What’s that three-legged thing out in the water?

A mysterious vessel, visible from New London’s and Waterford’s coastal areas Friday, showed up in the waters of Niantic Bay on Wednesday.

The floating platform may easily be mistaken for an oil rig, but the reality is much cleaner.

Energy companies Eversource and Ørsted will use the vessel to help construct an offshore wind farm 35 miles off the coast of Long Island, spokesperson for the Ørsted and Eversource partnership Justin May said Friday.

The joint project, known as South Fork Wind, will provide 130 megawatts of energy, enough to power 70,000 New York homes, May said.

The vessel, called the L/B Jill, belongs to Seacor Marine, a marine transportation company that provides “safe, reliable and diverse transportation services to offshore energy facilities around the globe,” according to their website.

The L/B Jill will stay docked off New London’s coast until Monday to avoid incoming bad weather as it continues to its project site, May said.

On Monday, it will continue to the project’s location, a federal lease site approximately 19 miles southeast of Block Island, R.I., and 35 miles east of Montauk, Long Island, according to the website for the Bureau of Ocean Energy Management (BOEM), which approved the lease.

On Jan. 18, 2022, BOEM approved a Construction and Operations Plan for the project at that location and accompanying South Fork Cable Project, according to their website.

The L/B Jill is a lift-boat, a class of boat that features a large platform which can be lifted out of the water via long “legs” that reach down to the sea floor, May said.

“The Jill will be used to provide an accommodation and gangway platform for the commissioning of the project’s offshore substation,” May said.

Subsea cables will connect the offshore turbines to the offshore substation, then the offshore substation to a substation on land where the energy will enter the electric grid, May said.

d.drainville@theday.com