In article ,
says...
You stated that subs don't use water for ballast.
I posted a few, out of many, sites that state otherwise.


Dave Doe wrote:
a.
Indeed they do not. They probably use Lead or DU.

Really? Is there a special place in the ocean where
submarines can just scoop up some lead or DU when they want
to dive?

You're just being a pedant aren't you.

What makes a diver sink? - the BCD? Or the weight belt?

The lead or DU is put in the sub at manufacture time, to ensure it is
"heavier than water" (it's overall desnity is greater than water).

Otherwise.. yes they *would* have to find a special place to scoop up
lead, DU, rocks - whatever - to submerge - as their bouyancy ballast
tanks would be ineffective with water in them. You'd have a positive
bouyancy vessel. You can put as much water in 'em as you like - it'd
never sink.

Ostentatious reply expected...

--
Duncan

Dave Doe wrote:
You're just being a pedant aren't you.


No, I am less interested in seeming clever, and playing
semantic games, than I am with simple facts and the physics
that make things work.

What makes a diver sink? - the BCD? Or the weight belt?


Totally different picture. The BCD is a variable volume
device. When the diver inflates it, he is increasing his
displaced volume. That would be similar to attaching a
helium balloon to a sailboat mast for added stability.


The lead or DU is put in the sub at manufacture time, to ensure it is
"heavier than water" (it's overall desnity is greater than water).


Then why does it float when the diving ballast tanks are empty?

Otherwise.. yes they *would* have to find a special place to scoop up
lead, DU, rocks - whatever - to submerge - as their bouyancy ballast
tanks would be ineffective with water in them. You'd have a positive
bouyancy vessel. You can put as much water in 'em as you like - it'd
never sink.


Really? The fact that they're made of steel, and are
ostentatiously lacking in styrofoam, would make it seem
likely otherwise.

Fact- water ballast works just fine.

Fact- any physics used to try & pretend it doesn't must be
false... just like any physics explaining why airplanes
can't really fly... or is that going to be your next hobby?

I do have one suggestion for you.... look up 'metacentric
height' and ponder the relationship of the ceneter of
gravity to the center of bouyancy. It's easier than the
sound of one hand clapping.

DSK

In article ,
says...
Dave Doe wrote:
You're just being a pedant aren't you.


No, I am less interested in seeming clever, and playing
semantic games, than I am with simple facts and the physics
that make things work.

What makes a diver sink? - the BCD? Or the weight belt?


Totally different picture. The BCD is a variable volume
device. When the diver inflates it, he is increasing his
displaced volume. That would be similar to attaching a
helium balloon to a sailboat mast for added stability.

What if the BCD was a solid container (non variable volume device) - and
when the air was displaced it was replaced with water. What difference
would that make?

The lead or DU is put in the sub at manufacture time, to ensure it is
"heavier than water" (it's overall desnity is greater than water).


Then why does it float when the diving ballast tanks are empty?

Because the tanks are not empty, they are full - with air.

Otherwise.. yes they *would* have to find a special place to scoop up
lead, DU, rocks - whatever - to submerge - as their bouyancy ballast
tanks would be ineffective with water in them. You'd have a positive
bouyancy vessel. You can put as much water in 'em as you like - it'd
never sink.


Really? The fact that they're made of steel, and are
ostentatiously lacking in styrofoam, would make it seem
likely otherwise.

You may be right. However are you forgetting they are also full of air
"where the people are" - and furthermore it must be reasonably
uncompressed (don't wanna kill those folk). As I have pointed out - a
sub must have an overall density greater than the water it is in. It
*may be* that the basic production of, makes 'em that way (I've said
that already). If not - they put ballast weight at the bottom of them -
but I admit, I don't know that for a fact. What I do know for a fact,
is that one OR the other MUST be true - or you have a positive bouyancy
"sub" - and it will *never* work - no matter how much water you put in
the bouyancy ballast tanks.

Fact- water ballast works just fine.

That depends on purpose. We are talkiing about *yachts*. How many
yachts use water ballasts vs lead keels? Is there a reason for that?
What's your boat got BTW?

Fact- any physics used to try & pretend it doesn't must be
false... just like any physics explaining why airplanes
can't really fly... or is that going to be your next hobby?

I do have one suggestion for you.... look up 'metacentric
height' and ponder the relationship of the ceneter of
gravity to the center of bouyancy. It's easier than the
sound of one hand clapping.

Yet more reason you'll find lead or DU at the bottom of a sub. (I guess
the thing could be underwater and upside down - damn hard to work in
those conditions though).

--
Duncan