Much has been said about the funnels onboard the Titanic.We know from drawings and technical data that the fourth funnel was a dummy but why.
As was usual at the time the appearance of the ship was of great importance,it had to look good in real life,and in advertisments to give the impression of stability,speed and safety.
Consequently the proportions of the ship were important and for a ship the Size of the TITANIC three funnels would look too few so a forth,and false funnel was added behind the three real funnels.Of course in advertisments illustrations falsely took licence to show smoke coming from the four funnels.