Louise Patten’s grandfather, Charles Lightoller, was Second Officer on board the ill-fated ship sailing from Southampton to New York in 1912.
He said an order to steer the ship away from the danger was misunderstood, causing the steersman to panic, Mrs Patten said.
At around the time of the disaster, different steering systems were used for steam ships and sailing ships.
Mrs Patten said her grandfather maintained the different systems caused confusion when an order was given to turn the ship to starboard.
She said: “Crucially, the two steering systems were the complete opposite of one another. So a command to turn ‘hard a-starboard’ meant turn the wheel right under one system and left under the other.
“The steersman panicked and the real reason why Titanic hit the iceberg, which has never come to light before, is because he turned the wheel the wrong way.”
Mrs Patten’s grandfather died before she was born but she lived with her grandmother who told her the story.
It inspired Mrs Patten to write a story about the Titanic, in which she makes the claims.
Called Good As Gold, the novel tells the story of a wealthy banker branded a coward after escaping the sinking ship.
She said: “As a teenager, I was enthralled by Titanic. Granny revealed to me exactly what had happened on that night and we would discuss it endlessly.”
Born in Chorley, Lancashire, Mr Lightoller was in charge of the lifeboats on the ship’s port side when it sank.
After surviving the disaster which killed more than 1,000 people, he continued with a career at sea and commanded one of the little ships that rescued British troops from the beach at Dunkirk. – Skynews