Complex sentence: Once the frame had been built, it was normal to cover the ship up and leave it for several months to season but the end of the Seven Years' War meant that she remained in this condition for nearly three years, which helped her subsequent longevity.
Split into simpler sentences: Once the frame had been constructed, it was normal to cover the ship up and leave it for several months to season. However, the end of the Seven Years' War meant that she remained in this condition for nearly three years, which helped her subsequent longevity.