Understanding compressed air.

[mylo]

Gotland,

Very impressive. I took

Gotland,

Very impressive. I took a look at your schematic. I wish I understood German.

Mylo.

[don prince]

Gentlemen,

"A boat with 35 KG

[color=#000000]Gentlemen,

"A boat with 35 KG surfaced has the same weight submerged."

Think about this statement! Does this sound logical? I don't think so, and here's why...

Your sub weighs 35 KG setting on a scale on dry land. When your sub is sitting in water, it still weighs 35 KG and hopefully it's floating at the desired waterline. Therefore, the sub will displace a volume of water equal to it's weight... No ifs, ands, or buts!

Now, you begin to dive your sub... Water enters the ballast tank to the point where you reach the state of neutral bouyancy. Your sub has now completed the dive state.

Now, just to prove a point; remove your sub from the water and put it on that scale on dry land. Gusss what? Your sub now weighs more than 35 KG. Where did the extra weight come from? The water in your ballast tank, of course! This ain't rocket science...

I have proven, beyond any shadow of doubt with documentation from the book "Cambridge Ocean Technology Series 2 Concepts in Submarine Design" ISBN 0-521-55926-X, that the Free Flood (FF) surfaces do NOT contribute to bouyance. There are a few exceptions to that as far as model subs... You could use materials that are lighter than water (i.e., a wooden deck), or you could have foam inside the tower (for stability). Other than those exceptions, the FF surfaces don't enter into the equation. And, as far as I'm aware; a resin, fiberglass, or brass object will NOT float and does NOT contribute to bouyancy.

My last recommended book written by a US Submariner; Michael DiMercurio (Nuclear sub experience in the 80's)...

Page 40]



Edited By Don Prince on 1128205000

[don prince]

Gentlemen,

Additional info... The diagram showing

Gentlemen,

Additional info... The diagram showing a sub with external ballast tanks; the weight does stay the same. However, when you blow the external tanks, you lost a considerable portion of your bouyancy. Therefore, the subs static weight will cause it to dive.

The German Type VIIc U-boat had external saddle tanks D2 and D4 that functioned in a similar manor. Plus an external stern dive tank D1, and an external bowl dive tank D5. During a dive all external tanks were blown. The internal ballast tank D3 acted as a quick dive tank. After the U-boat was submerged the internal main ballast tank D3 was blown, to acheive neutral bouyancy overall. The WWII Type VIIc was a fast dive U-boat with a dive time of 30 seconds minimum.

Regards,
Don_

[safrole]

Don, no one is saying

Don, no one is saying the free-flood spaces make any difference. They flood freely, they drain freely. They are not even part of the issue at hand.

Here's a graphic to show you why you're 35kg boat example is exactly right, but also shows that the change in weight you mention is exactly the VOLUME (in grams of water) of the tower.

Take the time to look at it. It's all intuitive and it's simple addition/subtraction. Please tell me why this drawing is wrong and I'll fix it. I really don't think you'll find any credible authority to refute that volume is the deciding factor. There's plenty of respected people here at SC. Maybe one of them can convince you and Jeff, if you still won't believe. I thought Dirk with those beautifully simple equations would have really put it to bed.

[don prince]

You have a sub with

You have a sub with a ballast tank full of air weighing 35 KG, then you have a sub with a ballast tank full of water weighing 35.5 KG. When I went to school back in the 50's, 500 cc of water weighed more than 500 cc of air! Don't you agree? It looks like your diagram does as well.

Regards,
Don_



Edited By Don Prince on 1128211064

[berserk]

Dear Don.

Every boat has it’s

[color=#000000]Dear Don.

Every boat has it’s own weight. Not more, not less. And it don’t change even if you submerge a boat or not. Why? Easily to explain. Because water in the boat has the same density (weight) than the water outside the boat. The one and only difference between surfaced and submerged is the volume. When you submerge your boat, you reduce the volume of it. The boat sinks because you don’t change the weight. If you want to surface the boat, you just have to increase the volume by pump out the water.

Sure, if you take the flooded boat out of the water it weighs more. But, if you add 3 bricks on top of the superstructure, you will see it is even heavier!

Since 1938, here in Germany, we don’t add the water in the ballast tanks to the weight of the boat. But this is very common.

Gentlemen, I don’t know why this is so hard to understand.

