Since 1964, the tall ship Shenandoah has brought picturesque maritime charm to Vineyard Haven, moored in the same place in the harbor. But maybe not for much longer.

The Army Corps of Engineers has written to the owners of the 150-foot wooden sloop, the Douglas family, threatening to suspend the permit for the ship to moor there unless they can come up with some solution that resolves persistent complaints from the Steamship Authority that the Shenandoah is a hazard to ferry operations.

The letter, written last month, may finally bring to a head a long-running dispute between the SSA and the Douglases. It will be followed up this week with a meeting of all the parties, the SSA, the Army Corps and the Shenandoah’s owners, aimed at finding compromise.

The problem is, no compromise appears possible to either side. The SSA wants the old ship moved at least a boat length — about 150 feet. Her owners, and the town of Tisbury, believe this would play havoc with other moorings in the harbor.

The origins of the dispute go back to 1998, said Morgan Douglas, captain of the Shenandoah, yesterday. That was when the corps of engineers formally permitted the vessel’s current mooring — where it had already been for 34 years.

But the approval came with a rider: that if the SSA found the positioning affected their operations, they could seek to have the ship moved.

SSA general manager Wayne Lamson said this week that condition was sought by the SSA because the boat line was unhappy even then with the Shenandoah’s position. More specifically, they were concerned about its position on those days — maybe three to five in 100 — when strong southeasterly winds cause her to swing on her mooring into the path of ferries.

“But we were willing to see how it worked,” Mr. Lamson said.

“It didn’t work. I started getting letters from the captains of ferries saying they had to cancel this trip or that trip because they were afraid they wouldn’t be able to make the docking with the Shenandoah in the way.”

In some conditions, the wooden boat was only a couple of boat lengths from the end of the slip.

Mr. Lamson said he first raised the problem with the owners at the beginning of 2006.

“For two years and more of trying to find an amicable solution to the issue,

we have not got anywhere.

“There was a meeting with the Tisbury selectmen in 2006. Then another meeting with the Coast Guard and the Army Corps of Engineers. What came out of that meeting was an understanding the two parties were going to get together and come up with a compromise.

“Right after that I got a letter from their attorney saying they were willing to put reflectors on the vessel and hoping that would satisfy our concerns,” Mr. Lamson said.

“That’s as far as they were willing to go.”

Mr. Douglas says otherwise. At a meeting of the Tisbury selectmen this week, he said his side had explored other possibilities, including shortening the mooring line, but they would not achieve the desired result.

The SSA’s demand, he said, could not be met without “so drastically shortening the schooner’s chain, it would be a sitting duck” in bad weather, or removing other moorings to accommodate a repositioned Shenandoah, or taking her out of the harbor altogether.

His analysis was supported by harbor master Jay Wilbur, who suggested the problems were more due to operational shortcomings of the SSA vessels, particularly the new Island Home, than to the Shenandoah’s location.

Indeed the letter from the Army Corps to the Douglases mentions only the Island Home, although Mr. Lamson said other boats also experienced difficulty.

At Tuesday’s meeting, the selectmen noted a degree of intransigence on the part of both parties in the past and urged Mr. Douglas to find compromise. A major reshuffling of moorings — and possible loss of some — would be a cost to the town too.

But as of yesterday, Mr. Lamson still was insisting the Shenandoah be moved 150 feet, and Mr. Douglas still insisted it could not be done.

Said Mr. Douglas: “It’s important for people to understand what the potential outcomes are here. The Steamship Authority has started a process whereby a Vineyard landmark can be removed from a spot where it’s been for over 45 years.

“And they’re using as an issue a claim that there are safety concerns over the navigation here in Vineyard Haven harbor.

“That’s not something that any mariner should take lightly. But the Steamship Authority has continued to operate in a way which they claim to be unsafe, throughout this entire process.

“They haven’t changed any of the things they have direct control over, while claiming public safety issues,” Mr. Douglas said. “And Shenandoah’s been in the same place in Vineyard Haven harbor since 1964.”

Mr. Lamson was hardly any more conciliatory.

“It’s now in the hands of the Army Corps of Engineers and I understand they’re waiting for some guidance, some recommendation from the Coast Guard on what they think is a safe thing. But we maintain it must be a minimum of one boat length,” he said, adding:

“I don’t expect that to be a long drawn out thing.”