Since the introduction of steam-power to ships in the 19th century, the funnel has been a distinctive feature of the silhouette of a vessel, and used for recognition purposes.
The required funnel cross-sectional area is determined by the volume of exhaust gases produced by the propulsion plant.
The Southampton, Isle of Wight and South of England Royal Mail Steam Packet Company has traded under the name Red Funnel for most of its 150+ year history.
Intended as an aerodynamic aid to keep exhaust clear of the deck the modification had very little practical effect but was retained because it made the four ships of the class immediately recognisable and gave Cunard a suitable modern image.
There was a trend for 'designer funnels' on liners in the 1960s as fashion and aerodynamic advances combined to offer designers more options that the traditional cylindrical smokestack.
Although they can reduce top-weight, they have not gained universal popularity due to the problem of exhaust gases corroding electrical aerials and equipment.