The art of Buoyancy Control

[Carribeandiver]

To be neutral is very important as it effects air consumption and the ability to relax and enjoy the sights instead of constantly checking the depth gauge.
Being a new diver, this is a problem for me. I read an article in Scuba Diving on proper weighting and tried the suggested technique.
That is, I weighted myself and jumped in, in full gear. If I managed to float at eye level on the surface, then my weight was correct.
I found the perfect weight amount and descended into the depths. Then the problems began, depth effects buoyancy. And as the tank empties, that too effects buoyancy. I found that I had perfect weight at the start of a dive but was underweighted at the end of the dive when my tank was positive (AL80).
What a struggle to do a free ascent and safety stop when you are positive. Up and down, up and down. 30 seconds at 20 feet, 30 seconds at 15 feet, 30 seconds at 12 feet, back to 30 seconds at 17 feet.
In short, it appears it is better to be overweighted then underweighted. Air can be added to a BC to compensate but what can you do if you are underweighted?
Any comments, tricks and/or tips would be appreciated.

 

[JeffG]

Being a new diver, this is a problem for me. I read an article in Scuba Diving on proper weighting and tried the suggested technique.
That is, I weighted myself and jumped in, in full gear. If I managed to float at eye level on the surface, then my weight was correct.

You were having problems because the mag is wrong. If you do that with an empty tank, then you are good. You need to add the weight of the air in your tank to your weight belt. ~1lb for every 13 cu ft. So for an Alum 80, add 6 lbs.

 

[jeckyll]

You were having problems because the mag is wrong. If you do that with an empty tank, then you are good. You need to add the weight of the air in your tank to your weight belt. ~1lb for every 13 cu ft. So for an Alum 80, add 6 lbs.

I can't believe I'm going to say this, but that's exactly how the PADI AOW book describes it (at least I think it was that one).

 

[fire_diver]

Like Jeff said, weight yourself for the END of the dive (tank nearly empty). Also, if you are making multi-level dives, then you will have to adjust your bouyancy repeatedly during the dive. They should be small adjustments though. Vent in small amounts as you ascend, short blasts of air into the BC as you descend.

If you could dive with no exposure protection, you don't need to much of anything. The thicker the wetsuit, the more adjustments you have to make. I started out in a 3/2. I had my bouyancy routines down great. Then I wanted to go deeper (colder) and got a 7mm. It felt like being a brand new diver all over again. It all just takes practice.

FD

 

[www.scubamazing.com]

Scuba Diving on proper weighting and tried the suggested technique.
That is, I weighted myself and jumped in, in full gear.

It can get somewhat confusing. Obviously there is a lot to take account for. I usually shore dive and so I'm constantly changing depths.

If you'll be renting wetsuits all the time, you'll have to get used to different buoyancy factors. I think zeroing on your weight with an empty tank is a good idea, but just realize you're still going to have adjust the air in you BC.

 

[Cacia]

and remember being in deco and not having enough weight is a big fat problem.

I scimped a bit the other day (just two pounds) and I thought "oh well...it is a deep dive, won't matter" No problems till my tank was empty, almost very empty and I had messed around too deep for too long.,...

Of course, you can usually swim downward but that 500 pounds you had a plan for will go quickly....

Suddenly, I am making many mistakes lately. At least I am seeing that.

 

[Walter]

Suddenly, I am making many mistakes lately. At least I am seeing that.

That's a phase many good divers go through. You are a good diver and you know it. You've made tons of dives, many of them where things went wrong and you compensated with no problem. You're so good you can get away with cutting corners. That attitude can kill you. Slap yourself silly and get over it. I shared my wake up call with you. Don't make yourself go through something similar.

 

[Cacia]

yea, I am trackin' on that, Walter.

thanks....You are so right. I have really messed up lately. Boat overload, I think.

You should start a thread on this subject, wise one. It is a very profound phenomena.

 

[herman]

................That is, I weighted myself and jumped in, in full gear. If I managed to float at eye level on the surface, then my weight was correct.
I found the perfect weight amount and descended into the depths. Then the problems began, depth effects buoyancy. And as the tank empties, that too effects buoyancy. I found that I had perfect weight at the start of a dive but was underweighted at the end of the dive when my tank was positive (AL80).
What a struggle to do a free ascent and safety stop when you are positive. Up and down, up and down. 30 seconds at 20 feet, 30 seconds at 15 feet, 30 seconds at 12 feet, back to 30 seconds at 17 feet.
In short, it appears it is better to be overweighted then underweighted. Air can be added to a BC to compensate but what can you do if you are underweighted?
Any comments, tricks and/or tips would be appreciated.

What you have discovered is you either have to do 1 of 2 things to get your weight dead on. Do your weight check at the END of the dive with your tank close to empty-500psi is somewhat the standard or do your weight check as you did but add enough weight to compensate for the weight of the air you will use, I find around 4lbs works for a 80cf tank. Note I said 80cf and NOT AL-80. The capacity of the tank is all that matters be it aluminum, steel or anything else. A 63cf would require less and a 100cf would require more. If you are properly weighted you start your dive slightly overweighted by the same amount as the weight of the air you intend to use. The dive is started with a little air in your BC to compensate for the extra weight. As the dive progresses and you use up the air in the tank, you will need to vent a little air from time to time to compensate for the used air.

 

[TSandM]

It is best to be correctly weighted, but you are right: Over is better than under.

If you find yourself significantly underweighted at the end of a dive, there aren't a lot of options. If there is something to hang onto, like an anchor or buoy line, you can use that to control your ascent. If you are in an area where there are rocks, you can pick up one or more (you'll be surprised at how little they help -- rocks aren't lead!) If the disparity is small, you may be able to stay down by pitching a little head down and continuously kicking down -- It's a PITA, but I've done it. If you have an overweighted buddy, he can get negative and hang onto you, but a correctly weighted person at the end of a dive isn't likely to be able to get negative enough to be much help.

The best strategy is to get your weight right to begin with. Neutral at the surface at the beginning of the dive, then add the swing weight (gas to be used), or weight check at the end of the dive with 500 psi in the tank.

For dry suit people, a friend made the observation the other day that, if you finish the dive, stand up in shallow water and bleed the tank to 500 psi, you are going to end up squeezing a lot more air out of the drysuit than you will ever manage while actually diving (because of the pressure differential between your underwater body and the out-of-water exhaust valve) and your weight check may result in you being a little light at the end of an actual dive.