Whole-ship life raft

Generally, ships carry lifeboats to save their passengers in the event of sinking. These generally work alright for saving the passengers, but what about ship and its cargo? It would be worth trying to save those too if possible, right?

I propose building ships with airbags around the waterline. These would be inflated by gas generators triggered by a signal from the bridge or automatically in the event of a hull breach. They would surround the ship and keep it afloat until it could be taken to a port for offloading and then dry dock for repair.

Regarding buoyant feasibility: The world's heaviest (displacement) ship is the crane ship Pioneering Spirit [link], with a displacement of 900 gigagrams. The volume of seawater having the same mass is almost 900,000 m^3 [link]. That's what needs to be displaced to stay afloat. Let's assume that the entire hull is filled with water, meaning the hull provides no buoyancy. Let's also assume the airbags are only halfway in the water, so their total volume (above and below the waterline) is 1.8 gigaliters. The cube with this volume has side length of only 122 meters [link], which is less than one third of the length of the ship (382 m). So, divide the cube into sixths, and stick three sixths in line on each side of the ship, resulting in 41×61×366-meter airbag on each side of the ship. (This is almost 80,000 m^2 of envelope material per side.) Add a bit more for safety. Totally manageable.

The airbags would need to be resistant to sunlight and saltwater. Such materials are widely used for inflatable boats [link]. It would also be nice for them to be made of a tough enough material to avoid ripping if they collide with anything, but there should also be electric blowers aboard to keep them inflated after the gas generators have done their job, so small leaks won't be much of a problem.

The airbags should be divided into several compartments, or whole separate airbags, for redundancy reasons. Also, to keep the airbags from floating up too high, each one should have an internal truss or tensegrity structure. These will increase the mass (and the gas generators will add mass as well) but it should be well within the capacity of any ship to carry an appropriately sized whole-ship life raft system and still carry almost as much cargo as without one.