Complex sentence: She only had enough lifeboats to accommodate 1,178 people, only about a third of the ship's total capacity and equivalent to only 53 per cent of those actually on board on the night of her sinking.
Split into simpler sentences: She only had enough lifeboats to take about a third of the ship's total capacity. Had every lifeboat been filled, they could only have evacuated about 53 per cent of those actually on board on the night of her sinking.