Doubles, Weight and Dry

[LavaSurfer]

I wasn't quite sure where to put this
In diving doubles how would I calculate my weight

Steel 130’s weigh -10.5 lbs full and -1.0 empty each
The Manifold and Regs probably another 3.0 lbs (need to get this spec)
SS Backplate - 6.0 lbs
Total full system -29.0 lbs Full and -11.0 Empty

AL80 -2.0 full and +4.0 empty

Here is the question
Diving Dry this weekend I used 16 lbs lead (6 lb Backplate and 10 in pockets) and was probably 2 lbs heavy at the end where my al80 was close to +2.0 buoyancy
That means I would need 12 lbs to get down with no tank, right?

Next question, if it takes 12 lbs to sink me and my suit and the double streel 130's weigh -29.0 I am good with no weight? That's sort of a duh.
Then next if every 362 lbs in the tank is equal to -1.0 lbs bouyancy then hypathetically speaking, if I came up with 362 lbs in the tank (Maybe I got tangled) I have
-9.0 for the regs, manifild and backplate
-2.0 for the tanks empty
-2.0 for the 27 CF of Air
-13.0 buoyancy at the surface.

Does this sound right?If so then I stay with the SS backplate and no ditchable weight.
Am I way off or am I close?

Thanks

 

[DeepSeaExplorer]

I'm home sick with a headache, so I'm not going to follow your math. I will say you don't need any weight with 130s, and you will probably find the SS plate too heavy. I use an AL plate with PST 104s.

 

[LavaSurfer]

I'm home sick with a headache, so I'm not going to follow your math. I will say you don't need any weight with 130s, and you will probably find the SS plate too heavy. I use an AL plate with PST 104s.

Sorry, I know, it made me dizzy and now I have a headache.
I later found a thread and it validated my thinking.
Best just put it on and try it out.

 

[nereas]

I wasn't quite sure where to put this
In diving doubles how would I calculate my weight

Steel 130’s weigh -10.5 lbs full and -1.0 empty each
The Manifold and Regs probably another 3.0 lbs (need to get this spec)
SS Backplate - 6.0 lbs
Total full system -29.0 lbs Full and -11.0 Empty

AL80 -2.0 full and +4.0 empty

Here is the question
Diving Dry this weekend I used 16 lbs lead (6 lb Backplate and 10 in pockets) and was probably 2 lbs heavy at the end where my al80 was close to +2.0 buoyancy
That means I would need 12 lbs to get down with no tank, right?

Next question, if it takes 12 lbs to sink me and my suit and the double streel 130's weigh -29.0 I am good with no weight? That's sort of a duh.
Then next if every 362 lbs in the tank is equal to -1.0 lbs bouyancy then hypathetically speaking, if I came up with 362 lbs in the tank (Maybe I got tangled) I have
-9.0 for the regs, manifild and backplate
-2.0 for the tanks empty
-2.0 for the 27 CF of Air
-13.0 buoyancy at the surface.

Does this sound right?If so then I stay with the SS backplate and no ditchable weight.
Am I way off or am I close?

Thanks

With my twin 130s and a 6 lb SS backplate, I use 14 lbs of hard weights on my belt, for perfect buoyancy.

So you sound fine to me.

Breathing mix weighs about 0.08 lbs per cu ft, and that is what you need to compensate for, with a weight belt. Normally you always would want your weight belt to equal the displacement of your breathing mix (0.08 lbs / cu ft x volume of compressed cu ft).

You can try breathing down your tanks to about 250 psi, at the end of your dive, and verify that with an empty wing at 15 fsw you are completely neutrally buoyant. That is the ultimate test.

Everyone is different, and different thermals will give different results as well. New, thick thermals will require more weight than old, thin ones.

 

[nereas]

... I will say you don't need any weight with 130s, and you will probably find the SS plate too heavy. I use an AL plate with PST 104s.

Everyone is different.

You should always be able to create neutral buoyancy at any stage of a dive. The weight belt should equal the volume of the breathing mix times 0.08 lbs per cu ft.

For twin 130s and steel tanks, this comes to about 10 to 14 lbs, if you do the math.

 

[LavaSurfer]

Everyone is different, and different thermals will give different results as well. New, thick thermals will require more weight than old, thin ones.

True that, I was only wearing a 200 fleece jacket and pants with some under armor this weekend. Got a bit Nipply at the bottom. Thermo read 39 degrees. Brrrrrrr.
When I wear the thick suit, I need 8-10 more in lead.

 

[micklock]

with my aluminum backplate and two hp 80s (-9 full -3 empty) I don't need any weights with my neoprene drysuit, hood and gloves.

 

[nereas]

with my aluminum backplate and two hp 80s (-9 full -3 empty) I don't need any weights with my neoprene drysuit, hood and gloves.

This is what I would call unsafe diving.

Essentially you have no ditchable weight, and therefore you have no way to establish neutral buoyancy during your dive.

 

[JeffG]

With my twin 130s and a 6 lb SS backplate, I use 14 lbs of hard weights on my belt, for perfect buoyancy.

LOL...for perfect overweighted buoyancy that is. With my 130's, Alum plate and tail weight of ~5 lbs, I need about 4-6 lbs belt for salt water.

That's using a drysuit with 400gm DUI underwear.

So that is putting you at ~7 lbs overweighted. (assuming salt water and same undergarments. But given that the 400gm thinsulate is probably the most buoyant stuff around...)

 

[JeffG]

This is what I would call unsafe diving.

Essentially you have no ditchable weight, and therefore you have no way to establish neutral buoyancy during your dive.

<snicker>

and by your weighting given above, your solution is to add more weight to your belt to "add" to the ditchable weight.

All you did was make yourself even more negative.

Thanks for the proof that you have no clue.