Add extra weight for air in tank?

[DivemasterDennis]

Proper weighting is critical to enjoying a dive and has a huge impact on buoyancy and body control. There are two times weighting is crucial. The first is at the outset of the dive. You need proper weighting to descend. The second, and most critical point, is at the end of a dive. You need adequate weighting to control your ascent and to hover without exertion for a safety sop at 15-20 feet at the end of the dive. That is the practical formula. If you can't hold a relaxed hover at the end of the dive, add weight for the next dive in the same equipment and conditions. One reason I am a nut about logging dives is that the long becomes a data base for the diver concerning, among other things, proper weighting when using specified gear in specified conditions. Divers get lazy about weight checks, and so do dive concessionaires ( though liveaboards invariable have a weight check moment that everyone should have). That's why a log book of data is so useful. For my wife and I, assuming no great fluctuation in our personal weight, I can reference our last dive in the same gear and conditions and note the proper weight.
One last comment, and I know some will disagree with me, BUT... for Recreational diving, it is better to be a little bit overweighted than to be underweighted.
DivemasterDennis

 

[DevonDiver]

One last comment, and I know some will disagree with me, BUT... for Recreational diving, it is better to be a little bit overweighted than to be underweighted.

I don't disagree with you, but... that statement is (ab)used by many dive professionals as an excuse for not establishing proper weighting techniques as a skill in entry-level (and higher) divers.

Of course, proper weighting can only be confirmed with an empty tank - so that leads most divers (in unfamiliar kit) to conducting their first dive using a 'guestimation' approach. In that solitary instance, it's better to err on the heavier side and reduce weight as part of the weight check. Very few divers are going to obtain a nearly empty tank and run into the sea prior to diving, just to check their weighting.

However, far too many divers also emerge from training with no real conception of how to conduct an effective weight check.... or even the possessing an understanding that their diving would significantly benefit from such a check even being conducted.

Overweighted is better than underweighted. Neither state should be a deliberate alternative for being properly weighted.

 

[FPDocMatt]

Thank-you, everyone, for the thoughtful advice.

I've only done a few dives, and had at least 1200 psi left at the end of each of them, so I want to get this right before I do a dive in which I have 800 psi at the 15-ft stop. Even with 1200 psi with an empty BCD I had a bit of trouble staying at 15 ft (needed to hold the line). So I do indeed need more weight (with that equipment set-up). Perhaps increasing from 16 lb to 18 lb is not enough. 5# would be 21# (or 20# or 22# to keep an even number).

 

[dmoore19]

Thank-you, everyone, for the thoughtful advice.

I've only done a few dives, and had at least 1200 psi left at the end of each of them, so I want to get this right before I do a dive in which I have 800 psi at the 15-ft stop. Even with 1200 psi with an empty BCD I had a bit of trouble staying at 15 ft (needed to hold the line). So I do indeed need more weight (with that equipment set-up). Perhaps increasing from 16 lb to 18 lb is not enough. 5# would be 21# (or 20# or 22# to keep an even number).

They use S72 cu ft tanks at Sunset House. My experience has been that most places have AL 80. This will change how much lead you need.

 

[Thalassamania]

One of the things that you should keep in mind is the old saw, "a pint's a pound." What that tells you is that if you shift the midpoint of your breathing cycle by a pint you also shift your buoyancy by a pound. The more you dive the more comfortable you will get with this technique.

I must second DD's comment about weighing, neither under, nor over weighting are acceptable ... weighting can be off by a few pounds if you are comfortable with this breathing technique, but it should be right on the money. Frankly I am appalled that one who presents as a "Pro" and an author would condone such sloppy procedures, but then perhaps I am just a buoyancy snob.

 

[herman]

You have it about right. A the beginning of the dive- full tank- you should find your neutral weighting with an empty BC and then add the amount you need to compensate for air use (5ish lbs for an 80). Your lungs should be 1/2 full when you are neutral, not completely full. The above and below half full is your fine/active buoyancy control. When you exhale to descend, this should start a delayed, slow and gradual decent, not a rapid and instant decent. Most divers are too impatient and think they should start descending instantly and quickly.
I do agree with Pete, it's much better to do the weight check at the end of the dive to eliminate any trapped air in your wetsuit and gear.
​

 

[spectrum]

Just to beat a dead horse, checking one's weighting is not a once in a lifetime event.

There is a place for a quick and dirty before the dive check that will let you make a dive, probably a few pounds over weighted to get to the end of a dive where you can get some real answers. You are infinitely safer being a few punds heavy than light.

Over time your needs will change as gear ages and gets changed. As you configure for different dives and dive in different waters. Your comfort and skill are bound to change. If you pay attention and do a good logging you can end up with several key configurations that you tweak as you interchange items.

It's good practice to challenge your weighting anytime you burn your tank down near 500PSI. It only takes a moment to see how it all behaves with an empty BC. Do you sink, float or hang at your chosen depth?

Pete

 

[gmanstan]

A point that you need to keep in mind as well is that you might start off a little heavy and drop weight a little at a time to achieve optimum buoyancy, but it might still change a little over time as 1) you get more comfortable, 2) as your suit compresses 3) sometimes our bodyfat% changes especially after the holidays you might get a little more buoyant.

 

[oly5050user]

Thank-you, everyone, for the thoughtful advice.

I've only done a few dives, and had at least 1200 psi left at the end of each of them, so I want to get this right before I do a dive in which I have 800 psi at the 15-ft stop. Even with 1200 psi with an empty BCD I had a bit of trouble staying at 15 ft (needed to hold the line). So I do indeed need more weight (with that equipment set-up). Perhaps increasing from 16 lb to 18 lb is not enough. 5# would be 21# (or 20# or 22# to keep an even number).

the more you dive you will find you will need less weight..That said if you are using 18 lbs and in a 3mm wetsuit you are probably way too heavy unless you are a 6'4" person that weighs close to 300lbs..really should work on it.Use calm relaxed breathing cycle,stop moving hands/feet while hovering, lean to you right in a vertical with left shoulder higher than your right shoulder to get ALL the air out of your bcd...I recently had a customer come back from a trip that I did a refresher for at the lds a few months ago.He thanked me profusely in front of a bunch of customers on the way I showed him to reduce amount of lead he was using.He started out with 22lbs in a 3mm suit in salt water and now is using 8lbs in salt water with same 3mm suit. He is not a small person .Even the Dm he dove with on vacation argued with him that he would need more lead,until he proved them wrong...

 

[beaverdivers]

I think all the above info covers it. Just make sure not to use your air as weight!