PORTLAND, Maine — As work gets under way on an eight-month renovation of the Casco Bay Lines ferry terminal, passengers will notice another big change there next week.

A new ferry, the 399-passenger Wabanaki, will join the Casco Bay Lines fleet as soon as Tuesday, Sept. 24, according to Hank Berg, CBL general manager.

The Wabanaki, under construction in Rhode Island since 2011, is the planned replacement for the Island Romance, which was built in 1973 and is the ferry service’s oldest vessel. The Wabanaki is the first new CBL ferry since 2005, when the Aucocisco III was launched.

The new vessel is similar in design and size to its slightly older sister ship, Berg said, and can carry 102 more passengers than the smaller Island Romance. The Wabanaki’s capacity is a reflection of increasing ridership on the ferry service, he added.

Another reflection is the $2.5 million renovation and expansion of the ferry terminal, at the foot of Franklin Street on the Maine State Pier.

At a Sept. 4 groundbreaking, Berg said that when the terminal was constructed 25 years ago, it was built to accommodate 500,000 ferry passengers annually. Today the ferry service carries nearly 1 million passengers to six Casco Bay islands each year.

“We’ve outgrown the capacity of this building,” said Berg, who called the renovation plans “transformative” for the structure. They include doubling the size of the terminal from 3,000 square feet to 6,000 square feet, and moving the waiting area closer to the water, where new windows will allow passengers to view harbor traffic.

Aboard the Wabanaki, passengers will see much that is familiar. Like the Aucocisco, the ship is 110 feet long and 32 feet wide, and is powered by twin diesel engines. From the water, the two craft appear similar, each with a straight bow, a prominent wheelhouse and CBL’s traditional yellow, black and white markings.

But the resemblance is more than cosmetic. The Wabanaki’s similarity to the Aucocisco is intended to make routine operations easier, according to Berg.

“[The Wabanki’s design] allows more commonality in the fleet, and that’s helpful when it comes to things like maintenance and parts,” he said. Still, there are a few innovations, such as more electrical outlets and a dedicated area for carrying freight.

In addition to passengers, CBL ferries carry 5,300 tons of freight and 30,000 vehicles annually.

The Wabanaki’s name should also be familiar. It’s a Native American word meaning “dawn land,” referring to New England and eastern Canada. With the addition of the new vessel, four of Casco Bay Lines’ five ferries bear Native American names with local roots.

In addition to the Wabanaki and the Aucocisco, the fleet includes the Bay Mist, the Machigonne II and the Maquoit II.

The Wabanaki’s name was chosen from submissions by students at the Cliff Island and Peaks Island elementary schools, Berg noted.

Seth Koenig of the Bangor Daily News contributed to this report.