Turret Awning
Ironclad warship were infamously hot, both because of their metal construction and because, compared to traditional wooden-hulled vessels, they were very poorly ventilated. It was said that Monitor‘s galley reached a temperature of 150° F at times. As a result, most of the crew off-watch spent as much time as possible out on deck, and canvas awnings were set up whenever circumstances allowed.
Therer renders are of the awning fitted to Monitor‘s turret.
Dead Confederates, A Civil War Era Blog 
Dark wooden decks were hot enough, though sailors of the wooden world often went barefoot. Ironclads eliminated that practice, I imagine.