Cowls are descendants of simple vent pipes on sailing ships, cousins to the famed Charley Noble over the galley. When ships acquired engines below, the need for air down there became acute.

Eventually, somebody decided that the pipes could be made to extract fumes more efficiently or even direct air below. Hence, the hood-like cowl. On working ships, they usually were made of welded-up galvanized steel, which if done properly can last for years and require no care.

When cowls migrated to yachts, they were made of spun brass with red or white throats. Later came chromed brass and then stainless. They are more often now made of flexible PVC.…