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Pirates of the Caribbean - Underwater boat logical or not?

F

Fango

Landlubber
Anyone who has seen the movie may remember scene where Will and Jack carry a boat underwater. I never got that, but in the shot (as they're carrying it upside down) the water don't go all the way up to inner part of the boat, and they are able to breathe freely.

Can anyone make out the logic in that?
 
They didn't really get underwater, they just use the boat to cover their big heads <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/laugh.gif" style="vertical-align:middle" emoid="xD:" border="0" alt="laugh.gif" />
 
It's a old pirate trick. I've already seen it in a movie with... Errol (not sure). The air is trapped under the boat.
One day I'll try it and say you if it work really.
 
Didn´t they use the same idea in "`diving-bells`" they used to salvage stuff from "Wasa" that sunk near Stockholm? They lowered guy in churchbell shaped thing down. <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/unsure.gif" style="vertical-align:middle" emoid=":?" border="0" alt="unsure.gif" /> This happening in early `17th-century`. If I remember right, they took the guns from the ship using diving bells.

<a href="http://www.vasamuseet.se/Vasamuseet/Vasamuseet.aspx?path=%2fhome%2fvasamuseet%2fom&layout={`C0D465E0-3110`-`436A-A0E4`-EA5BB84475B8}" target="_blank">http://www.vasamuseet.se/Vasamuseet/Vasamu...BB84475B8`}</a>
 
Vassal, you may have wrote it as a joke, but the `before-shot` showed they were underwater. CapitainDams-- that's the explication I saw coming, but how did the air got trapped? I mean, can I experiment it? like take a transparent large bowl and a somewhat `boat-shaped` dish I have here at home to see it I can get it too? I don't know, I still can't see the logic in this until I see it for myself I guess.
 
I'd think that you'd need some heavy weights to pull a boat underwater like that... On the other hand, I can imagine that it would be easier with period wooden rowing boats than with todays glass fiber rowing boats, since the old boats were themselves heavier...
 
Yes, take a simple drinking glass and push it opening down into the water, you will see that the air gets trapped in the glass and if you were a tiny man standing under that glass (or a swimmer who can swim into it) the air would be there for you to breathe.

The trick is negative buoyancy so you can actually carry the boat upside down UNDER the water and still have air to breathe. You'll notice that the glass has some pressure pushing up on it because the air wants to escape. You have to balance the amount of air and the amount of water to get it so that the heaviness of the glass counteracts the push of the air wishing to escape - so you can effectively trap the air under the water in the glass.

That's the same principle of physics used to carry that boat under the water - the combination of the weight of two men and the weight of the boat was heavy enough to easily hold the otherwise buoyant boat upside down under the water and walk with it - and still have air to breathe. <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/onya.gif" style="vertical-align:middle" emoid=":onya" border="0" alt="onya.gif" />

It works! It's very much as Vassal suggests, the diving bell is based off of this principle. If you have access to a bucket (to put over your head) and a swimming pool (so you can get your head and the bucket under the water), you can try it yourself! <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/yes.gif" style="vertical-align:middle" emoid=":yes" border="0" alt="yes.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/par-ty.gif" style="vertical-align:middle" emoid=":cheers" border="0" alt="par-ty.gif" />
 
@Fango : You don´t clean your dishes yourself, do you (be honest)? Else you would have most certainly come across this phenomenon.

The only problem might be that two men don´t have the weight of holding the boat down.
 
Yes, you would need a "negative buoyancy" to get the boat to move like they showed in the movie - the balance of the weight of the men AND the boat (which counts!) against the push of the air wishing to rise to the surface and push the boat up with it.
 
Aye, mates but it's a movie <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/diomed.gif" style="vertical-align:middle" emoid=":dio" border="0" alt="diomed.gif" />
 
<!--quoteo--><div class='quotetop'>QUOTE</div><div class='quotemain'><!--quotec-->Yes, take a simple drinking glass and push it opening down into the water, you will see that the air gets trapped in the glass and if you were a tiny man standing under that glass (or a swimmer who can swim into it) the air would be there for you to breathe.  <!--QuoteEnd--></div><!--QuoteEEnd-->

yeah but notice how it takes more and more pressure u have to apply to the cup when u push it down...imagine a couple hundred pound boat holding it down with all the pressure from the water pushing it back up!
 
Yeah but if you tilt it when dipping it into the water, you will have to use less force to press it down, because there is less positive buoyancy because there is less air trapped.

Continue this to the point until it sinks all by itself to the bottom. Then you will still have air in the glass but actually have to <b>pull it up</b> from the bottom.
 
<img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/bookish.gif" style="vertical-align:middle" emoid=":mm" border="0" alt="bookish.gif" /> Physics is fascinating... <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/onya.gif" style="vertical-align:middle" emoid=":onya" border="0" alt="onya.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/yes.gif" style="vertical-align:middle" emoid=":yes" border="0" alt="yes.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/par-ty.gif" style="vertical-align:middle" emoid=":cheers" border="0" alt="par-ty.gif" />
 
Aye!
BoomSmilie_anim.gif


But chemistry even more so! <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/icon_wink.gif" style="vertical-align:middle" emoid=";)" border="0" alt="icon_wink.gif" />
Saeurebad.gif
 
Heh... Biology was always my favorite. <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/flower.gif" style="vertical-align:middle" emoid=":ty" border="0" alt="flower.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/love.gif" style="vertical-align:middle" emoid=":luv" border="0" alt="love.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/icon_wink.gif" style="vertical-align:middle" emoid=";)" border="0" alt="icon_wink.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/icon_mrgreen1.gif" style="vertical-align:middle" emoid=":cheeky" border="0" alt="icon_mrgreen1.gif" />
 
Ever tip a canoe? Same thing happens. Air is trapped inside, but it floats....Oh and my subject was History.....go figure. <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/bookish.gif" style="vertical-align:middle" emoid=":mm" border="0" alt="bookish.gif" />
 
It doesn't necessarily float. It's all about the <b>volume of air</b> trapped under the boat.

<b>More</b> air: <u>Floats</u>.
<b>Less</b> air: <u>Sinks</u>.
 
If you notice, roughly 2/3 of the slatwood boat contains air. Two healthy men should be able to hold such a a boat under 12 or so feet of water. They only had to clear the immediate waterfront (200 feet, give or take) then swim the rest of the way. Just flip the boat over and let it sink. I doubt anyone would notice the bubbles that far out if they're tending their nets. A bit hard to do with a lobster trap on one's foot, but doable.
 
Heh... Spoken from experience, Mad Jack? <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/icon_wink.gif" style="vertical-align:middle" emoid=";)" border="0" alt="icon_wink.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/laugh.gif" style="vertical-align:middle" emoid="xD:" border="0" alt="laugh.gif" />
 
<img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/icon_wink.gif" style="vertical-align:middle" emoid=";)" border="0" alt="icon_wink.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/rolleyes.gif" style="vertical-align:middle" emoid=":rolleyes:" border="0" alt="rolleyes.gif" /> <img src="http://www.piratesahoy.com/forum/style_emoticons/<#EMO_DIR#>/onya.gif" style="vertical-align:middle" emoid=":onya" border="0" alt="onya.gif" />
 
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