End of Dive Buoyancy Control

[DNK]

Okay,
Here is the deal:
I'm 5' 11" about 220 and fairly dense and with a large lung volume.
From the formula's I should be wearing some where about 32lbs of lead for a dive.
10% of 220 + 6 for a 7mm wet suit + 4lbs for a al80 = 32lbs.
But with a full tank(al80) I only need 16 lbs to float at eye level with a normal breath, 20lbs with a full. With an al80 at 500psi I float at eye level with empty lungs and 16lbs, with 20lbs I float at eye level with a normal breath.

So I would think I should be okay with 20lbs of lead. Which I am until I come up at the end of a dive. Once I hit between 15 and 20 feet my bouancy goes to sh##t. My feet start floating, I have a hard time staying down, air gets caught in my BC ( I have to do gymnastics to get any of it out.)

My wet suit is new (<15 dives on it) and the BC is a Zeagle Brigade. I usually have 6lbs in each BC pocket and 4 in each back weight pocket.

I have tried using more lead (up to 30lbs total) under advice of buddies, but all that happens is that I am really heavy during the dive(BC is about 1/2 full at 70') which makes bouancy control throughout the dive a nightmare.
The funny thing is that even with 30 or 32lbs of lead I still have a hard time staying down at 15 to 20 feet.

I plan on burning a tank next week just playing with bouancy, but was wondering if anybody could help me with things to look out for or specifically work on.

The best I can come up with is that once the wet suit decompresses I feel a sudden surge of bouancy and start breathing heavier because I'm worried about my bouancy.

Thanks

 

[Darin]

DNK,

Don't worry about all of the hype of what everyone "thinks" you should use based only on your body size and shape. I'm a couple of inches shorter and a few pounds lighter than you. Everyone TOLD me that I'd need 20+ pounds in the ocean in a full 3mm. After a buoyancy check, the instructor asked me how much weight I had, I said 8lbs. He said "That's a good weight for you". So, you see, everyone is different. The recommendation charts are just that, recommendations. Go with what works for you.

It appears you have done a proper buoyancy check and know what you need.

To work on your buoyancy, the Padi Peak Performance Buoyancy course is great. Other than that, if your dive center has a pool, go use that. When I was learning, my LDS let me come in and use their pool to work on my skills and such.

Get your own gear if you haven't already.(I know you listed gear) At the very least, use the same setup every time you dive if you are renting (unless you want to try different kinds of gear).

Biggest buoyancy challenge for most divers? RELAX! Ankle weights may help for the floaty feet.

If the problem is at 15-20 feet, then spend some time there and work on it. Use a line but don't hold on to it tightly, just use it as a reference.

After your weight is correct (as determined by the buoyancy check), the rest is breath control and the amount of air you put in or let out of the BCD. Remember, small puffs in and out.

My BC will sometimes trap a bit of air also. Experience will teach you how to get all the air our of it.

Well, I hope my ramblings will help. If you have other questions, PM me.

Darin

 

[cummings66]

Okay,
So I would think I should be okay with 20lbs of lead. Which I am until I come up at the end of a dive. Once I hit between 15 and 20 feet my bouancy goes to sh##t. My feet start floating, I have a hard time staying down, air gets caught in my BC ( I have to do gymnastics to get any of it out.)

One thing is certain, you're not taking into account the empty tank if you get yourself setup for a full tank and then don't add any weight with an AL80.

What you should do is get 500PSI in it and then check it out. Are you stressed or nervous at the end of a dive, looking forwards to getting out of the water? I'm wondering about the air in the BC bit, how much do you have in there at that depth? You are releasing it as you ascend I suspect, but I wonder if you're letting enough out?

 

[spectrum]

The formula will give only the grossest guess at what you need. As you note bone structure, lean body mass, the amount of neoprene, it's gas content and compressability all vary with brand, model and age. That and dozens of other case to case varriables.

You do cite the bobbing test working with 16 pounds and being in Heshey PA (had a neat family camping trip between there and Lancaster in 96) I'm assuming fresh water. That weight in fresh water with that tank sounds very light. Is it possible that you were inadvertendly finning during the test? Another thing would be that the full tank suggest you just got in the water. Another advantage to doing the check at the end of the dive is that stow away bouyancy has had a chance to escape.

For the moment lets assume the 16 pound starting point. You do need to add weight to compensate for anticipated air useage to 500 PSI.
AL-80 = 3000 PSI / 77.4PF = 38.75 PSI/CF
3000 - 500 = 2500 PSI to be used
2500 X 38.75 = 64.5 CF planned usage
Air = .08 LB/CF at 1 ATM
64.5 X .08 = 5.16 pounds must be added to the 16 pound result so call it 6 + 16 = 22 pounds. That completes the test you did but I suspect it may be tainted by entrapped air, dry gear and finning.

If you have any trepidation about surfacing which it sounds like you do now even if you didn't before then what you mention about pumping up your lungs could be happening.

You want thngs to try? Let's say your trim is such that you are prone or slightly feet up anyhow... As you aproach 10-15 your suit becomes more bouyant and the air in your BC bladder increases in volume. How are you venting ? Could you be getting slightly bottoms up and holding a bubble in the bottom of the BC? Are you using the bottom dump or only the inflator? Also consider moving the trim weight down into the integrated pockets or even moving some to a belt. You may be chest heavy more than foot light.

When I started my feet drooped when I stopped finning, I moved weight upwards on my system and trimmed out nicely.

