I was wondering how long that coating would hold when it
s in use. Knowing that WB used it to get to Marineford and that its able to at least bring the ship over FI to the NW gives the coating a rly large radius, but i guess that coating can`t be used much further than that.
We saw that the bubbles burst when they`re leaving a specific radius around Shabondy and my idea is that the coating also bursts when it reachs a specific radius(which is sure much further than a normal bubble).
That points towards the fact, that the coating gets more and more weaken over the time(and as further away from Shabondy), which makes it being more prone to burst.
So in the beginning it may be not harmed much by swords or other solid things going trough the surface, but further away even smaller things going trough the surface could make it burst..
So thats why it`s dangerous to have a bad coater, because then the coating is already rly weak at Shabondy(just a rly thin layer) and thats why many die after being underwater.
The coating bursts because something goes trough the surface.
(i guess sea monsters are always hard to handle and a real threat)
I've been wondering about that too. My take is that the coating will function like the octopus balloon they rode down from Skypiea. After a certain distance from fishman island, it will weaken abruptly and pop. Marineford is so close to the entrance to FI that I don't think distance was particularly relevant for Whitebeard's armada. The coating looks to be fully operational on the Moby Dick when it emerges in the bay (Ch 551 p 16).
The bubbles on Shabondy already made that impression that they had a rly large amount of fresh air stored in them.(Charlos using it as a helmet for a long time, Luffy in that bike-bubble,etc)
So such a huge bubble like the ship has now sure contains a huge amount, which will be enough for a few days..also like already said the TS still has some plants which create oxygen for the case of emergency.
Regarding the air concerns… I wouldn't worry about it. That bubble over their heads is pretty big, and you really don't need many plants to generate enough oxygen for such a small crew:
Uhm… I hate to state the obvious on this one... but land plants don't photosynthesize well in pitch black underwater depths, so you're not going to generate O2 that way. It's certainly possible that Oda will put in a super powered plant, like the ones from Hercules' island that don't need to abide by the rules of conventional reality, but a standard garden ain't gonna do the trick.
I don't think we can use the bubble bikes as a comparison because all had tubes going in and out that may have functioned for gas exchange into the environment. However, Carlos was wearing either an air filtration or O2 supply backpack as part of his spaceman getup, so I suppose the same technology could be applied here.
The problem wouldn't be lack of oxygen so much as a build up of CO2 as a waste product from all the animals and plants on board. CO2 poisoning can be pretty nasty, leading eventually to coma and death. Even given the size of the bubble, the build up of toxic gases would be fairly quick. As in measured by hours, not days.