About buoyancy. Every material has a buoyancy. Also when it’s heavier than water. Example]

[don prince]

Dear Berserk,

I disagree with your

[color=#000000]Dear Berserk,

I disagree with your statement..

The U-boat; The evolution and technical history of German submarines, Author]

[don prince]

Dear Berserk,

I had to think

Dear Berserk,

I had to think a bit about your steel block (Hmmm)... The steel block will never ever present any positive bouyancy when attached to a sub... It will always be in the very nagative area. Therefore, this does not enter to the equation when we are talking about neutral bouyancy.

It's still an interesting subject.

Regards,
Don_

[berserk]

Don, you wrote it down.

Don, you wrote it down. It's the displacement. What do you think the 189 tons come from? The water? No, it's the displacement of the superstructure.

The "quick dive tank" you're talking about is the "Untertriebszelle". This is used to bring the boat under water when there was a rough sea. Because the waves prevent the flooding of the superstructure. Of course, the Germans used this to submerge faster. But it was not constructed for this purpose. Also the other German boats have this tank.

And more. There was a tank to cover the loss of torpedos (Torpedo-Zelle) but thats not the point of discussion.

[berserk]

I had to think a

I had to think a bit about your steel block (Hmmm)... The steel block will never ever present any positive bouyancy when attached to a sub... It will always be in the very nagative area. Therefore, this does not enter to the equation when we are talking about neutral bouyancy.

Not in the sub, because it's covered from the volume of the sub. It's an example and works only for itself.

[don prince]

Dear Berserk,

I believe the Germans

Dear Berserk,

I believe the Germans were counting the weight of the water in the external dive tanks D1, D2, D4, and D5. They had intake and exhaust valves. The only tank that was open to the sea was the R1 Regelbunker which was a self conpensating diesel fuel tank.

Regards,
Don_

[berserk]

Ok

Ok

[JWLaRue]

Jason/Safrole,

I'm sorry, but your diagrams

[color=#000000]Jason/Safrole,

I'm sorry, but your diagrams don't prove (or disprove) anything. The two 'in water' diagrams show the same "sub" yet we are to believe that one floats and the other sinks?

Besides that perhaps minor mistake in your graphic, all the graphics really do is to re-state what you have been saying graphically.

Two things]

[don prince]

Safrole,

Remember your illustration demonstration that

Safrole,

Remember your illustration demonstration that it didn't matter whether the tower was made of brass, or Foam (although I would suggest resin because foam will float and induce some bouyancy).

The flooded ballast tank weight only had to counteract the remaining bouyancy of the sub. The foam at the waterline, the WTC, and the lead ballast in the keel sets the height of the waterline. In turn, they also counteract the weight above the waterline.

therefore, if the water line is set to a specific height, then the weight of the water taken into the internal ballast tank will submerge your sub.

The displacenent of thicker resin materials Vs thinner brass materials will create a volume displacement difference in the water.

1. This volume displacement does not produce a neutral or positive bouyancy.

2. There may be a difference in the submerge rate, but this would most likely not be noticible in a model sub.

Regards,
Don_

[safrole]

You have a sub with

You have a sub with a ballast tank full of air weighing 35 KG, then you have a sub with a ballast tank full of water weighing 35.5 KG. When I went to school back in the 50's, 500 cc of water weighed more than 500 cc of air! Don't you agree? It looks like your diagram does as well.

Don I don't mean to sound patronizing, but the reason it looks like my drawing agrees with you is that it DOES, and SO DO I!

The submerged boat weighs 500g more. The boat also displaces 500g more. This is counting the ballast tank's volume and weight the way many books do. What's the problem? Can you point to the error?

1. The 35 kg boat took on 500cc water; it now weighs 35.5kg.
2. 500cc of foam tower also went underwater; it now displaces 35.5 liters.
3. The increase in displacement was 500cc, the increase in weight is 500g.

You just need to make the next logical step. (You're very close!) What's so magical about 500? 500cc increased displacement..... 500g heavier boat..... What could it be????

It's the VOLUME OF THE TOWER.
It's the VOLUME OF THE TANK.

IT'S ALL VOLUME, MAN!!!

Anyway please examine those 3 statements. If you understand them well enough to point out a flaw in their logic, you will probably come over to the dark side.

(If you only knew the POWAH of the dark side!!)