The Vineyard Haven harbor’s two pump out boats carried between 12,000 and 15,000 gallons of raw sewage from holding tanks on boats to the town’s sewer system during this past boating season, according to harbor master John (Jay) M. Wilbur 3rd.

And as the demand for pump outs increases every year, the town harbor department is beginning to have trouble coping, Mr. Wilbur said.

“Our main boat here in the harbor is operating eight hours a day, seven days a week to try to keep up with the demand,” Mr. Wilbur said. “The average waiting period for someone who wants a pump out has gotten to be two hours. If someone calls at 10 a.m. for a pump out, we probably can’t get to them until noon because there’s so much demand,” he added.

Pump outs have become the single most time and resource-consuming task in the harbor department since the program began about 12 years ago. It currently takes two full-time employees and one part-time employee in Vineyard Haven to run the two boats — one for the harbor and Lagoon and one for Lake Tashmoo. The service is free; boaters call for pump outs on VHF channel nine.

Demand has increased by about 20 per cent every year, Mr. Wilbur said.

“It’s a demand that we’re having difficulty keeping up with,” he said. “It’s become evident that we need more capacity — more than just the two boats.”

But beyond another boat, the harbor master said he would rather see a change in the pump out system itself — and a reduction in the number of pump outs that he views as unnecessary.

With increasing frequency, boats about to embark upon voyages into open ocean call upon the harbor department to pump out their holding tanks, Mr. Wilbur said.

“I’ve noticed people becoming really dependent on it in the last couple years. The people call up and say ‘Hurry up and pump me out because I’m leaving,’ ” the harbor master said. “I don’t want to be construed as feeling like people shouldn’t be pumping out while they’re here in the harbor — I absolutely believe that’s vital — but I don’t believe they should be pumping out before they leave, unless they’re just going to Oak Bluffs.”

State and federal law allows boaters to empty their holding tanks more than three miles from shore. But with growing public concern about water pollution, an increasing number of boaters are refusing to dump anywhere in the ocean — even far out at sea.

Many say that’s good news for the ocean, but closer to home, Mr. Wilbur worries about the impact on Vineyard Haven and its sewage treatment plant from all the extra pump outs.

The treatment plant’s leaching fields lie in the watersheds for Lake Tashmoo, the Lagoon and the harbor. Once it reaches the leaching fields, treated waste is free of bacteria but still contains some nitrogen.

“There’s no science that I know about that indicates [legal ocean dumping] is bad,” Mr. Wilbur said, adding: “My problem with that kind of PR is it influences recreational boat owners to think it’s bad. They won’t do it, so they end up depending on us.”

Mr. Wilbur said it is inefficient and potentially risky to transport waste between boats and the town sewer system. The boats, which are custom-built and expensive, also break down regularly because they are so complicated, he said.

“It doesn’t seem practical anymore — now that there’s a sewer — to remove the stuff from a boat that’s tied up somewhere and take it somewhere else to where there’s a sewer. It should go directly from where they’re tied up to the sewer,” he said. “If the town had that access, there would be a shoreside facility by now.”

Until the town began using pump out boats three years ago, waste from boats was transferred from Tisbury Wharf Company into a giant holding tank under the parking lot. It was then shipped to New Bedford, processed at a treatment plant and pumped back into the sea. Now, the waste goes into a pipe at the Tisbury Wharf Company that leads directly to the town sewer.

Owen Park is not close enough to the treatment plant to have a shoreside facility where boats could pump directly into it. The only way Vineyard Haven could have a shoreside facility is if a private marina or boat yard built one, Mr. Wilbur said. Government grant money is available for that purpose, but the marina or boat yard would have to apply for it.

Melinda Loberg, a member of the Tashmoo and town harbor management committees, said it’s only a matter of time before the Steamship Authority also starts pumping out its ferries on shore — probably on both the mainland and the Island. Currently, the ferries treat sewage on board and then discharge the treated water into the ocean.

But Mrs. Loberg said there are bigger problems facing coastal waters and shellfish than waste pumped from boats.

“I think our local septic systems are contributing in a much more serious way to the shellfish [pollution],” she said.