An anonymous donor sailed to the aid of the South Street Seaport Museum with a $500,000 check to repair damage caused by Hurricane Sandy.

The donation made up the bulk of $750,000 in contributions meant to help the museum recover from the storm.

Sandy didn’t damage any of the museum’s ships. But the storm’s floodwater walloped heating, electrical and communications equipment in several of its buildings.

After the storm, volunteers and staff spent weeks cleaning up the museum and its shops.

But officials expect it will still cost $22 million to fix and replace Sandy-ravaged equipment and permanently move building systems to higher floors.

The museum reopened last month, and plans a formal celebration of its post-Sandy re-launch on Jan. 15.

Besides its vessels — which include the lightship Ambrose, the schooner Pioneer and sailing cargo ship Peking — the museum features several new seafaring-related art exhibits.

The storm came at a tricky time for the museum, which was nearly sunk in 2011 by financial and leadership woes.

It’s back on an even keel now that its operations have been taken over by the Museum of the City of New York.