Complex sentence: Lifeboat 1 had overturned as it was being lowered, spilling its original occupants into the sea, but it managed to right itself shortly afterwards and was later filled with people from in the water.
Split into simpler sentences: Lifeboat 1 had overturned as it was being lowered, spilling its original occupants into the sea. However, it managed to right itself shortly afterwards and was later filled with people from in the water.