Relatives from as far away as Canada praised their brave ancestors during today's ceremony.
Helen Frost from Toronto travelled with her granddaughter Alex Aaronson, six. Alex's great, great grandfather, Artie Frost, 38, was an engineer in Belfast and a member of the guarantee group which Harland and Wolff sent with the ship to record its performance.
Helen Frost said: "It is important to be here because we are very proud of Alex's great, great grandfather.
"He was a brave, brave man and he went down with the ship."
Last night Dr Robert Ballard, who discovered the wreck in 1985, said engineers worked to keep the lights on until the end, helping those in the lifeboats avoid being dragged back towards the ailing Titanic and potentially pulled under.
Mr Frost left four children.
Ms Frost said: "We felt it was important to be here. We are very proud, we have been very impressed, Belfast has done a wonderful job, it is just lovely."
Alister McReynolds' distant cousin William McReynolds, 22, was an electrical engineer on board.
It was his first voyage at sea. He was unmarried and lived in Belfast with his parents.
Mr McReynolds said: "They kept the lights on to the end so I like to think that he was part of that.
"He must have been a forward-looking person as there cannot have been that many of those electrical engineers in 1912."
He said the outlook in 1912, with disaster at sea and the Great War looming, must have appeared very bleak.
"So many people (in Northern Ireland) were biblical Christians, they must have thought that this was the end of the world," he said.
Retired doctor John Martin, whose son Jack unveiled the memorial with more than 1,500 victims' names engraved on bronze plaques, said the ship's doctor, John Simpson, was his great uncle.
A letter penned on board the Titanic by the Belfast doctor to his mother is to be brought back to the city for exhibition.
The letter, from assistant ship surgeon Dr John Edward Simpson, was written on notepaper headed RMS Titanic and brought ashore at Cobh, County Cork. From there it was posted to his mother, Elizabeth, who lived in south Belfast.
Dr Simpson was married and had one son when he took the commission on Titanic. He had previously worked on another White Star Line ship - the Olympic.
In the letter, Dr Simpson said he was settling into his cabin well and that the accommodation on board his new vessel was larger.
John Martin said: "It is the last tangible object that we have from John Simpson, everything else that he had was lost.
"It is the last thing that we know he actually touched, that means a lot to the family."