Understanding compressed air.

[subsurface]

I made a mistake, I

[color=#000000]I made a mistake, I meant to say ]

[don prince]

Good afternoon Gentlemen,

First, I would

[color=#000000]Good afternoon Gentlemen,

First, I would like to apologise for any remarks that may have seemed harsh. I guess we all get tired and defensive. I did some yard work this morning and lets try this again refreshed...

Now to the last Item up for discussion; The Volume of other structures, other that the pressure hull. Again my bible...

Bouyancy Elements]



Edited By Don Prince on 1128285722

[safrole]

Jeff you're wrong about Archimedes.

Jeff you're wrong about Archimedes. Things in the air don't displace any water, so they don't increase bouyancy.

Subsurface, you are correct. My box drawing allows you to easily see the necessary water that must be added. It also allows you to see that it is exactly equal to the VOLUME of the tower.

The math isn't even algebra, it's addition and subtraction. If anyone can point out an error (Jeff I'm looking in your direction) I will fix it, eat my hat, whatever.

Let me paraphrase Archimedes.

"A conning tower under water is bouyed up by a force equal to the weight of the VOLUME of water it displaces."

Throw in a litre of lead or hold under a litre of foam, both are bouyed up by a kilo of force. The lead sinks because a single kilo of bouyancy (upforce) cannot overcome its large weight and the other has to be held under because a kilo of bouyancy would push it right out of the water, but they are both BOUYED UP BY THE SAME FORCE, 1 KILO. THEIR WEIGHT IS IMMATERIAL; THEY BOTH GET 1 KILO OF UPFORCE. Never argue with an ancient Greek. They are already dead and you'll be dead wrong. But how does this apply?

1. So as a conning tower goes under water, it changes the overall bouyancy of the boat by the weight of the VOLUME of water it displaces.

2. When the boat is at submerged equilibrium, this increase in bouyancy exactly makes up for the decrease in bouyancy (or extra weight you gained, if you prefer) from flooding the tank.

"How much water weight did you take on to achieve this new submerged equilibrium?"???

I'm glad you asked. Well, it obviously has to be an amount of water weighing the same as the new bouyant force from our recently submerged tower. Archimedes said that the new bouyant force was the weight of water displaced by the tower, so I bet the water we should take on board would be the same VOLUME as that displaced by the tower, since two identical volumes of water should exert the same force. **BLING BLING BLING **

If you were following well until that last sentence, you are probably too set in your ways to learn something new, and should familiarize yourself with the concept of antiprocess

Skip, this is what happens when know-it-alls collide, useless academic debate. There's plenty of other threads if people find this one useless, but I find this one very engaging. We also appear ignorant to the non-English modellers when we promote dumb ideas. They've already settled this on their boards, I assure you. Dirk came over here for his FIRST post and try to share some knowledge, but some of us couldn't receive the truth, too set in our ways to weigh both sides and make a fair decision. Talk about casting your pearls before the swine. I wonder if he'll be back. (I hope so.)

And what about Dirk? I suppose Captain Equation proves nothing? Please. There's none so blind as he who will not see. That said, please point out the error in my cheesy little box drawing. I guess I should at least entertain the possibility that it could have an error.

[don prince]

Safrole

The only problem with your

Safrole

The only problem with your line of thinking is the tower does have a certain amount of bouyancy... BUT, the material that is used to construct the tower is MORE dense (resin, fiber glass, or brass) than the water surrounding it. Therefore, we don't need extra water (weight) in the ballast tank to compensate for the towers negative bouyancy factor.

Regards,
Don_

[gotland]

Safrole, Berserk, Yabbie1, Eloka, Mylo

Safrole, Berserk, Yabbie1, Eloka, Mylo and hopefully Skip,

I believe now we get at this point af the discussion, where it's not anymore a problem explained by Archimedes, those are problems Plato and Aristoteles thought about

Gotland

[subsurface]

I remember a high school

I remember a high school experiment that we did nnn years ago - hehe.

The experiment was concerned with volume calculation and "relative" density. It was a long time ago, so please forgive me if I'm a bit vague.

Take a measuring jar and put water into it up to some level that is indicated on the jar. Now put an object into the jar.
The water rises by some amount and this gives you relative density (If I remember correctly) - and thus exact volume.

If you have a sub already setup at a specific waterline, then pushing the sub (with your hand) completely below the surface of the water will raise the water level by the amount that you would have to pump into the sub using a ballast system.

I guess the only problem with this is that they don't make measuring jars big enough and you'd have to already know volume levels (between each marker) for your specific container.

I guess this could be done by slowly filling an old bath tub with water from a 1 litre bottle and putting marks (ie lines) that indicate every 50 litres or something like that.

Then you put your sub in with the water. Record the current water level when it's floating (at correct waterline).

Then push it under and record the new level. The water required to get the sub under should be the difference.

