Lindblad Expeditions is expanding its reach into the Arctic with plans to grow its National Geographic polar fleet on heightened demand.

The Sven Lindblad-led owner has signed an agreement with Norwegian shipbuilder Ulstein to build a new polar vessel, enlarging the flotilla to four ships in the third quarter of 2021.

The expansion will follow launches of 100-berth National Geographic Quest in July 2017 and 100-berth National Geographic Venture in December 2018.

The newest ship will accommodate 126 passengers in 69 cabins and feature Ulstein's X-Bow hull design for greater fuel efficiency.

It will sail as the sister ship to National Geographic Endurance, to be delivered in the first quarter of 2020.

"National Geographic Endurance ... has been met with considerable excitement from both our existing guest community and those new to Lindblad-National Geographic," chief executive Sven Lindblad said.

"We are confident that its sister ship will garner the same level of enthusiasm in the market."

The ship will be "fully stabilised with the highest ice class (PC5 Category A) of any purpose-built passenger vessel," the company said.

“These two ships will represent a whole new level of capability in expedition cruising, in terms of the level of comfort they provide guests, the regions and itineraries they are able to travel to and their ability to act as platforms for science in some of the most remote and pristine parts of the world,” Lindblad said.

In 2017, the original order at Ulstein came with two optional ships.

The first newbuilding cost a reported NOK 1.1bn (then $134.6m).

A fourth ship in the polar series was announced last year, but no yard was given for the deal.

"These new polar vessels are the next step in the long-term growth of the company, and enables us to capitalize on the substantial demand for our polar expeditions," Lindblad said.

Quest offers itineraries to Alaska, Belize, Costa Rica & Panama, Pacific Northwest, while Venture sails to Alaska and Baja California.

Lindblad, whose entire fleet includes nine National Geographic ships and five other passengerships, has yet to disclose the name and sailing areas for the newest ship on order.

The company did not indicate what type of fuel its ships burn in arctic regions but VesselsValue shows that Quest and Venture are not equipped with exhaust gas scrubbers.

Ulstein Group chief executive Gunvor Ulstein called Lindblad a "highly competent and experienced customer" with which it looks to continue a "good and constructive" business relationship.

Closer to profit

New York-based Lindblad has come closer to posting a profit, thanks to a multimillion-dollar tax break at the end of 2017.

The company reported a $4.6m net loss for the fourth quarter , improving on a $16m loss during the same period last year.

Those results led to a $0.10 loss per share versus a $0.36 loss per share a year ago, beating Wall Street consensus by $0.01.

Bottom-line results benefited from a $13.1m tax cut during last year's fourth quarter as a result of US Tax Cuts and Jobs Act.