Crews early Friday will drill into ledge in the ship channel in Portland Harbor and pack the holes with explosives.

Around 4 p.m., crews will set off the explosives, but the public won’t see or hear much because the blasts will occur 35 feet under water, said Norman Bourque, project manager for Cashman Dredging, the contractor.

The “Kraken,” the drillboat involved in the blasting operation, is a strange-looking vessel that has three drill towers. The vessel is named after a legendary sea monster that is said to dwell off the coasts of Norway and Greenland.

A company video of the Kraken in operation can be found here.

The company will work to remove ledges in five spots in the channel, a process that will take eight days, Bourque said.

The ledges are located in the channel between DiMillo’s floating restaurant and the Coast Guard base in South Portland. Bourque said the ledges are closer to the South Portland side of the harbor.

The explosions will produce some bubbles, he said. When the detonation caps positioned on a board floating on the surface are fired, the public might hear a sound similar to 30 firecrackers going off, he said.

The $9 million project to dredge the shipping channel began last Friday night when one of the nation’s largest dredgers began digging upriver from the Casco Bay Bridge. It is expected to be completed by mid-March.

The dredger stopped operating Thursday because rough seas offshore made it difficult for the company to dispose of dredged sediment, which is carried by a barge to a dumping area about 7 miles east of Cape Elizabeth.

The project, which will assure depths of 35 feet at mean low tide in the shipping channel, is the first maintenance dredging of the channel in 15 years.

Tom Bell can be contacted at 791-6369 or at: [email protected]