The cause of M/V Barnstable’s mangled propeller blades and gouged hull remains a mystery, after Steamship Authority engineers said this week the damage could have occurred without being noticed by the ferry’s crew.

A routine dive survey earlier this fall revealed chipped, bent blades on both the starboard and port side propellers, and deep scraping marks were discovered running from starboard to port across the hull.

The evidence indicates contact with a hard surface like rock, Steamship Authority chief operating officer Mark Amundsen said earlier this month, but the mishap — or mishaps — went unreported by captain or crew.

Tuesday morning, SSA director of engineering and maintenance Zachary Lawrence told the boat line board of governors that the contact could well have gone unnoticed during routine ferry maneuvers.

Propeller damage has been fixed.

Courtesy SSA

Propeller damage has been fixed.

Courtesy SSA

“It is extremely possible that this occurred and nobody was aware, especially if it happened when they were operating their bow and stern thrusters,” Mr. Lawrence said, referring to the hydraulic motors used to ease ferries into their slips.

“When they’re running the stern thruster, that — in and of itself — imparts a lot of vibration, and it may be very difficult to discern the vibration from the operation of the stern thruster to striking something,” he said.

Board chair James Malkin, who represents Dukes County, said he had heard differing opinions from informed constituents.

“I’ve been approached by two licensed heavy boat captains. One said it’s very reasonable to believe that nobody would have noticed this. The other said it’s not reasonable to believe that nobody noticed it,” Mr. Malkin said.

Robert Jones of Barnstable concurred with the first assessment, noting that the Barnstable is what he called a “North Sea model” boat with its wheelhouse several decks above the freight deck and even farther from the engines.

“You may not notice the difference of vibration [from] that point,” Mr. Jones said.

The propeller blades were not damaged enough to affect the Barnstable’s performance, Mr. Lawrence said, though the ferry was taken out of service for repairs.

“The captain reports no less vibration with the new blades installed from the transit back from Thames Shipyard, where the repairs were made. This was the same captain who took the vessel to the shipyard,” he said. 

A review of fuel logs going back to May revealed no discernable difference in the Barnstable’s fuel use, Mr. Lawrence told the board.

Port captain Paul Hennessy said he’s looked for clues as well.

“We did review the available data we have,” Mr. Hennessy said.

“Transit [tracking] only goes back to 90 days … the video goes back 60 days, and there’s no abnormal docking. It is a mystery,” he said.

The next step, Mr. Lawrence said, is to look for answers beneath the surface of Hyannis harbor once the waters are calm enough for an accurate survey.

“Right now, we’re awaiting a weather window,” he said.

The Barnstable is the first of three identical offshore service vessels, originally built for the oil and gas industry, that the Steamship Authority has purchased and converted to freight ferries that can also carry passengers.

Commissioned last February and assigned to the Hyannis-Nantucket route, it was joined in May by M/V Aquinnah on the Woods Hole-Martha’s Vineyard run.

The third sister ship, M/V Monomoy, has completed its conversion at Alabama Shipyard, where it has been waiting for U.S. Coast Guard inspections that were delayed by the recent government shutdown.

Mr. Amundsen said Tuesday that the guard’s marine safety center, which administers the inspections, is back in operation and he expects the Monomoy to be cleared for departure from Mobile, Ala. before long.

“We’re right now doing onboard testing … and right after Thanksgiving, we’ll be looking at sending a [crew] down,” he said.

To date, the Steamship Authority has spent nearly $85 million dollars on the triplet ships, out of a total now projected at $86.1 million.