Hundreds of mourners are expected Thursday to celebrate and honor Dennis McGrath, a commercial fisherman and scuba diver who died Oct. 7 in a diving accident in Portland Harbor. He was 56.

Mr. McGrath was a well-known diver on the Portland waterfront for nearly 40 years. He died after being injured while removing line tangled around the prop of the 65-foot fishing boat Jamie & Ashley, which was moored at the Portland Fish Pier on Commercial Street. Police are still investigating the accident.

George Freeman, his longtime dive partner, said Mr. McGrath had done similar jobs 4,000 to 5,000 times during his career. He was an exceptional diver, Freeman said.

“It doesn’t matter how it happened,” he said as his voice trembled. “Let the healing process start now. I’m at his house now. His kids are here. It’s brutal.”

Mr. McGrath, of Scarborough, was married with two children. He was remembered by loved ones this week as a devoted man who worked multiple jobs to provide a good life for his family.

He worked primarily as a fisherman and scuba diver, taking jobs from Massachusetts to the Canadian border. He dove for scallops and sea urchins, went deep sea fishing, and salvaged and sold items he found on the ocean floor. Freeman estimates the pair have used more than 37,000 scuba tanks since 1981.

“Over the course of the years, we could look at each other and know what the other would do,” he said. “We were the worst thing that happened to sea urchins and scallops. We were really methodical. We made a good living on the ocean for many years.”

Jim Buxton, another fisherman and commercial diver who rushed to the pier after the accident, said Mr. McGrath was well-known on the waterfront.

“He was like an institution,” Buxton said Wednesday. “He made a living diving for sea urchins and scallops. When you are scallop diving, you need to be able to read the bed of scallops and understand with a compass and the direction of the tide, where you’ve been and which direction you should work. He was very good at that.”

Family and friends this week recalled Mr. McGrath as a positive, honest and happy guy who had a passion for life.

Steve McGrath of Fort Lauderdale, Florida, said his brother was thoughtful and kind, the type of person who rarely said no to anyone.

“There are 10,000 stories out there about Dennis,” his brother said. “Dennis was a lot of things, but he was never boring. We went on a lot of ski trips. Dennis would pack a half-dozen lobsters and 5 pounds of scallops in his carry-on. He would make them up that night, saying he caught them that morning. More than any person I’ve met, Dennis lived for today. Not next week or next year. He spent every day, focused on the day.”

A GoFundMe page was created to help raise money for Mr. McGrath’s family. As of Wednesday, more than $26,000 had been raised.

Visiting hours will be held from 5 to 8 p.m. Thursday at A.T. Hutchins Funeral and Cremation Services, 660 Brighton Ave. in Portland.