Didn't see the movie.

It was my understanding that they thought they had cleared the iceberg when the shup suddenly lurched and there was a gawdawful scraping sound. An underwater section of the berg had sliced a long gash along the Titanic's hull below the waterline.

One of the things that made folks feel confident in the idea that the Titanic was unsinkable was that bulkheads divided the ship into five presumably watertight segments. If they struck a reef or some such thing and one of the segments was punctured, the other four would easily keep it afloat. But a whole string of the compartments were sliced. The ones that were still intact, could have kept her afloat (but tilting a lot). But the compartments were not closed off at the top, and when water filled the ruptured compartments, water spilled over the top into the intact ones.

What sank the presumably "unsinkable" ship was a whole unforeseen domino effect.

Or so I've heard. Your mileage may vary.

Don Firth