Four dozen marine engineers and oilers for the Staten Island Ferry and city fireboats saw their ships come in last year — hauling in enough overtime to double their pay, city records show.

The city Department of Transportation employed 37 ferry workers who netted more than $2.5 million in OT, according to an Empire Center analysis.

The six-figure fleet was anchored by chief marine engineer Clifford Aversano, who clocked 1,400 hours of OT in fiscal year 2015 — or an average of 27 extra hours per week. He pulled down $92,051 in overtime cash to boost his total yearly pay to $164,759, the payroll records show.

The ferry workers have a four-day workweek built into their contracts, but the city usually needs them to work more than that to inspect power plants, test engines and emergency systems and conduct safety checks before passengers board, officials said.

DOT officials also cited the ferry’s additional weekend passenger service that began in May 2014 and last winter’s “extreme weather” causing the need for ­additional hands on board.

“Overtime is monitored very closely,” said DOT spokeswoman Bonny Tsang. “We are also working . . . to distribute the work so that no individual will need to work as much overtime as ­occurred this past year.”

The ferry system has long been dogged by charges of nepotism and cronyism.

Nine FDNY marine engineers and oilers seized a total $971,425 in OT booty, led by Frederick J. Domini’s $153,787 in overtime for 2,035 extra hours — or 39 hours of OT per week.

His $262,926 in total pay made him the second-highest paid city employee — even ahead of Fire Commissioner Daniel Nigro ($208,786) and Mayor de Blasio ($224,384). The nine fireboat staffers are considered uniformed firefighters. The FDNY blamed the OT on 10 open positions and said it was working to fill them.

A total of 167,851 city workers gobbled up $1.7 billion in extra pay, according to payroll records analyzed by the Empire Center.