In a move that would tie Martha's Vineyard even more closely to the mainland, Hy-Line Cruises wants to launch year-round fast ferry service between Hyannis and Oak Bluffs by next May.

The high-speed ferry operation proposed by the Hyannis-based company would become the second such service started within a year between the Vineyard and the mainland.

New England Fast Ferry began fast ferry service between New Bedford and the Island last June, and plans to add a second high-speed boat on the route by next May.

Hy-Line's proposed fast ferry would replace a seasonal conventional ferry on a route that the company has run for more than 30 years.

"The market is changing. We need to upgrade the equipment," said Murray Scudder, vice president of operations for Hy-Line. "We want to be more of a player in the Martha's Vineyard marketplace."

Ferry customers prefer faster travel, and ridership has been falling off on the seasonal Vineyard run, Mr. Scudder added.

The conventional ferry, which runs from May through October, travels the Hyannis-Oak Bluffs route in about an hour and 40 minutes. The fast ferry, with a cruising speed of 30 knots, would make the trip in under an hour.

Fares have yet to be set, but Mr. Scudder said that the service probably would sell a round-trip for about $50. In the current off-season, New England Fast Ferry charges $32.50 to Vineyarders for the round-trip, connecting Islanders to New Bedford in one hour. The in-season rate had been $40.50.

Mr. Scudder also said the fast ferry would give Hy-Line the ability to expand opportunities and services for Vineyard residents, as its Grey Lady fast ferries have done for Nantucket.

In a Dec. 17 letter to the Oak Bluffs selectmen, Mr. Scudder wrote, "We believe that the replacement of a seasonal traditional ferry with a year-round high-speed vessel from Hyannis to Oak Bluffs and the Vineyard will contribute to enhancing the quality of life for Vineyarders by opening up educational, health care, cultural, employment and other opportunities on the Mid-Cape to residents of the Island which do not exist at this time.

Hy-Line plans to use the Grey Lady II, a high-speed catamaran. The ferry ran on the Hyannis-Nantucket route from 1997 to 2003, and is the predecessor of the Grey Lady ferry now on the Nantucket run.

Mr. Scudder said Hy-Line is powering the Grey Lady II with four new engines, as well as renovating the vessel to add more interior seating. In its past incarnation, the ferry could carry 149 passengers, 105 of them inside the ferry.

The overall cost to launch the new route, consisting mostly of the ferry renovations, will reach about $1 million.

Before running the fast ferry on the route, Hy-Line must secure a license from the Steamship Authority, which regulates ferries carrying more than 40 passengers between the Cape and Islands.

While the boat line plans a full review of the proposal over the next two months, SSA general manager Wayne Lamson raised concerns Monday about the fast ferry's potential effect on existing SSA passenger traffic to and from the Vineyard. Another high-speed ferry operation could cut into the SSA's group tour business.

The Steamship Authority operates only a seasonal ferry service between Woods Hole and Oak Bluffs and year-round service between Woods Hole and Vineyard Haven - for both cars and passengers.

Hy-Line, founded and operated by members of the Scudder family, plans to use its existing leased dock space at Dockside Marina in Oak Bluffs and its docks on Ocean street in Hyannis for its fast ferry run.

The Dockside Marina facility may have to be slightly modified, Mr. Scudder said. Ferry company officials met with individual Oak Bluffs selectmen last week to discuss the proposal.

Selectman Kerry Scott said the fast ferry could bring a new crop of visitors to Oak Bluffs and offer residents improved access to medical facilities and social services in the mid-Cape area.

But Ms. Scott also questioned the proposed ferry service's impact on the harbor and its environment and whether local businesses will be hurt by residents using the fast ferry to shop in Hyannis.

Robert Marshall, the Falmouth SSA governor, said the proposed service really is not significant for Falmouth.

"We might see some reduction in autos. People would park in Hyannis and go across from there to the Vineyard," he said, while downplaying the economic impact from Vineyard travelers. "What Falmouth gets mostly is fumes," he added. While the new service could skim off some SSA passenger traffic, Mr. Marshall said the boat line could recoup any potential loss in profit by charging a license fee to Hy-Line. In fact, because the SSA does not now operate a Hyannis-Oak Bluffs service, the service could generate revenue that the Authority would not otherwise collect.

Along the same line, Mr. Marshall said, the fast ferry may entice people in the Mid-Cape to travel to the Vineyard who otherwise wouldn't bother, given the length of the drive to Woods Hole. Should the service prove successful, Mr. Marshall said, the boat line might want to explore running its own service between Hyannis and the Vineyard. "This could open up some interesting conversations," he said.

History may be about to repeat itself for the Scudders, who introduced fast-ferry service between Hyannis and Nantucket in 1995.

Their success led the SSA to try to play catch-up: first by leasing a fast ferry for the route, then by building and operating its own fast ferry, the Flying Cloud, on the route. The Flying Cloud entered service in May 2000.

But the Flying Cloud soon became a headache for the boat line, even though the ferry was one of the SSA's more profitable operations. Susceptible to accidents and plagued by engine failures that consistently interrupted service, the ferry became an object of derision on Nantucket, where Islanders referred to the vessel as the "Black Cloud" or "Dying Cloud."

Hy-Line, meanwhile, earned respect in the market for the reliability of its fast ferry service. The Flying Cloud's performance deteriorated to the point where Hy-Line, which faced SSA restrictions on the number of passengers it could carry, was capturing more than half of the fast ferry customers on the route.

The SSA regrouped several months ago, running the ferry's engines at a lower rate, which improved reliability even as it slightly lengthened the time of the trip. Like the Grey Lady, the Flying Cloud makes the trip in about an hour.

But the SSA also threw in the towel for this winter, deciding to take the Flying Cloud out of service from early January into March. During that time, Hy-Line will provide the only fast ferry service on the Nantucket route.