There are "air bags" for boats, & they're based on the same premise which you're describing. However, they've never really caught on.
Some of the reasoning is due to the fire issue as you describe. And then there's the "where to stow them" bit. As even deflated, they're not small. Plus, you need to place them somewhere where they can be well anchored, relatively low inside of the vessel.
Both of which, are sticking points which can/will put them in locations where they'd be vulnerable to damage if the vessel is holed, say due to collision). AND... take up a lot of the most premium storage
Plus, if the vessel is holed, & or suffers other major damage, then there's definitely a risk of puncturing them, even if they do do their job. IE; aren't punctured at the same moment/from the same source which holes the vessel. So how much redundancy in terms of air bags does one then buy? And to what "safe" spot do you anchor
Not to mention you need a LOT of bouyancy to float a boat which doesn't already have a fair bit built in. And or is designed with self rescue
in mind from drawing #1 when it's initally designed.
For instance, a boat with extra thick hull
cores, a light keel
, WT doors, & water
ballast - who's tanks
can also act as bouyancy tanks
Keep in mind too, that "float" is a relative term, as if with them deployed, things are awash up to the level of the cabin
house, a vessel wont be very liveable, nor seaworthy
. Particularly in heavy weather
... which is when folks are forced to take to rafts a fair bit of the time. That, or have to live through before rescue
, due to no propulsion
. And thus, are unable to avoid storm tracks. As would also be the case on a 1/2-2/3 awash vessel.
Also, think on how much space down below, several tons in bouyancy bags (inflated) will take up under the best of circumstances. Where then, does one "live" onboard.
And the "kicker". Trying to sell such things, you're having to overcome a few thousand years of nautical practice; Of taking to the smaller boats, when the big one goes down. Even if all of your testing, & studies prove that the new toys work
People think raft
out of cultural programming, & as a last ditch tool to keep the family
safe... or to get the wife to go along on the trip.
Then there would be the upkeep & certification
issues. You have to protect them from chafe & such somehow. Think of all of those little things which can fall/land/be placed atop them, or worse, get in between them & the hull
Along with the re-cert's. Which are done how? Given that they're bolted into the vessel.
And people complain about the cost of raft inspections! Good luck!