For the Vineyard it means expanded ferry service using high speed travel from the port of New Bedford and no new double-ended ferry to replace the beloved Islander.

For Nantucket it means replacing three familiar old ferries with one new multi-purpose high-speed ferry whose design has never before been tested in this country.

For the trusty public boat line that has served both Islands for 41 years with no state or federal subsidy, it means a trip to the state legislature to ask permission to take on staggering new debt to cover millions of dollars in capital expenditures.

These are the primary colors of the complicated and ambitious new service model now under discussion in the port communities served by the Steamship Authority.

The service model was first unveiled three months ago by the boat line board and management. The key components of the model include:

* Limiting short-term automobile traffic to the Islands.

* Increasing passenger traffic using expensive high-speed ferries.

* Opening up a high-speed passenger ferry route between New Bedford and the Vineyard.

* Replacing three ferries on the Nantucket run with one multi-purpose high-speed ferry at a cost of $30 to $40 million.

* Redistributing freight traffic by requiring fuel and petroleum products to be carried by barge.

The service model is still only a set of concepts. A financial analysis of the model has begun but is still incomplete. A preliminary analysis prepared by boat line treasurer Wayne Lamson early this month found that the new service model could be "cost neutral."

But Mr. Lamson was also quick to say that cost neutral is only as good as the assumptions in the service model.

And in fact there are many questions about the assumptions.

At the outset it appears that the projected expenses are optimistically low in connection with the multi-purpose, high-speed ferry proposed for the Nantucket run. Depreciation expenses were calculated using a 25-year life span for the ferry, but the actual life span for these aluminum-hulled ferries is thought to be more on the order of a decade. Depreciation for the Flying Cloud, the new SSA high-speed ferry on the Nantucket run, is calculated using a 10-year life span.

There are other problems.

Specifications for the high-speed ferry appear to be flawed. The service model calls for a multi-purpose ferry that runs at speeds of 28 to 30 knots and makes the trip between Hyannis and Nantucket in 65 minutes. But the calculations don't work. The Nantucket route is 24 miles long, but a high-speed ferry cannot cruise at 28-30 knots for the entire stretch; slower speeds must be used for some four miles of that run, in the Hyannis and Nantucket harbors. In order to make the trip in 65 minutes, the ferry would need to travel at some 38 knots for the 20-mile stretch of open water. The Flying Cloud cruises at about 38 knots. But the Flying Cloud only carries passengers; a larger, heavier boat that carries cars and freight as well as people would need much larger engines to achieve a speed of 38 knots. Larger engines consume more fuel; more fuel means higher costs.

Mr. Lamson pointed out in his financial report that the 65-minute trip is necessary in order to run six trips and stay within the limit of an 18-hour operating day. This parameter determines the number of crews needed on the boat - run over 18 hours and it means going to a triple crew. A triple crew means more cost.

Mr. Lamson fingered these problems in his report: "It appears that the characteristics assumed for the new high-speed ferry [to Nantucket] may not be adequate in terms of speed and capacity," Mr. Lamson wrote.

Vineyard SSA governor J.B. Riggs Parker said this week that the specifications for the new ferry are subject to change.

"Certainly the specs are under review. It's all under review. But what the financial analysis shows is that there is good reason to go ahead and vet the first part of the model. This is really just a first step," he said.

The service model forecasts an eventual savings of some $2 million in annual operating costs on the Nantucket run. But other costs will be picked up along the way, including added operating expenses for the New Bedford run.

The list of questionable assumptions goes on.

In his preliminary report, Mr. Lamson noted bluntly that the service model would require a huge new expansion of debt for the SSA. The current bonding limit for the boat line is $50 million; the new service model would require an increase to $75 million.

Any increase in the bonding limit needs the approval of the state legislature.

Cape and Islands Rep. Eric T. Turkington said this week that an increase in the bond limit is by no means guaranteed.

"The position of the House on the Steamship Authority has always been that it is very pleased that this entity does not require any state subsidy," Mr. Turkington said. He added: "And if there is going to be any bonding increase, someone is going to have to come in with a really good set of numbers to show that this will never be a burden on the taxpayers."

Mr. Turkington said there is a clear political downside to requesting an increase in the bonding limit. "There is always the danger that this will become a Christmas tree for someone's ornaments. Who gets to have a voting seat on the board? What about the licensing power? Every time any issue comes up with the Steamship Authority, we have a whole spectrum of people who come out of the woodwork with their wish lists. And that would certainly be the case when it comes to the bonding limit," he said.

And then there is the question of the Islander.

The current capital program for the boat line calls for replacing the 50-year-old ferry Islander at a cost of some $20 million by the year 2007.

But in the new service model, the replacement for the Islander has been erased from the capital budget. The refurbished Nantucket would replace the Islander instead.

The barging component of the service model has not even been discussed yet, and it is not known how this would fit into the overall plan.

It all adds up to a dizzying profusion of facts and a sort of Rubik's Cube of decisions.

Discussions are ongoing in all the port communities on the service model.

But there is a good deal of confusion about the process and a decidedly mixed message coming from the boat line. On the one hand Mr. Parker has said repeatedly that the model is still only a set of concepts.

"It is on the table but not set in stone. The ideas and financials are now subject to rigorous cross-examination. I have not made up my mind about it," Mr. Parker writes in an opinion piece published in today's Gazette.

But in the mainland port communities, there is a somewhat different message coming from the boat line.

SSA general manager Armand Tiberio told a group of New Bedford residents last week that the SSA is already moving aggressively to replace the Schamonchi with a high-speed ferry.

On Nantucket there is growing opposition to the service model.

"It feels sort of like somebody just lobbed a grenade into the whole situation," said Penny Dey, vice chairman of the Nantucket planning and economic development commission.

"The whole issue has become so complicated - there is total confusion and it almost feels as if it was done on purpose. Quite frankly, nobody understands why we would want to do a radical overhaul on something that is working fine," she added.

Much of the discussion may come to a head late next month, when Nantucket is due to hold a public hearing on the service model. And a key question looms: If Nantucket rejects the model, what will the boat line board do?

Mr. Parker said he will not vote to force any plan on Nantucket.

"I think if the Nantucket community informs itself and makes an informed judgment that they do not want a particular service to the Island, it would be irresponsible of anyone on the authority to vote that. The Islanders are the ones who know what the needs are," he said. He added:

"I do believe any expression of approval or disapproval of a service or service model should only come after a real effort to understand it and examine it and accept the consequences of not having such a service. This is a proposal by management and it is being submitted all the way around - and who knows, maybe neither one of the Islands will want it."