LAMOINE – Cruise ship passengers who pay thousands of dollars for a week on the water have been getting a free ride once they make land on Mount Desert Island.

Rather than board commercial tour buses, ship passengers hog the Island Explorer bus seats, ride around the island on all-day free tours and drive up costs for the public bus service, according to operations manager Paul Murphy.

Murphy said Tuesday that most of the ship passengers also decline to buy a park pass, despite efforts by the drivers to collect the $10 fees. By piling into the free buses, the ship passengers make it through the Acadia gates without paying, particularly at popular Sand Beach, Murphy said.

And it gets worse, Murphy said. Many of the beach-goers wait until the final bus run of the day to get picked up – and the one closest to their departure time. The result is that sometimes as many as 200 people are waiting for a 28-seat bus, requiring Murphy to ask some drivers to work late and others to leave their regular routes to deal with the influx.

“We should definitely be talking about charging a fee” for each ship passenger, Murphy told a meeting of the Mount Desert Island League of Towns. He said travel agents promote the Island Explorer buses in cruise literature, even though commercial tour buses are readily available in Bar Harbor, where the ships moor for a day on their way to Canada.

Len Bobinchock, Acadia assistant superintendent, prompted the discussion with Murphy when he said, “I’m a little concerned about the cruise ships. If we’re not careful, we could soon become overwhelmed.”

Sixty-four cruise liners were scheduled to visit Bar Harbor this year, a record number. Some of the ships carry only a few hundred passengers; others can accommodate thousands.

The busiest time of the cruise ship season is late summer and early fall, but ship passengers still clogged up the buses during the peak summer tourism season, when more than 1 million visitors come to MDI and Acadia, Murphy said.

The Island Explorer bus system was created four years ago as a commuter service to get island residents and visitors to their favorite restaurants, shops or park attractions.

The propane-powered buses also provide workers with public transportation during the congested summer season, further reducing pollution and traffic.

Murphy said the bus system wasn’t prepared for ship passengers to use the buses as touring machines, since riders typically take the bus to a specific destination.

“They would ride all the way out and all the way back,” Murphy said.

Next year, the Island Explorer will expand its service through Columbus Day, rather than shutting down just after Labor Day.

The bus service is paid for primarily by Acadia gate fees and grants from the nonprofit group Friends of Acadia. MDI communities also contribute about 10 percent of the operational costs of the bus service.