Buoyancy - 'proper' weight check

Is there a 'proper' way to make a buoyancy check?

In a pool- no suit, full cylinder, no air in BC, I descend when I exhale.

I'm told I should carry 2kg to balance the air used but then I have to keep
adding/removing air to maintain negative buoyancy at various depths.
Without the weight I have no problem and can control depth with the lungs.

Cheers

makem

Try not carrying the extra 2 kg. Make it 1 kg instead or none at all. I can
compensate the equivalent of 5 kg just with my lungs.

"makem" <makem@home.com> wrote in message
news:Xns948014EF62C50makemhomecom@194.117.133.134. ..
> Is there a 'proper' way to make a buoyancy check?
>
> In a pool- no suit, full cylinder, no air in BC, I descend when I exhale.
>
> I'm told I should carry 2kg to balance the air used but then I have to
keep
> adding/removing air to maintain negative buoyancy at various depths.
> Without the weight I have no problem and can control depth with the lungs.
>
> Cheers
>
> makem
>
>

> In a pool- no suit, full cylinder, no air in BC, I descend
> when I exhale.
>
> I'm told I should carry 2kg to balance the air used but then
> I have to keep adding/removing air to maintain negative
> buoyancy at various depths.
> Without the weight I have no problem and can control depth
> with the lungs.

Take a near-empty tank (15-20 bar)
Set your kit up.
Get into whatever environment you're going to be diving in, wearing whatever
you would normally wear to dive it.
Get all the air out of the BCD.
Add weight until you can sink by breathing out and resurface by breathing
in.

If, with a near-empty tank, you can do this with no weight on, then you
don't need any lead.

Iain

makem wrote:
> Is there a 'proper' way to make a buoyancy check?

Ohh my favorite subject..
<fx: everybody clicking "next unread">

What is the object of correct weight?
To get down and to stay down.
When do you need the most weight?
At the end of the dive with the tank empty?
Is that 50bar?
No it's empty. What good is there carrying a
reserve if when you try to use it it pops you to
the surface? There is air on the surface so
you don't need the reserve then.
I don't fancy diving on an empty tank...
Don't worry.

How much air is there in a tank?
230 bar or so I hope...
No weight. Try these numbers.
232bar in a 12L tank is 3.3Kgs of gas.
300bar in a 10L tank is 3.3Kgs of gas.
If you have different tanks factor by volume.

So with a 12L I must be 3.3Kgs overweight at
the start of the dive. So how do you measure it?

Well the PADI deep breath is eyes level is quite
good but a lot of people can't read 'deep' and just
breath in when you need to breath in pause breath
in some more. This leaves a lot of people under
weight.

The best way is in the pool. Full kit. That's every last
buckle, clip and your thermals. Fill the jacket and then
empty it in the water so if it does have any air traps
they are trapping air. Lie on the bottom at the shallow
end with weights in your pockets and see how many
you can place on the bottom and still go up and back
down again (horizontally). Note this number.

Note the SPG and the tank pressure and work out how
much weight of gas you are carrying. Note this number.

Now go home. Wait until everybody is out. Put the full, yes
I said full, kit back on. Stand on the bathroom scales.
Weight in Kilos please.

Right so how do we work things out?
Take the amount of weight you needed in the pool plus
the weight of gas in you tanks when you did the test
and that is the amount of weight you need in fresh water.
Take your total body and gear weight, including the
newly calculated fresh water weight belt and multiply that
by 0.027 and add that extra weight for use in sea water.

That's exact.
Now you see why we all use the PADI trick diving a single?

PS: Take your weights and put them on the kitchen scales.
I did this and discovered while the new ones were as expected
the old ones were all over the place so I stamped numbers on
them.

nigelH

In article <Xns948014EF62C50makemhomecom@194.117.133.134>,
makem <makem@home.com> wrote:
>Is there a 'proper' way to make a buoyancy check?

It depends on what you mean by a buoyancy check.

>In a pool- no suit, full cylinder, no air in BC, I descend when I exhale.
>
>I'm told I should carry 2kg to balance the air used but then I have to keep
>adding/removing air to maintain negative buoyancy at various depths.
>Without the weight I have no problem and can control depth with the lungs.

The air in your cylinder might well weight 2Kg, so you really ought to
do this check with as near empty a cylinder as possible.

