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Mtrewyn
07-07-2008, 21:55
While I was diving this weekend, I thought I would try and cut back on the weight I was using.

I dropped a total of lbs and it was a little hard to get under but after I got under 10 feet sinking was not a problem I did not have a single issue the rest of the dive but... while at depth I had NO air in my BC, the only way I could change my depth with out swimming up or down, was to take a deep breath, or breath with shallow breaths, and I would go up and down accordingly.

My question is this, Is this a problem, not having air in the BC? or should I add some weight so I can add air in the bladder, or what do you all think?

Fireplug
07-07-2008, 22:16
Not clear in your post. How many pounds did you drop? Were you without any weight? My concern would be what happens at the end of the dive when you are trying to do a safety stop with a bouyant air bottle wanting to take you up. If you are that close....I think I would put 2-4 lbs. on.

I hate to try to get settled down on the sand for a picture op and can't "land" cause I'm light. Rather be a little heavy, but that's just me.

bubbletrubble
07-07-2008, 22:37
First off, it's great that you were trying to cut back on the lead you were carrying.

If you were having an issue with the initial descent, then your weighting may have been 6-8 lbs. off. During the dive, you are using up the air in your tank, so at the end of the dive you'll be more positively buoyant. An AL80 tank will gain almost 6 lbs. of positive buoyancy when the air is drained out of it. Higher capacity tanks will have an even larger buoyancy swing. For this reason, if you are optimally weighted for your dive, you should be negatively buoyant by the weight of your gas at the beginning of the dive. It should be rather easy to sink if you are 6lbs. negative, don't you think?

It is possible that there were air pockets in your wetsuit...and those air pockets were making you more positively buoyant than you would otherwise be. This is one good reason to do the weight check at the end of a dive.

When you do a proper weight check, make sure that you're doing it with a near empty tank. You can do this very easily at the end of a dive by purging your reg down to less than 500psi...and then doing the weight check.

You were OK on the descent past 10fsw because your exposure protection (a wetsuit, I'm assuming) was getting compressed by the greater ambient pressure...or the air pockets that I had previously mentioned were "disappearing."

There's nothing wrong with keeping no air in your BC. If you are trying to maintain a certain depth and you can do that without adding any air to your BC, it means that you are already buoyantly neutral. It really isn't a good idea to carry more lead just so that you have to offset that negative buoyancy by filling up your BC with air. You will work harder to move that extra weight through the water. Also, your filled BC will create more drag as you move. Both of these factors will make you work harder under water than you need to and increase your air consumption. Take the minimum amount of weight possible to carry out your dive, but make sure that you've figured out exactly how much weight that is.

Have fun and dive safe.

bubbletrubble
07-07-2008, 22:40
My concern would be what happens at the end of the dive when you are trying to do a safety stop with a bouyant air bottle wanting to take you up.

This is my concern, too. The OP should be doing a proper weight check at the end of the dive...or at least simulating end-of-dive conditions with a near empty tank.

mselizann
07-08-2008, 09:13
I always need to be a bit heavy for that reason- otherwise you just start ascending too quickly

Mtrewyn
07-08-2008, 19:36
I never thought of checking my weight at the end of the dive with an "empty" tank, I'll do that next time.

Just FYI I had 8lbs of weight on, 3mm wetsuit, and I dropped the 4lbs of other weight to see if I was using too much, but 4lbs is not all that much, so it might be worth it to put it back on

CompuDude
07-08-2008, 20:14
While I was diving this weekend, I thought I would try and cut back on the weight I was using.

I dropped a total of lbs and it was a little hard to get under but after I got under 10 feet sinking was not a problem I did not have a single issue the rest of the dive but... while at depth I had NO air in my BC, the only way I could change my depth with out swimming up or down, was to take a deep breath, or breath with shallow breaths, and I would go up and down accordingly.

My question is this, Is this a problem, not having air in the BC? or should I add some weight so I can add air in the bladder, or what do you all think?

You just described the ideal state of being for diving. Seriously.

The one caveat to that, is we need to be talking about the end of the dive, when you are at your lightest. If you're like this early on in the dive, as you continue to breath your tank down you will get lighter still, and having no air to dump, you will begin to ascend whether you want to or not.

Generally you will need some air in your BC to maintain depth earlier in the dive, and gradually you'll need less and less air in there as you reduce your weight (via breathing down your tank) throughout the course of the dive. Towards the very end of the dive, you should need almost no air in your BC. As long as you can stay put for your safety stop and make a safe ascent, with your tank practically empty, you're perfectly weighted.