demand.

The signals from the Finnish-owned ship suddenly appeared in the Bay of Biscay off France, Mikhail Voitenko reported on his Web site Sovfrakht.

The French Navy dismissed the claim, maintaining that the ship most likely was somewhere in the vicinity of Cape Verde — an island nation off the coast of Africa some 2,000 miles farther south. Widespread reports on Friday also had placed the Russian-crewed ship near the island nation off West Africa, but officials later said it could not be confirmed.

The signal vanished after about an hour and the device that transmitted it could have been dismantled from the Arctic Sea and placed on another vessel, Voitenko said.

“It’s very improbable that the Arctic Sea is now in the Bay of Biscay,” Voitenko told Associated Press Television News. It is believed that the ship last had radio contact there.

Later Saturday, Finnish authorities reported that the ship’s owners received a ransom demand. They gave no details on the amount demanded, the ship’s location or on the 15 crew members. Nor is there confirmation that anyone has seized the ship.

The ship, which its owners say is carrying an Algeria-bound load of timber, set sail from Finland on July 23. The next day, the crew reported, about a dozen men boarded the ship near the Swedish island of Gotland, tied up the crew, beat them, said they were looking for drugs and then sped off in an inflatable craft.

The motive for the alleged attack is unknown and the report itself has raised doubts. Such an attack would have been unusual in European waters, and Swedish police said they started investigating only after hearing about it several days later from the ship’s owners.

By that time, the ship had already passed through the English Channel, where routine radio communication was the last confirmed contact with the Arctic Sea.

The ship’s fate went nearly unnoticed until Wednesday, a week after it was expected to dock in Algeria, when Russian President Dmitry Medvedev ordered his defense minister to take “all necessary measures” to find the vessel.

Russia has dispatched naval ships for the search and NATO is staying in close contact with Moscow. Hopes rise and fall with reports that don’t pan out or trail off inconclusively.

Some reports suggested this week that the Arctic Sea had come into the Spanish port of San Sebastian, even though that port is suitable only for pleasure boats and small fishing vessels.

Speculation has ranged from suspicions that the ship was carrying secret cargo — possibly narcotics — to theories about a commercial dispute.

Voitenko suggested that the people in control of the ship now “just don’t know how to work it out, how to come out of this story with the least possible losses.”

“The story is unique and fantastic,” he said. “I can’t speculate anymore — I don’t have enough fantasy.”