KENNEBUNKPORT — A Rockland-based fishing vessel sank Tuesday several hours after the fishermen aboard called for help.

Plan B, an 81-foot boat, reported taking on water around 7:20 a.m. about nine miles east of Kennebunkport, according to the Coast Guard. The vessel’s pumps were unable to keep up with the flooding and the two fishermen aboard said they were putting on survival suits.

“They thought it was going down a lot quicker than it was,” said Lt. Nick Barrow of the Coast Guard’s South Portland office.

Cameran Lee, a smaller lobster vessel, responded to the Coast Guard’s bulletin for help. It arrived about 20 minutes after the bulletin went out and both fishermen aboard Plan B were able to jump onto it, Barrow said.

The first Coast Guard vessel arrived about 10 minutes later. The Coast Guard sent a helicopter, two rescue boats and a cutter to the scene.

Plan B sank around 11 a.m. in about 300 feet of water, Barrow said. The Coast Guard is investigating the incident, but it appears that a mechanical problem was to blame, he said.

Barrow said the names of the two fishermen were not available and that the Coast Guard normally would not release them.

Plan B was traveling between Portland and Gloucester, Mass. The stern trawler was not fishing at the time.

Coast Guard crews observed a diesel sheen on the water. It’s not known how much diesel was aboard. Barrow said the fuel from Plan B cannot be recovered but that the diesel is expected to dissipate naturally.