Understanding compressed air.

[JWLaRue]

I'm still waiting to hear

I'm still waiting to hear the explanation as to how volume is what matters given these two examples - a sphere that is hollow (think balloon filled with air) and a sphere that is solid...say steel. Both spheres being the same diameter. If only volume matters, why does one sink and the other not?

-Jeff

[safrole]

Jeff sorry I was brewing

Jeff sorry I was brewing that last post before I saw yours. Can I illustrate with blocks? (It's just easier to visualize and to swipe a shape in the design software)

Wife is on me about transcribing a song for band practice tomorrow but I'll work in the other window. Probably within an hour.

I'm glad you stuck in this discussion. I like you Jeff, but you're dead wrong on this one. <grin>

Don, you are mixing the issues. Do like Jeff and present me with a basic problem, the way I've stuck you with a basic one.

Gimme a few minutes.

[JWLaRue]

Some additional references]http://www.fleetsubmarine.com/diving.html

"To get buoyancy

Some additional references]http://www.fleetsubmarine.com/diving.html[/url]

"To get buoyancy right is in theory fairly simple. All you have to do is get the contraption to weigh the same as the volume of water it displaces." See http://www.the-nerds.org/submarine-design-notes.html

"The total weight of the entire submarine must weigh less than the volume of water it displaces in order for it to float.: See http://encarta.msn.com/text_76156726...Submarine.html

"The most basic measure of tonnage is displacement tonnage. This is a direct measure of the actual weight of a vessel. Displacement tonnage is the weight of water displaced by the hull of a boat. A vessel floating in fluid will always displace an amount of fluid equal to its own weight.: See http://www.oceannavigator.com/article.php?a=1315

[safrole]

Listen she's on me, so

Listen she's on me, so I can't do a drawing for you. Plus if the concept of density is lost on you then there's really no hope. Also none of your references contradict the volume argument, except the erroneus fleetsub one we've already discussed. But the sheer volume of links is very impressive, and makes me want to think you're more informed than I am on the subject. And since you are so informed, maybe you can stoop down and explain to a guy like me what I just can't understand.

Can you tell me why these two boats below don't dive? You know Mr Archimedes? He says you can tally up all the underwater parts, and that's your upforce in grams of water. Mr Newton says all the parts above AND below the water have a weight and they are your downforce. Am I violating a principle? If so, can you point out the error, instead of just saying this proves nothing.

Also you may want to address Herr Dirk, as he, like you, seems to know a lot about it.

[JWLaRue]

>>> You know Mr Archimedes?

>>> You know Mr Archimedes? He says you can tally up all the underwater parts, and that's your upforce in grams of water.

While I don't know him personally, Mr. Archimedes says that you tally up *all* the parts (not just those underwater) and that's your upforce in weight. (Pick you measurement system...grams, ounces, etc.)

Your most recent diagrams correctly show what you have stated, but do not correctly represent our favorite Greek scholar.

...and the concept of density is definitely not lost on me! Hence my example of the two spheres.

My examples support the weight "argument"....as in the weight of water displaced......

-Jeff

p.s. not to detract from this discussion, but what kind of band are you in?

[safrole]

Church band, lead guitar, Fender

Church band, lead guitar, Fender (mexistrat) special, Crate VC-30 quad El-84 tube amp, fat tone, don't get me started...

HAH! The bouyant force by our Greek geek is only the parts underwater. N'est-ce pas?

[JWLaRue]

Cool! (re]entire object (in our

Cool! (re]entire[/i] object (in our case a sub) is creating a downforce regardless of whether it's above or below water. In trying to separate the two components (above and below water parts), you are misrepresenting the physics of what is happening.

-Jeff

(ex. trombone and french horn player, who now dinks around on synths)

[yabbie1]

I'm still waiting to hear

I'm still waiting to hear the explanation as to how volume is what matters given these two examples - a sphere that is hollow (think balloon filled with air) and a sphere that is solid...say steel. Both spheres being the same diameter. If only volume matters, why does one sink and the other not?

-Jeff

Because it does not have a model submarine hull to support it!

Put each of those spheres in turn upon your model submarine and adjust the buoyancy of the submerged part of the hull as necessary, or change the amount of lead in the keel, to achieve the same surfaced waterline. This is the actual situation we have.

Doing so in effect cancels out the difference in weight of the sphere "superstructures". Now, when you submerge, they will both displace the same amount of water and require the same size ballast tank.

I have all the books that have been quoted as well as Gabler's "Submarine Design" and can find nothing at odds with the proposition that above-surface displacement is the determinator of ballast tank volume.

On the question of whether to consider the ballast water as extra weight or a reduction in buoyancy/displacement, "Concepts in Submarine Design" (and others) point out that it is "sometimes convenient to treat it one way or the other or even a combination of both". It is really just a convention, though I imagine that if the water is considered an extra weight, it would add to the inertia of the submarine, and affect its manoeuverability.

Yabbie1

[berserk]

I'm still waiting to hear

I'm still waiting to hear the explanation as to how volume is what matters given these two examples - a sphere that is hollow (think balloon filled with air) and a sphere that is solid...say steel. Both spheres being the same diameter. If only volume matters, why does one sink and the other not?

