The yard is a part of Fincantieri Marine Group, which is Italian shipbuilding company Fincantieri's US subsidiary.
The shipbuilder held a private keel-laying ceremony on 25 June at his Sturgeon Bay shipyard in Wisconsin to mark the formal start of the vessel's construction.
Fincantieri said it did several months of pre-fabrication work before setting up the 55-ton assembly for the vessels.
Northstar, backed by Oaktree Capital Management, founded Polaris, and ordered last year's LNG bunkering barge.
The owners will name the 103-meter long vessel "Clean Canaveral". When delivered it will work along the US East Coast as an articulated tug and barge service.
The 5,400 cbm vessel will feature four Type C tanks and a Wartsila Finland cargo handling system.
Fincantieri expects the LNG bunkering barge to complete in late 2021.
Maritime Business World