Adjusting Weights

[Amadeus023]

Hello - I am a newly certified diver and I am trying to understand weights. I decided to purchase my own equipment because I don't like having to constantly have a new set of unknowns to work with each time I go diving. I am currently doing fresh water dives in lakes & quarries. I have done four dives on two occasions trying to checkout my equipment. I know that there are many factors that can impact the weight that you need. Anyway, I decided to hold off on my AOW certification until I could get a handle on my weights: Here is what I have used so far:

Dives 1-5: 13 lbs - 7mm wetsuit Quarry (OW Certification Dives)
Dives 6,7: 12lbs - 5 mm wetsuit Quarry (Equipment Checkout #1)
Dives 8,9: 19lbs - 0.5 mm wetsuit, Lake (Equipment Checkout #2)
5 mm wetsuit,
7 mm jacket

Well yesterday, I started out with some difficulty getting down with all that neoprene on. My divebuddy suggested that I use the buoy line to help me to descend and that I should be fine once I got below 3 ft. Okay, I did and he was correct. Everything seemed to be fine until we were 28 mins into my second dive and my air was at about 1000 psi. My dive buddy was leading and I was following. I realized that my dive buddy seemed to be getting further away from me and I thought that he must be going deeper. I tried to release any air that might be in my BCD so that I could follow and I realized that he was only getting further away from me. I decided to check my computer and I realized that I was ascending uncontrollably. I was very frightened because I did not know why this was happening. I decided to remain at the surface and wait for my dive buddy to ascend rather than try to descend and locate him because we only had about 5' visibilty.

Anyway, my dive buddy thought that I had done something to cause my ascent. I assured him that I did not do anything. I was troubled because this is very scary. I mentioned this to the guy when we turned in our tanks and he asked me how much air I had left. I told him that it was about 1000 psi and he said that it was my aluminum tank that caused it because they become bouyant at around 1000 psi. Talk about being scared! I learned yet another factor that can impact how we weight ourselves properly. I had no idea that I was getting an aluminum tank and that it would have this effect on my bouyancy.

I would like to know if there is any place that I can go and read about this subject rather than having to learn by trial & error. I am just thankful that we were only about 20ft deep. This would have been horrible if I had been diving deeper and then this occurred. I am trying to check things out with my gear prior to going to Roatan in November. I know that that will be a whole other set of circumstances because I will not have all these layers of neoprene to contend with. Please help me - TY!

 

[ScubaPrincess510]

hi mommy!!!!!! what's up????:lol:

 

[joe rock]

Hi Amadeus, I don't think any books are going to help you. There is a good article in this months Scuba Magazine on bouyancy and there are several articles on their website.

I dive mostly cold water in an 8/6 mil wetsuit (sometimes a 7 mil farmer john). When first certified a year ago I had all the problems you describe (it does get MUCH BETTER with experience). As you said in your post there are many factors impacting bouyancy. If you did a bouyancy check with a full AL80, you'll need to add 4 or 5 pounds to counter act it's bouyancy when empty. Best is to do a bouyancy check at the end of your dive when the tank is below 1000 psi. Log the weight and use that as your starting point on future dives. As you gain experience and comfort in the water, you'll begin to need less weight.

Another thing to keep in mind, with equipment changes it is very likely you'll impact the weight required. Also, you are going on a trip soon (lucky you). Diving in salt water will require you to add weight (using all the same gear including wetsuit!).

Good luck,

JR

 

[Charlie99]

If you did a bouyancy check with a full AL80, you'll need to add 4 or 5 pounds to counter act it's bouyancy when empty.

It's not the 4 pound buoyancy when empty that counts, it's the 6 pounds of air in the AL80 that counts. Whether your tank is steel, aluminum or kryptonite, as you use air it gets lighter and you gain buouyancy.

80 cubic feet of air (in any type of tank) weighs about 6 pounds. For a 3000psi AL80, that conveniently works out to about 1 pound for each 500psi. This means that you can adjust your weighting with any level of air in the tank, and then add in another pound of lead for every 500psi in the tank.

Amadeus, as you probably noted, the multiple layers of neoprene expand as you ascend and significantly add to your buoyancy. The same thing happens with any air that you have in your BCD. When diving with lots of neoprene, you have to stay ahead of things ----- once you start going up too fast, it's hard to stop the ascent.

