wind sail

[wind]

noun Nautical.

a sail rigged over a hatchway, ventilator, or the like, to divert moving air downward into the vessel.

Origin of wind sail

First recorded in 1715–25

The deck lumbered as when we left her, and not a wind-sail up!
Cornish Characters
S. Baring-Gould
An awning was provided, and a wind-sail furnished to conduct fresh air between the decks during the day.
American Prisoners of the Revolution
Danske Dandridge
The huge sunbonnet stiffly swung around like the wind-sail of a ship and stared at the horizon.
From Sand Hill to Pine
Bret Harte
The snow pattered against the cloth stretched like a wind-sail from their flanks to the rising front of the sleigh.
Barlasch of the Guard
H. S. Merriman