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Comment by mrfusion | Hacker News Reader

What about the scene from pirates of the Caribbean where they walk underwater in an upside down rowboat. Is that realistic?

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Because CO2 dissolves well in water, diving bells work much better than intuition says them should.

But then, I'd expect the boat to break much sooner than they get out of air, or even completely under water.

If you're asking about the oxygen levels, I'd say so. At a rough guess of 1m^2 of oxygen per person in the boat, for two people. That's an hour of walking according to the article. (Assuming water takes less oxygen to walk in)

I think it'd float to the top though. It'll need some kind of weight...

A one ton metal boat shaped object would do:

http://kwc.org/mythbusters/2007/11/episode_92_pirates_2_row_...

The CO2 buildup would kill them long before they reach the 17.5% O2 mark. And considering how hard it is to actually walk in water, i'd say it would almost be equivalent to working out. According to the article, a person that is heavily working out would have 10 minutes to reach the 17.5% mark in a 1m^3 area. So maybe 20 minutes for the boat people? And that is neglecting the CO2.

Except both oxygen and CO2 diffuse in and out of water so that buys you time, especially if the water current is constantly keeping the concentrations equalized near the boat.

Nitpick: s/1m^2/1m^3

> I think it'd float to the top though. It'll need some kind of weight...

A simple way of thinking about it is that boats float because they contain air (rather than water). The fact that they are upside down or the right way up changes little.

Since the rowboat can support two people, it should definitely float to the surface, dragging them along with it.

> Since the rowboat can support two people, it should definitely float to the surface, dragging them along with it.

Only if the air bubble occupied the entire inner portion of the hull. If it were, say, only half the volume of the hull - I suspect it would be neutrally buoyant with the weight of two people.

People are roughly* neutrally bouyant in water. Thus they don't weigh anything when submerged. Otherwise swimming would be very hard indeed. So you would need to weigh down the boat to sink all that air and wood.

*depending on depth and body composition, but give or take a bit, neutral.

Agreed, but boats when not filled with air are typically negatively buoyant. I'd wager that there's an air bubble small enough to make the whole system negatively buoyant, but large enough to sustain the people breathing it for some period of time.

The first diving bells didn't have a system to refresh the air supply, they were still used for meaningful work.

https://en.wikipedia.org/wiki/Diving_bell

They tested this on mythbusters- http://www.discovery.com/tv-shows/mythbusters/mythbusters-da...

Well there was that cook who survived for 3 days in an air pocket inside a sunken fishing boat. At the time there was a lot of discussion what made that possible. I believe it was posted to HN as well but can't find it:

http://www.huffingtonpost.com/2013/12/05/cook-survived-sunke...

Works fine in a universe that allows for magically undead pirates....

Not even in the slightest. Yes, i understand this was probably a joke, but still. That scene was pretty dumb.

Actually there's nothing dumb about the scene, except that there would be an upward pressure on the boat (buoyancy).

If that was overcome (e.g. with some weights or strings holding it down), it would be perfectly fine to breath in there for a while.

So, aside from the buoyancy issue, not only it's not "dumb", but that's exactly how old "diving bells" worked.

https://en.wikipedia.org/wiki/Diving_bell

Really... you take issue with some exaggeration in buoyancy physics over the undead pirates?

It's pretty normal to be more bothered by casual violations of the way the world works than by fantasy elements. It's similar to the Uncanny Valley. With fantasy elements, our suspension of disbelief allows us to accept them as part of an alternate set of rules for the world. But when a part of the movie that seemed to be the same as the real world suddenly behaves differently, that can be off-putting and feel inconsistent. For example, if a character couldn't carry a small bucket of water but could carry a large man, many people would read that as an inconsistency rather than just accepting it.

I hate this argument. Fantasy movies are expected to be internally consistent. That means they follow the fantastical rules they set down, and they otherwise follow normal real-world rules.

(Though I agree with coldtea that the PotC scene wasn't that bad.)

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