Your lungs also change buoyancy quite a bit between fully exhaled and full inhaled. If you find yourself going up, in addition to dumping air from the BCD, you should also exhale as fully as possible.

 

[scubafool]

Well, there are a couple of things that could be causing you this problem.

You could be underweighted, your BC could have some trapped air that you did not manage to dump out, or perhaps a combination of the two.

The reason that you only experienced this as the tank got lower in pressure is that the compressed air in the tank has weight, and as you use up the air, the tank becomes more bouyant. Most aluminum tanks become positively bouyant (they want to float up to the surface), while most steel tanks stay slightly negative (they want to sink). So with an aluminum tank, you will need to wear more lead to compensate for the bouyancy than with a steel tank, if everything else is the same.

The first thing that you need to do is do a proper weight check. You could also rig up some lead weights with snaps ziptied to them, so that you can snap them off to various Drings on your BC. Leave these in shallow water where you can find them or have a shore bound buddy ready to hand them to you or whatever. Start your dive with the same weight as you did last time, or maybe a little more considering the issue you experienced, and head back to the shallow area when your tank gets down below 1000 PSI. Now obtain the clip weights. As your tank gets down around 500 PSI, try dumping all of the air in your BC and see just how many of the clip weights that you can hand off to your buddy before you start to ascend when you breathe in. Keep your breathing slow and deep. Ideally you should sink after the exhale and float upwards after the inhale.

Oh, one more thing. at the start of your first dive of the day, your wetsuit will have a lot of air trapped in it that it won't when it gets saturated, that's why you I reccomended doing the weight check at the end of the dive.

Once you have that worked out, get another tank and head back to the same shallow spot. Use the same amount of weight, with the same amount in clip weights. Now try moving the clip weights higher and lower until you are horizontal, or laying down in the water, when you are not swimming. This gives you an idea of how much weight to place where to get trimmed out. Options include a weight belt, trim pockets that come on your BC, an extra cam band that you can strap to your tank, etc.

 

[Bowtie22]

You could be underweighted, your BC could have some trapped air that you did not manage to dump out, or perhaps a combination of the two.

I would have to agree with this.... The other thing I will add to this is your breathing control..... Are you sure that you are taking deep breaths in and full breaths out....... Reguardless of that the main reason is either your BC was not fully deflated or you are underweighted. Make sure you do a proper boyancy check anytime you make changes in your gear configuration. After you find you neutral boyancy add about 2lbs to make yourself slightly more negative. Remember the fundamentals....... then get more experience diving and you will realize you can dive with less weight.

Good Luck!!!

 

[joe rock]

It's not the 4 pound buoyancy when empty that counts, it's the 6 pounds of air in the AL80 that counts. Whether your tank is steel, aluminum or kryptonite, as you use air it gets lighter and you gain buouyancy.

80 cubic feet of air (in any type of tank) weighs about 6 pounds. For a 3000psi AL80, that conveniently works out to about 1 pound for each 500psi. This means that you can adjust your weighting with any level of air in the tank, and then add in another pound of lead for every 500psi in the tank.

Charlie, you are correct, but as you know an AL 80 is positively bouyant when empty whereas steel tanks will be neutral or negatively bouyant.

JR

 

[spectrum]

Charlie, you are correct, but as you know an AL 80 is positively bouyant when empty whereas steel tanks will be neutral or negatively bouyant.

JR

That's true but irrelevant, The diver and all of his/her gear are taken as a whole. Any tank can be configured to dive in a stable manner. A diver with a steel tank may need less weight but if under weighted they will still go positive as they breathe the tank down.

I'm as muck of a steel fan as anyone but tank model/material not the root of the original poster problem. http://home.gwi.net/~spectrum/scuba_al80.html

A good weight check and assurance that he can/is really dumping all of his BC air is needed.

Pete

 

[Amadeus023]

Thank you for all of your help - you have given me lots of ideas to think about.

Pete - thank you for taking the time to put together those ScubaKnowtes! I read a few of the pages that you have done and they are wonderful for new divers. I will be sure to share this info to other new divers. I feel like I hit the jackpot today!

 

[donacheson]

It still amazes me how much difficulty divers, especially new divers, have with weights and buoyancy. The certifying agencies seem to be doing a poor job of training.