As waistlines have expanded, the Island’s ferry lines have had to keep up, and new rules about more massive passengers that went into effect in December have some Island lines – though not the Steamship Authority – cutting back capacity.

It’s not news that the average American has gotten heavier since 1960, 25 pounds according to the Coast Guard, which has revised its assumed average weight per passenger from 160 to 185. The new number – derived from information from the Centers for Disease Control – affects how many passengers ferries are able to carry.

For the Island Queen, which services Oak Bluffs from Falmouth, it will mean a capacity of 80 fewer passengers per trip this summer, down from a maximum load of 600 passengers and crew to 520. But Island Queen general manager Todd Bidwell says that he isn’t concerned.

“We’ve known this has been in the works for about three years so we’ve been getting all of our systems in place,” he said. “We don’t think it will necessarily mean we’ll do less business. On the busiest days it will simply mean that some passengers will have to wait for the next trip.”

Mr. Bidwell was diplomatic about whether he has noticed his customers pack on the pounds over the years.

“We see really a mix of passengers of all sizes,” he said. “For every person that might be overweight we’ve got other people with surfboards and bikes who are coming to the Island to enjoy the outdoors and be active. We really see people and families of all shapes and sizes.”

Ferry company operators are faced largely either with reducing their capacity or proving – through an elaborate testing system – that their vessels are stable enough to handle the added weight.

Hy-line Cruises Vice-President of Operations R. Murray Scudder says that the new rules will not affect the line’s high-speed ferries that shuttle between Hyannis and Oak Bluffs. “There’s enough margin in their stability that the new calculations did not affect our current certificates,” he said.

For the line’s larger ferries, however, such as the Brant Point which also serves the Vineyard, the company was forced to reduce capacity slightly, though Mr. Scudder says it will not affect the company’s bottom line.

“With the larger ferries, rather than go through a new stability test to see whether we had to change the capacities, we just reduced it since we don’t approach those capacities now anyway on the vessels. It won’t have a bearing on our usable capacity because we don’t take that many folks on the big ferries anymore.”

Steamship Authority general manager Wayne Lamson said his line was similarly unaffected by the changes.

“It doesn’t have any effect on us,” he said. “We had to submit documentation to the Coast Guard with new stability calculations using the higher average passenger weight. As it turned out it didn’t reduce our passenger limits at all.”

The rules have been in the works for years and as a result the Steamship Authority’s two newest vessels, the Island Home and the Iyanough, were built to the specifications of a heftier clientele.

In Edgartown Chappy ferry owner Peter Wells says that his boats were tested years ago with the new weight limits in mind and has had no change in capacity. In Falmouth, Patriot Party Boat owner James Tietje described the so-called stability experiments his boats the Patriot Too and the Minuteman had to endure to prove that they could handle the new limits.

“A marine engineer comes up with a stability model for the boat in his computer. Then he puts pendulums on the boat and puts a certified weight on the vessel, which could be sand bags, lead weights or buckets of water. Then they’ll shift the weight towards one side of the boat and they’ll observe the amount of lift on the pendulum and go back to the computer and check it against their model to see if it lines up. It takes the better part of a day, then after that the engineer is crunching numbers for days.”

Mr. Tietje says that the higher weight limit is a sign of the times.

“The numbers were upped to reflect a more realistic weight of our well-nourished population,” he said.