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# Whole-ship life raft

Save the whole ship as well as its passengers and cargo
 (+6) [vote for, against]

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.

 — notexactly, Jul 28 2016

Pioneering Spirit https://en.wikipedi...ering_Spirit_(ship)
Mentioned in idea [notexactly, Jul 28 2016]

Volume of 900 Gg of seawater https://www.wolfram...density+of+seawater
Mentioned in idea [notexactly, Jul 28 2016]

Dimensions of sphere and cube having volume of 1.8 Gl https://www.wolfram...=ob&i=1800000+m%5E3
Mentioned in idea [notexactly, Jul 28 2016]

Inflatable boats https://en.wikipedi...iki/Inflatable_boat
Mentioned in idea [notexactly, Jul 28 2016]

PFDs for boats PFDs_20for_20boats
Prior art [csea, Jul 28 2016]

Cool idea. You even did math at us. Croissant!
 — whatrock, Jul 28 2016

Auto inflate rafts are subject to periodic inspection, test and recertification if you expect the manufacturer to stand behind their product. Might be some expense involved.
 — normzone, Jul 28 2016

 — csea, Jul 28 2016

People would just go around with their boats mostly underwater and the air bags inflated, like people drive for miles and miles on that little emergency spare tire.
 — bungston, Jul 28 2016

Anyway, this is a good idea. Better the using several hundred ahem, "glamour" models as the silicon isn't that buoyant, and then the mascara runs...you know how it goes..
 — not_morrison_rm, Jul 29 2016

 hmm, ships don't just sink. Not generally. Before the crucial separation of sea and interior degrades, there are often events. For example, your engine fails. That's not going to be dangerous alone, but you've now lost the choice about which way you're pointing and what direction you're going in. If you're sideways and the ocean gets angry then damage will occur, that could make you sink. Alternatively, you might get driven on to a reef and repeatedly slammed into it. That will make you sink. You may prefer to have a separate craft with some directional control or even a sea anchor to ensure you're in a different place than what is essentially the demolition of a large metal building.

The major one however, is fire. All the floating in the world isn't going to make you want to stay in a fire. You want to be in a different place to the fire, this is steeped in maritime tradition. The ideal location is in a pub, talking about the fire and how you got to be in a different place.
 — bs0u0155, Aug 01 2016

^ There speaketh the voice of wisdom and eperience.
 — 8th of 7, Aug 01 2016

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