Pete

Okay,
Here is the deal:
I'm 5' 11" about 220 and fairly dense and with a large lung volume.
From the formula's I should be wearing some where about 32lbs of lead for a dive.
10% of 220 + 6 for a 7mm wet suit + 4lbs for a al80 = 32lbs.
But with a full tank(al80) I only need 16 lbs to float at eye level with a normal breath, 20lbs with a full. With an al80 at 500psi I float at eye level with empty lungs and 16lbs, with 20lbs I float at eye level with a normal breath.

So I would think I should be okay with 20lbs of lead. Which I am until I come up at the end of a dive. Once I hit between 15 and 20 feet my bouancy goes to sh##t. My feet start floating, I have a hard time staying down, air gets caught in my BC ( I have to do gymnastics to get any of it out.)

My wet suit is new (<15 dives on it) and the BC is a Zeagle Brigade. I usually have 6lbs in each BC pocket and 4 in each back weight pocket.

I have tried using more lead (up to 30lbs total) under advice of buddies, but all that happens is that I am really heavy during the dive(BC is about 1/2 full at 70') which makes bouancy control throughout the dive a nightmare.
The funny thing is that even with 30 or 32lbs of lead I still have a hard time staying down at 15 to 20 feet.

I plan on burning a tank next week just playing with bouancy, but was wondering if anybody could help me with things to look out for or specifically work on.

The best I can come up with is that once the wet suit decompresses I feel a sudden surge of bouancy and start breathing heavier because I'm worried about my bouancy.

Thanks

 

[pasley]

let's do a little editing and get to the basic facts of your case:

Okay,
Here is the deal:
1... with a full tank(al80) I only need 16 lbs to float at eye level with a normal breath, 20lbs with a full.

2. With an al80 at 500psi I float at eye level with empty lungs and 16lbs, with 20lbs I float at eye level with a normal breath.

3. So I would think I should be okay with 20lbs of lead.

4. Which I am until I come up at the end of a dive. Once I hit between 15 and 20 feet my buoyancy goes to sh##t. My feet start floating, I have a hard time staying down, air gets caught in my BC ( I have to do gymnastics to get any of it out.)

5. The funny thing is that even with 30 or 32lbs of lead I still have a hard time staying down at 15 to 20 feet.

6 The best I can come up with is that once the wet suit decompresses I feel a sudden surge of buoyancy and start breathing heavier because I'm worried about my buoyancy.
...

Ok items 1 and 2 are the same numbers, something is not right there. You should need 4 pounds more of lead with an AL80 at 500 PSI. Or, once you get neutral, add 4 pounds for the shift of the AL80.

From your post is it clear that at 18 pounds of lead, 500 PSI in an AL80 tank, you float at eye level. So your buoyancy check is fine now add 4 pounds so you can stay at 15 feet. If you find you can hold 15 feet without it, drop it.

The inability to hold depth with 32 pounds of lead would indicate the challenge is not in your weight, but in your operation of the BC. You are waiting too late to vent your BC and the air and suit expansion is getting ahead of you . I agree with the others, you don’t need more lead, just more training and practice. Also concentrate on NOT moving your hands or feet and unintentionally swimming up.

Here is another rule of thumb to get you into the lead ball park.
7mm wet suit 2-3 pound (3 for new) of lead for each pound of wet suit, plus some lead for the Twinkies and other junk foods, plus 4 pounds for the AL80.

3mm wet suits would be 1-2 pounds of lead.
http://www.scubadiving.com/training/specialty_and_advanced/perfect_buoyancy_on_every_dive/

 

[scubafool]

I would try moving some of the weight to a weightbelt, maybe that will heop with the floating feet problem.

If you can get in a really shallow area, say 4-5 feet deep, at the beginning of the dive, try getting near the bottom and try various methods to dump all of the air out of your BC. I am not familiar with that BC, does it allow air to circulate from left to right if you are head down? You can check this, does the air cell go from side to side at the bottom & back of the BC? If it doesn't, even using the rear dump valve while head down will still leave air in one side, and cause the described problem.

Anyway, I would say to first fix the trim problem by moving the weight around until you get rid of the head down problem, then dial in your weight by doing bouyancy checks at 4-5 feet with a nearly empty tank, making sure that you can dump all of the air out of the BC. But remember, 1 extra pound won't kill your bouyancy, so kind of "grow down slowly" to your proper weight.

 

[Canadian_Diver]

With an al80 at 500psi I float at eye level with empty lungs and 16lbs, with 20lbs I float at eye level with a normal breath.

The two issues you are battling are compression of the wetsuit and an empty aluminum tank.

The best time to adjust and test for bouyancy is at your safety stop with about 500PSI of air in your aluminum, which sounds like this is what you're doing.

I would slowly start adding a pound of weight at a time (or 2 if you can't get 1lbs) until the symptom becomes manageable at the end of the dive.

One other factor is your breathing. I don't know what your breathing pattern, style, or such is. But I do know that it makes a huge difference. The best example of this I can think of is when I first started my pool sessions before being certified. At the beginning of the course, I needed 6lbs to submerge and stay down. Now, I need none.

Sounds like you're on the right track though.

 

[Canadian_Diver]

After your weight is correct (as determined by the buoyancy check), the rest is breath control and the amount of air you put in or let out of the BCD. Remember, small puffs in and out.

Hey Darin, I'm not sure if I understood your advise here or not.

The way that I read it, is that you're advising to take small short breaths. If this is the case, this is a very bad thing to do as it promotes the buildup of CO2 in the lungs, which in turn can cause anxiety or panic.

 

[jham2081]

Small puffs in and out of the BC, not your lungs

 

[Darin]

Small puffs in and out of the BC, not your lungs

Exactly....

Darin