Add Additional Weight For Shallow Dive?

[snowdog61]

Ideally you want to have an empty BC and holding steady at your 15' stop with ~500psi. Having a lb or 2 extra isn't a big deal - being light (or way lite) and having to fin down to hold sucks (been there).

 

[nolatom]

Only dive where there are rocks.

Put a couple in your pocket on the bottom, when your know-it-all instructor isn't looking.
then you'll be heavy enough at 15 feet, and instructor will feel self-satisfied, and move along to someone else.

;-)

 

[Storker]

Most people do not conduct a weight check with a tank that is around 500psi (50bar),

<nitpick>500 psi is around 35 bar, not 50 bar. There's roughly 15 psi to a bar.</nitpick>

<somewhat off topic>here in metric country, 50 bar reserve has been the standard rule of thumb for quite a while. As far as i know, the standard rec tank has gone from being a 15L 200bar to a 12L, either 232bar or 300 bar, or a 10L 300bar, while the reserve has stayed at 50 bar. Now, 50 bar in a 15L tank is the same amount of gas as 75 bar in a 10L tank. Considering that an Al80 is around 11L, 500 psi / 35 bar definitely is a smaller reserve than even 50 bar in a 10L tank.</sot>

 

[BRT]

I'm really not interested in a weight that is barely good at 500 psi. I want to be able to breathe that sucker down if I am in a tight situation very close to NDL's and I don't want to struggle to do it.

 

[Storker]

I have spoken to at least two instructors who said I use way too much weight

I've lost count of the number of people who, when hearing how much lead I'm carrying, have told me that I'm seriously overweighted. Nevertheless, if I'm down to - or below - 50 bar tank pressure during my safety stop (and don't carry a catch bag with a decent amount of scallops), I sport a classy waffle pattern on my skin when doffing my suit, from my wool mesh underwear. And it's always a relief to hit the suit inflate button when I'm topside, because I've been seriously shrink-wrapped for the last five to ten minutes of my dive.

 

[BRT]

And it is not ideal to be cold on a safety stop. Ideally when you quit swimming and start hanging you should put in more insulation not less.

 

[Storker]

Ideally when you quit swimming and start hanging you should put in more insulation not less.

...which indicates that the absolutely minimal weighting often pushed by some divers isn't necessarily a good idea, particularly if you're diving dry in cold water. As TSandM (at least) once said, air is loft and loft is warmth. I like to add a kg or two to my belt during winter.

 

[BRT]

Me too. I always agreed with Lynne on this.

 

[Bob DBF]

I'm really not interested in a weight that is barely good at 500 psi. I want to be able to breathe that sucker down if I am in a tight situation very close to NDL's and I don't want to struggle to do it.

500# in my 120 is 17 cuft or about 1.4# of buoyancy change to 0#. If I did my weight check right, I can easily control that buoyancy change with my lungs. If I didn't, a pound or two "extra" is more than enough. Just keeping the weight even on both sides of my weight belt will usually cover the issue.

The only issues with more weight than you need is you will have a larger bubble in your BC to expand and compensate for as you go shallow, and the tendency for an an AL tank to lift the bottom of the BC up and away from you if you are in horizontal trim, also increasing the bubble.

I must admit to a bias because of the way I was originally trained, I want to get to the surface and be slightly positively buoyant with my weight intact and some air in my tank.

Bob

 

[TMHeimer]

No, it is more.

The relative pressure change is what matters as that is what causes an equivalent change in the gas volume in your BC.

33' to the surface is a change of 2 ATA down to 1 ATA. 50% difference from 'depth'.

133' to 100' is a change of 5 ATA to 4 ATA, still 1 ATA difference, but now only 20% from 'depth'.

Yeah. I found that out in practice on my first couple of "deep" dives--even as a brand newbie you're fooling with the inflator much less down there. Perhaps your dive profile may determine if you want to add a pound or two over what your weight check said. If you're at basically the same depth most of the dive, a little extra BC air would be less of a hassle than if you were multi-level diving. Either way, I just use what the weight check says.