Jeff, are you serious with this. No, you pulled my leg, don’t you?

Jeff/Don. What is your proof? Some websites or books? Take the book from “Ulrich Gabler” (international respected sub constructer) and you will see you’re wrong. This proofed nothing at all. I tried this theory by my self. It works and this is fact.

Jeff, I think it’s unfair to bring up a non working calculation. May your type of calculation was fine for your boat. Someone else builds a different boat and has problems because your type of calculation is wrong. Fill the superstructure of your boat with foam. Lets say the total weight of the foam is 15 grams. Do you really think you just have to add 15 grams to your ballast system? Seriously?

What, in your eyes is a proof? I think you already get this, but you don’t know how to get out of this dilemma.

I think this leads to nothing. Fortunately, some guys know how the wind blows. Respect!

[JWLaRue]

I'm completely serious. Nothing stated

I'm completely serious. Nothing stated by Jason or yourself answers the question for the example that I provided.

You are misunderstanding or misrepresenting the two sphere example if you've assumed that the spheres are attached to the sub. In the example, the spheres are the sub. You cannot possibly answer the question by stating that 'only volume matters'. The merits of your arguments are based on a misunderstanding of Archimede's principle.

Further, if only volume matters....why is it necessary to readjust the trim of a sub (real or model) based on the density of the water?

Finally, how about the words from some well-known folks in the r/c sub field?

Skip Asay, SubCommittee Report, number 15, page 14]heavier[/b] than when it was on the surface."

Matt Thor, SubCommittee Report, number 11, page 46]Archimedes' principle[/i] states that, "the upwards force on an immersed object is equalt to the weight of the displaced fluid." " "....a submarine operates simply by varying its buoyant force. It does this by increasing or decreasing its density by taking on or expelling water within a vessel of constant volume."

(Note bolded text not in the original)

So tell us again how it's not weight, but volume?

At this point, I'm done. Unless you agree to the above, we're going to have to simply agree to disagree.

-Jeff

[skip asay]

I’ve been following this thread

I’ve been following this thread with some amusement (he says with tongue in cheek). It absolutely boggles my mind that this has gone so far and in so many different directions. In the 35 years I’ve been building “boats that sink”, I’ve always tried to keep all the engineering down to it’s simplest application/understanding/etc. In other words, I’m a devout disciple of the KISS Principle.....”Keep It Simple, Stupid”. This thread qualifies as an excellent example of what happens when KISS is thrown out the window.

For over 100 years, marine architects, designers, builders, etc. have listed submarines as having two distinctly different displacements.....surfaced and submerged. When surfaced, part of the sub is out of the water. When submerged, the entire sub is underwater. The difference is actually the VOLUME of everything that is ABOVE the water when surfaced. That volume displaces water and the total WEIGHT of that water that is displaced equals the VOLUME of everything above the water.

Jeff - That is a more detailed description of my SCR #15, page 14 quote.

Safrole - Consider a submarine as an object. To submerge, WEIGHT is added to the object. Whether that weight is in the form of water (obviously the simplest source) or lead or more steel, it is added to THE OBJECT.

And Jeff - I have to agree with Berserk. A block of foam added above the waterline adds virtually no weight but it does increase the displacement which then means that the ballast tank has to be larger by the same amount of VOLUME as the block of foam. True, you could add a compensating amount of lead in the keel but doing so would decrease the height of the boat out of the water when surfaced. That’s a hard one to see, though. Add an ounce of weight to a surface boat or surfaced submarine and, unless the boat is in absolutely glass calm water (or test tank inside the house), you’ll be hard pressed to see any difference. Add that same ounce of weight to a neutrally buoyant sub and you’d better hope the bottom is soft silt!

And Yabbie1 - Norbert is far from being a dummy but a “higher authority” than Archimedes? I don’t think so.

Can we move on now?

Skip Asay

[berserk]

Pappalapapp! Your sphere example is

[color=#000000]Pappalapapp! Your sphere example is useless. Because steel is heavier than water at the same volume. But this is not the point.

The discussion was about the superstructure. Meantime, you’ve got al lot of examples you just ignore. You don’t tell us why “out theory” is wrong. You just only quote some words from others.

Summary]

[berserk]

Hi Skip!

Why you wait so

Hi Skip!

Why you wait so long for this?

[gotland]

Gentlemen

The explanations of Skip are

[color=#000000]Gentlemen

The explanations of Skip are very good, because it shows the relation between volume and weight of water. May be in europe it easer to understand and easyer to calculate with this, because in the metrical system there is a good relation between weight and volume. 1 Liter water is 1 kg, 1000 Liters are also called a ton of Water. 1000 kg are often called a ton of weight.

So if You have 1 Liter of volume on the surface, put in 1kg or 1 Liter of water. For us it's nearly (in practice calculated without earth-accelleration) the same.

What I found out while researching in books about this theme]http://www.subcommittee.com/forum/icon_smile.gif[/img]

Well another anwer to skip]

[subsurface]

I'm no mathematician, but here's

[color=#000000]I'm no mathematician, but here's some thoughts I have

Consider 3 boxes ]