This then leads me to believe that this is in fact a volumetric problem more than anything else, or at least that the calculations are volumetric.

[safrole]

Subsurface you are EXACTLY correct

Subsurface you are EXACTLY correct I believe. You show the change in displacement, a volumetric difference.

Don, your concern about the density of tower materials and Jeff's challenge to explain why sphere's of metal and foam will either sink or swim (though their displacement is equal) probably come from a common line of thinking.

Do you understand that a block of foam and a block of cement have the same bouyancy? It's absolutely true.

"A body immersed in liquid is bouyed up by a force equal to the weight of (THE VOLUME) of water it displaces." Nothing about the weight of the body in that statement. 1 liter of steel and one liter of air have the same bouyancy, 1 Kilogram. One sinks, one floats; that has nothing to do with their bouyancy. Underwater they both displace a liter, they both have a kilo of bouyancy.

A resin tower, a foam tower, or an "air" tower (strange concept, maybe a clinging bubble to the top of the hull) all have the same bouyancy, if their volumes are equal. Do you agree?


Now... (here's the big leap - take a breath )

When the boat dives, the water weight it takes on equals the weight of water displaced by the tower. Was it a foam tower, and air tower a metal tower? DOESN'T MATTER.

But, but, but... DOESN'T MATTER. When the tower went under, it increased the displacement of the boat. I think I can say we ALL agree on that. How much? Careful... the material of the tower does not matter. Steel, foam, kryptonite, it DOESN'T MATTER. Whatever new volume just went underwater, that is the increase in the boat's overall volume (displacement).

If I can get you to agree that how ever much VOLUME of tower went underwater is exactly how much the boat's overall volume has increased, then I've got you hooked. But don't be afraid to agree, it's the right way.

Look up at the three examples. If they were towers, each of them upon diving would add one liter to any boat's overall volume, right? The material doesn't matter for that. If you want a boat to remain in equilibrium upon diving, yet it's volume will be one liter bigger (tower underwater) then how do you compensate? You lose a liter of bouyancy, or as you guys seem to prefer you take on a kilo (liter) of water. Even though these towers are all different weights and therefore densities (resin, metal, etc.) they all add a liter, they all add the SAME VOLUME and it is this volume for which we compensate with ballast water.

[don prince]

Dear Berserk,

I think we are

[color=#000000]Dear Berserk,

I think we are saying the same thing... I will comment your excellent posting.

Summary]

[subsurface]

I think I omitted something

[color=#000000]I think I omitted something important in my last post.

It certainly did seem to me that the problem appears to be volumetric. But then I though about it some more, and re-read my post.

I said ]

[don prince]

Gentlemen,

I really don't think this

Gentlemen,

I really don't think this discussion is anything but good... I have learned to appreciate and respect others opinion on this subject, and a different prospective. I have had to do a great deal of reading and reasearch to better understand this subject. This has been a learling experience for me...

Best regards,
Don_

[gotland]

@ Subsurface]http://www.subcommittee.com/forum/icon_biggrin.gif

@ Don and

@ Subsurface]http://www.subcommittee.com/forum/icon_biggrin.gif[/img]

@ Don and Safrole]http://www.subcommittee.com/forum/icon_biggrin.gif[/img]

Gotland

[gotland]

@ Subsurface]http://www.subcommittee.com/forum/icon_biggrin.gif

@ Don and

@ Subsurface]http://www.subcommittee.com/forum/icon_biggrin.gif[/img]

@ Don and Safrole]http://www.subcommittee.com/forum/icon_biggrin.gif[/img]

Gotland

[safrole]

Gotland, I would agree about

Gotland, I would agree about human philosophy, which is why I posted the link on "antiprocess". Even though the discourse is pretty friendly.

I also agree that it takes equal force pushing down in Subsurfaces bathtub experiment.

A one-liter bubble or a one liter brick on the back of your sub, and it will take a kilo of force to push it under.

[subsurface]

Yes - See it now,

The

Yes - See it now,

The density only matters when trimming the waterline. Submerging is then a volumetric problem.

thanks guys.

[berserk]

I say the ballast tank

[color=#000000]I say the ballast tank has taken in 500 cc of water and the weight of the sub has increased by that amount.

Your decrease in volume is exactly the same as the weight taken into the ballast tank. For example]

Don, I agree in this. But, I'm thinking about a real sub. This sub has a ballast tank which is open to the bottom. If you open the vents, the water floats in and destroys the displacement. Now take your glass. Flip it upside-down and bring it to the water. Assumed the glass has a hole in the bottom. The air in the glass prevents the glass to sink. Now we open the hole, water floats in and the air is blown out. The glass sinks. We have now a flipped glass with water in it. Does this glass weigh more now?

See, since 1938, here in Germany is this point of view very common. Because its easier to handle and to count with.

I’d liked this discussion and I thing it helped to brush up knowledge!

Haut rein Jungs!