And you ought to be doing it with the full kit you need for the
environment you'll be diving in. Ie. Pool or open water, doubles, singles,
lightweight wet suit (for the tropics) or heavyweight semi-dry or dry
suit for this country, fresh or salt water.

Eg. In general, you'll need an extra 2Kg (ish) to offset the bouancy
change when moving from fresh to salt water, and you might not need
any lead at all in a pool, but with full diving suit, you might need
10-14Kg of the stuff! (or next to none if you have doubles and a SS
backplate), etc.

Gordon

"Nigel Hewitt" <nigelh@REMOVETHISnigelhewitt.net> wrote in news:bvdabi
$qnq$1@hercules.btinternet.com:
snip>
> Well the PADI deep breath is eyes level is quite
> good but a lot of people can't read 'deep' and just
> breath in when you need to breath in pause breath
> in some more. This leaves a lot of people under
> weight.
>
> The best way is in the pool. Full kit. That's every last
> buckle, clip and your thermals. Fill the jacket and then
> empty it in the water so if it does have any air traps
> they are trapping air. Lie on the bottom at the shallow
> end with weights in your pockets and see how many
> you can place on the bottom and still go up and back
> down again (horizontally). Note this number.
snip>

No suit:

> 'Padi deep breath' - I go down, no weight

> 'Lie on the bottom at the shallow
> end with weights in your pockets and see how many
> you can place on the bottom and still go up and back
> down again (horizontally)'

I get on the bottom without weights - and can still go up and down.
It appears to me that this works for me only if suited.

It would seem that for me, without a suit 'the cat dit it' and ian
appear right - no weight needed in the pool for me.

Many thanks ppl :)

makem

makem wrote:

> It would seem that for me, without a suit 'the cat dit it' and ian
> appear right - no weight needed in the pool for me.

If your tank is negative when empty, you may actually still need to drop a
bit of lead. If your tank is bouyant when empty, you probably need to add a
bit, or you were overweighted before (quite possible to do without
noticing). If you tested in fresh water and dive in salt water, you still
don't know if you've got it just right.

Lee

Minor pedantic point, speaking as a novice diver, but has-been
(not-very-good) mathematician:

> Now go home. Wait until everybody is out. Put the full, yes
> I said full, kit back on. Stand on the bathroom scales.
> Weight in Kilos please.

It's slightly easier to merely carry your gear onto the scales.
No real need to actually wear it in the house after all
And you can even weight it in batches and add the numbers up.

Rest of post seems OK though.

Sorry

Hywel

Hywel & Ros wrote:
> Minor pedantic point, speaking as a novice diver, but has-been
> (not-very-good) mathematician:
>
>> Now go home. Wait until everybody is out. Put the full, yes
>> I said full, kit back on. Stand on the bathroom scales.
>> Weight in Kilos please.
>
> It's slightly easier to merely carry your gear onto the scales.
> No real need to actually wear it in the house after all
> And you can even weight it in batches and add the numbers up.

But that's no fun to write. Anyhow have you ever tried to stand on
the scales clutching your dry suit, thermals, mask, grasping your
BCD in your teeth, your fins balanced on your head and a tank
between your knees?

No? Me neither.

OK do it in shifts then. <sulk>

nigelH

"Nigel Hewitt" <nigelh@REMOVETHISnigelhewitt.net> wrote in message
news:bvhcjd$6b6$1@titan.btinternet.com...
> Hywel & Ros wrote:
> > Minor pedantic point, speaking as a novice diver, but has-been
> > (not-very-good) mathematician:
> >
> >> Now go home. Wait until everybody is out. Put the full, yes
> >> I said full, kit back on. Stand on the bathroom scales.
> >> Weight in Kilos please.
> >
> > It's slightly easier to merely carry your gear onto the scales.
> > No real need to actually wear it in the house after all
> > And you can even weight it in batches and add the numbers up.
>
> But that's no fun to write. Anyhow have you ever tried to stand on
> the scales clutching your dry suit, thermals, mask, grasping your
> BCD in your teeth, your fins balanced on your head and a tank
> between your knees?
>
> No? Me neither.
>
> OK do it in shifts then. <sulk>
>
> nigelH
>
>

More fun... stick the bathroom sclaes in the back of the car and tkae them
along to the dive site...

Ok, you may get a few funny looks at the site but so what, it's not like a
lot of them couldn't do with a weight watchers subscription! ;)

rhys