Complex sentence: The high-pressure seawater flooded the lower engine room before the hose was sealed off: it was estimated that if the inflow had continued for another twenty seconds, the weight of the water would have prevented "Dechaineux" from returning to the surface.
Split into simpler sentences: The high-pressure seawater flooded the lower engine room before the hose was sealed off. It was estimated that if the inflow had continued for another twenty seconds, the weight of the water would have prevented "Dechaineux" from returning to the surface.