Concur with Don.
Would have been a large incandescent lamp in the fixture (there was a fetish of a sort, back i nthe 60s for mercury-vapor lamps, but that was not common).
MV Tregurtha is called "Queen of the Lakes"--not only the last of the "thousand footers" built, but the longests at 1013'-6". 105 feet wide (max permitted by the Soo Locks).
The Duluth Ship Cnanal is oriented almost due East, and when the wind comes in off the Lake, it will build up a serious fetch which the canal focuses into a serious chop.
The build is progressing nicely.