Buoyed by more than $28 million in newly-available federal funding, the Steamship Authority is preparing to buy a third former offshore supply vessel to convert into a freight ferry.

Voting unanimously Monday afternoon, the SSA board of governors authorized general manager Robert Davis to purchase the Lode Star class vessel for $5,673,500, provided the boat passes an inspection that’s expected to cost about $110,000.

The purchase would bring to three the number of pre-owned, offshore supply vessels the Steamship Authority has bought this fiscal year from Louisiana-based Hornbeck Offshore Services, which operates a fleet supplying oil and gas platforms in the Gulf of Mexico.

In September, the SSA closed on two Lode Star OSVs and asked the public for help in renaming them. Boat line staff sifted through thousands of entries to bring a short list to the board of governors, which named the new boats M/V Aquinnah and M/V Monomoy.

The next boat will be renamed in a similar process, from the same pool of entries, SSA communications director Sean Driscoll said Monday.

“We have a robust list of names,” Mr. Driscoll said.

Each of the triplet ships will need an estimated $8 million in shipyard work to convert them into freight boats. SSA director of marine operations Mark Amundsen said Monday that more than two dozen companies have expressed interest in the bidding package.

“We have 27 interested parties... from Rhode Island to the Gulf,” Mr. Amundsen said.

Bids for the conversion work are due Jan. 9, with a contract to be awarded at the governors’ regular meeting later that month, Mr. Davis said.

To purchase and convert the first two Hornbeck OSVs, boat line governors in August authorized borrowing up to $32 million. Those bond proceeds now will fund the purchase of all three sister ships, while the new grants from the Federal Transportation Agency (FTA) will pay for their conversion to SSA freight boats.

The boat line earned the FTA funding by reporting its passenger numbers to the National Transit Database, a practice it began several years ago.

The SSA’s numbers, added to those of the Cape Cod Regional Transit Authority (CCRTA), have increased by millions the amount of federal money available to the region, CCRTA administrator Thomas Cahir said during Monday’s board meeting in the boat line’s Palmer avenue headquarters.

“It’s a very significant accomplishment for our region,” Mr. Cahir said, noting that the shared funding represents 40 per cent of the total allotted to all 53 transit regions in Massachusetts.

A new memorandum of understanding with the Cape Cod Regional Transit Authority, which is the federal government’s designated recipient for Cape and Islands transportation grants, makes about $28.1 million of the funding available to the SSA, on top of more than $7 million that was allocated earlier on.

This may not be the last time SSA governors authorize buying a Lode Star OSV. The boat line still has the option, through March, to purchase a fourth from Hornbeck.

The first of the two already purchased — whether it will be the Aquinnah or the Monomoy remains unspecified — is not expected to join the active fleet until summer is well underway, due to the still-uncertain schedule for conversion and the need for a 30-day training period before a new vessel can go into service, Mr. Davis said.