The Coast Guard is working to determine why a 477-foot-long tanker ship hit three moored sailboats Wednesday near the mouth of the Piscataqua River, on the Maine-New Hampshire border.

A Coast Guard spokesman said the unoccupied sailboats were damaged when they were hit by the tanker around 3:52 p.m. One sailboat’s mast was broken, but all three remained afloat.

Coast Guard officials identified the tanker as the Chem Venus. Lt. David Bourbeau said the Coast Guard believes the tanker’s crew ran aground on a ledge near Goat Island in Portsmouth Harbor, lost control of the steering system and hit the sailboats.

Bourbeau said the collision apparently caused no injuries or river pollution.

The tanker was carrying cooking oil. Bourbeau said the amount of cooking oil has not been determined yet.

The Coast Guard launched two 47-foot lifeboats from its station in Portsmouth Harbor to investigate the crash and contact the affected boat owners. It said the sailboats were moored at the Kittery Point Yacht Club in New Castle, New Hampshire, on the south shore of the river. The clubhouse faces Seavey Island, home of the Portsmouth Naval Shipyard in Kittery, Maine.

“Ships from all over the world pass before (the yacht club), vying with local lobster and fishing boats during the week and hundreds of pleasure boats on holidays and weekends,” the yacht club says on its website.

According to the MarineTraffic.com website, the Chem Venus’ gross tonnage is 11,625 tons and the ship sails under a Panamanian flag. It was going down the river toward Portsmouth Harbor when the collisions occurred.

Glenn Kisch, who lives on Goat Island and saw the collisions, said the tanker was being escorted by two tugboats as it rounded Henderson Point. There is a sharp bend in the Piscataqua River between Goat Island and Henderson Point, according to aerial maps.

“It was not so much frightening as it was shocking to see the tanker miss its turn at Henderson Point,” Kisch said.