Neutral Buoyancy

[landlocked]

Buoyancy still confuses me. This is ok because I am a new diver. What I have learned is.... I should so weight myself so that, (on the surface in a vertical position with my BC totally deflated, single tank newbie stuff) when I inhale the water should split my mask and when I exhale I should begin to decend. My question is then, what happens if I am diving shallow, 20-30 feet and the tank gets a little empty? The cataloge I am reading says that there is aproximately 6 lbs difference in buoyancy between a full and an empty aluminum 80 tank. Won't that much difference make it hard to stay down?

 

[jetblast00]

the proper amount of weight for you is just enough to keep you neutral at 10ft (while horizontal is better here) with a minimal amount of air in your tank (300-500psi, what you would end a dive with) and no air in the BC.

 

[Uncle Pug]

Originally posted by landlocked
Won't that much difference make it hard to stay down?

Folks diving the AL80 often find themselves a little light in the rump when the tank gets down there to the red....

So the solution is generally to add extra weight to accomodate that and the tendency is to add too much....

Jet's suggestion is a good starting point and as you gain experience you will be able to refine it....

You will find that after some time diving and getting comfortable in the water your breathing pattern will change and you will be able to reduce the amount of extra weight you carry.

 

[Ontario Diver]

If you do your boyancy check with an AL80, and your tank is full, add another 5-6 lbs to negate the bouyancy that an empty tank occurs. And if in doubt, err on the side of being heavy. Better to get a little tired and not be as streamlined than trying to hold yourself down towards the end of a dive or at the safety stop.

Also try doing your bouyancy check at the beginning and end of your dive.

You should find that as you get more comfortable, you'll be able to reduce the weight that you need to carry.

 

[GP]

I remember in my open water training I had the problem of not being able to stay down with an AL 80 that was getting low on air once I got up to just above 15ft. Adding a little weight like Uncle Pug and Ontario Diver suggested will do the trick for you. I've since been renting Steel tanks and haven't had to deal with it but I may end up buying AL tanks since they are half the cost of steels. It sure is nice not having to add that extra weight with steel tanks though.

 

[Drew Sailbum]

Any tank - aluminum 80 or steel 105 - will be more buoyant at the end of the dive when the tank is nearly empty. If you are doing your buoyancy check with a full tank, you will need to add a few pounds to compensate so you can comfortably do your safety stop.

 

[ScubyDoo]

According to the "Peak Performance Buoyancy" chapter in PADI's Adventures in Diving, you should estimate your weight requirements and perform your buoyancy check. Once you have optimized your weight so you float at eye level while holding a normal breath, and sink slowly upon releasing that breath, then you add extra weight to allow for an emptying cylinder in the later part of your dive. An AL80 generally requires an additional 5lbs of weight. Most people would prefer not to waste the time getting thier buoyancy right and then add 5lbs, so a lot of people just go ahead and calculate estimated weight required and add the 5lbs for the tank on the front end. As long as your exposure protection and gear configuration stays the same, you should not have to change your weight settings unless you move from fresh water to salt water or visaversa. If you move to salt water you will need to add additional pounds, and remove weights if moving from salt to fresh water.

They supposedly have "neutral bouyancy" tanks out nowadays which are supposed to be neutrally buoyant when empty? I havent heard much comment from the board about these tanks, so I dont know how well they perform?

 

[landlocked]

Thanks one and all for the information. It is nice to have such a great and readily available resource.

 

[scubabunny]

The NB aluminum 80 tanks are AWESOME!!! I don't think anyone else uses them but us (Guam). I HATE diving with Standard 80 aluminum. Even if I put extra weight on (for Yap and Bali) I'm still fighting the tank.

Neutral bouyant tanks are just that at 500psi. I think they are .5 positive when completely empty. But they make bouyancy so much easier...I still don't understand why more people don't use them.

 

[cougar]

Before my first OW dive I had read, heard and studied about bouyancy control...but it was all theoretical. First dive I just obeyed my instructor, but there was all this coral and I was so concious that one clumsy fin could destroy 200 years growth of coral...I was paranoid and not very comfortable with bouyancy. On our 2nd dive my daughter's problem became my good fortune as far as learning

Tina started to ascend inadvertantly, panicked, didn't flare and all of a sudden she was flying for the surface. Our instructor signalled to ask me if I was alright...gave me a "sit, stay" signal and hurried to help Tina. (He already knew us well enough to be pretty sure panic was not my style and that I was really comfortable in water) I settled down on my knees on the sand at 35 ft. for a moment. I looked up...no Tina, no instructor. Oh my god!! WHere's Tina, is she OK? EEk I'm all alone 35 ft underwater!! 10 secs of stomach churning then...Yeah, I checked my pressure guage, I've got plenty of air...I'm not being eaten by a shark, no worries, mate. So I relaxed...then I got bored...just sand....nothing pretty to look at...I wasn't s'posed to wander off. What was it Carlos said about controlling your bouyancy with your breathing? (Yes, I know I should have been more worried about Tina, but our instructor was terrific and I knew he could take care of her better than I could) I took a slow deep breath and stayed relaxed...wow! I went from my kneeling position to hovering at a 45 degree angle with my fins touching the sand and the rest of me just hanging...I breathed out and was laying almost flat on the sand...hey...this is cool. I continued to play until I could hover any place I decided on. I set goals for myself, hover horizontal one arms length from the bottom...two, three...then lay flat on the bottom. By the time Tina and our instructor returned I could hold position almost anywhere. (Tina decided that night she was incompetent and would never dive again...we talked 'til three in the moning...she went out the next day, solved her problem and all is well now. Good thing since she's heading for a speciallty in marine mammals at vet school)
I believe that time of playing and figuring out how the breathing worked was invaluable for me. Three days later we were swimming thru small arches of coral by looking at the size of the hole, positioning with breathing and sliding right thru the center touching nothing.

I've since gotten Tina to play a little bit on a nice safe sand bottom ...I think taking the time to figure out what different breathing patterns do to your bouyancy can make a huge difference. Not only did my confidence soar....but on a later dive when the DM handed me smaller weights than I had been using and I realized at the end of the dive that I was 4 lbs under my accustomed weight....I was still able to handle the boyancy (Only problem was holding at the 15 ft safety stop on ascent...I did have to fight to stay there) Other than that I never even noticed I was light...I checked the weights when I got on the boat 'cause I wondered why holding at 15 ft had been so difficult. So...ask your instructor if you can have some bottom time to play with breathing patterns...it sure worked for me.