AUGUSTA — Bath Iron Works shipbuilders who are represented by the international Machinists union have overwhelmingly ratified a new four-year contract that includes pension enhancements and wage increases.

The agreement approved Sunday by a 1,610-342 vote is the best in the industry, according to Machinists spokesman John Carr.

“We truly know it’s the industry leader in shipbuilding,” Carr said. The workers will receive a $3,000 bonus, in addition to pay increases. Averaged out over the workforce, the pay increase will be 6.145 percent in the first year, and by the fourth year, the increase will be 11.25 percent over the old contract.

The defined benefit pension plan will be enhanced and there will be immediate vesting for workers participating in an optional 401(k) program, Carr said. On health care, the contract held the line for the first two years, while there were increases in co-pays and deductibles in the last two years, he said.

Contract negotiations have been relatively uneventful in recent years. The previous two four-year pacts were adopted without a great deal of dissension after a contentious round of negotiations led to a 55-day strike in 2000.

The previous contract between the Machinists’ Local S6 and BIW, a naval contractor and unit of General Dynamics Corp., expired Sunday. The vote on the new contract was conducted at the Augusta Civic Center.

“The negotiating teams did an excellent job hammering out a fair agreement for our employees that will improve our competitive position to secure future work,” BIW spokesman Jim DeMartini said in a statement. “We’re looking forward to carrying on with our Bath Built is Best Built tradition when we come to work tomorrow.”

Local S6 represents 3,200 mechanics, fitters, welders, painters and electricians.

BIW, one of Maine’s largest employers with 5,400 workers, is awaiting a decision by the Navy later this year on contracts for nine destroyers. BIW is competing against Huntington Ingalls Industries for the DDG-51 destroyers the Navy will buy through fiscal 2017.