How much lead to use ...

SeaHound · Aug 2, 2009

I did my first sweet water dive a few days ago and it left me with weighing questions.

I was diving in a 3/2mm shorty with AL-80 tank with a rec wing BCD. With 6 lbs of lead I was ok in the beginning but felt light at the end of the dive. Had problems staying submerged. On the next dive, I added two more pounds (total 8 pounds) and was negatively buoyant until I blasted my wing almost full of air to acheive neutral buoyancy.

Can any one please help me with what I am doing wrong? 6lbs seems light at the end of the dive when the AL-80 is empty and 8lbs makes me sink!

lowviz · Aug 2, 2009

"A pint is a pound, the world around." Or a liquid pint's volume in gas gives you a pound of lift. Your sparse public profile (gear) makes it hard to give you the answer that you request.

elan · Aug 2, 2009

There is no much tricks you can get here. Just do a proper weight check as it's described in the OW manual. have 500 psi in the tank and you should be able to sink exhaling with your BCD empty and surfacing inhaling. Or you can do the check with full tank and then add 5lb with to your belt. Ask your buddy to check that there is no trapped air in your BC. IF your hose is attached to the harness or straps remove attachments. They do not let performing venting fully. You can also use the top or bottom dump valve depending on your BCD and position you use take in the water. Every time you change gear configuration you need to redo the check, unless you know how each particular item affects the buoyancy

boulderjohn · Aug 2, 2009

You are right in identifying the mystery--that amount of weight change should not produce such a drastic difference. There were therefore likely other factors at work, but there is no way to tell for sure right now.

My first guess would be that you had an air bubble trapped somewhere in your BCD on the first dive and not on the second. That happens a lot.

If I were you, I would go back to the lighter weight on a subsequent dive and then really check carefully for trapped air if you feel light at the end of the dive. Remember that air always wants to go up, so look for some part of your wing that is higher than the rest. You may want to roll around to force air to move to a dump valve to get rid of it.

BLUESEASONBALI · Aug 3, 2009

do a peak performance buoyancy course!!

spectrum · Aug 3, 2009

What is sweet water?

I agree that something else must be happening. A 2 pound change should not be significant if diving with a BC.

Pete

SeaHound · Aug 3, 2009

Sweet water = fresh water. Yes I think there was a trapped air bubble somewhere. I will give it a try once again. Thanks ...

Dr Neil · Aug 3, 2009

Next time I'm in a cold-green quarry, I'll remember that the water is really sweet!

Did you dive both dives with the same type of tank?
Did you add water to your BC bladder by depressing the inflator button while it was above your head?

vel525 · Aug 3, 2009

Not sure how new to diving you are, but I've seen that many new divers unconsiously kick or use their hands. Maybe on one of the dives you were doing something like that?

I agree with the previous replies that 2lbs shouldn't be giving you such a drastic change.

elan · Aug 3, 2009

SeaHound:
Sweet water = fresh water. Yes I think there was a trapped air bubble somewhere. I will give it a try once again. Thanks ...

if you find it sweet

check for a chemical plants nearby

How much lead to use ...

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