Buoyancy Issues

[boulderjohn]

Your buoyancy is a matter of your total volume and your total weight in comparison to the total volume and weight of the water you displace. If you are heavier than the volume of water you displace, you will sink. If you are lighter, you will rise. If you increase your volume, you rise. If you decrease it, you sink. The variable parts of your volume are your BCD wing, your wet suit, and your lung/chest volume.

Now for the joker. According to Boyle's Law, the volume of the BCD wing and the wet suit will change as you change depth. The closer you are to the surface, the more rapid the change. This will be very pronounced in a swimming pool. At our altitude in Colorado (yes, altitude makes a difference), a BCD will increase its volume 40% going from the bottom of an 11 foot pool to the top. A wet suit will make the same percentage change.

That means that if you rise a couple of feet in the water column at that depth, you will find yourself on the way to the surface. To overcome this, you will need to do something to arrest that ascent, and the easiest way is USUALLY to exhale to lower lung/chest volume to compensate. This will usually work, unless you are overweighted. For every pound you are overweighted, you need to have 15 fluid ounces of volume in the BCD wing to compensate. Those 15 fluid ounces are reacting to the change in depth. If you have enough of that unnecessary volume, then your lung/chest volume cannot possibly compensate.

Reading the initial post, my immediate thought was "overweighted." Try taking some weight off and see what happens.

 

[gfaith]

@PunkabillyTurk the weight you stated is that in salt or fresh water? You probably have a 5-7 lb change from salt (more lead) fresh (less lead) assuming you are using the same kit in both.

 

[Streydog]

I thought I was a hopeless air hog not too long ago but now I know I was over weighted. Keep diving and keep taking the weight off. I am using 8 lbs less now than when I started 3 years ago and it has made a dramatic difference. Diving just keeps getting more and more enjoyable for me. There is truth to the advise given of just keep logging dives. I can't wait to see how I will feel after the next 100 dives.

 

[TMHeimer]

I often read on SB about those dropping all kinds of weight when becoming more experienced. Over the 10 year period of my first used wetsuit I did drop about 6 pounds. But had to put it back on with the "new" used suit 2 years ago. So, I guess in 12 years I really dropped no weight. I did a weight check early on and basically my amount of weight didn't change unless for the obvious such as Steel vs. AL tanks I owned--and as mentioned, the old wetsuit's loss of integrity. Does that mean I was either great with my diving to begin with or that whether I was great or sucked back then and sucked more because I was unable to drop any weight with more experience? I always figured a weight check is a weight check, whether you have 1 or 1,000 dives. Trim and good buoyancy is another thing of course. Some instructors at the shop have agreed with me. Am I wrong?

 

[KevinNM]

I've seen OW students doing a weight check while finning continuously. They are nervous, it happens. I suspect that once they relax they will lose some lead with the next weight check.

 

[ScubaWithTurk]

Lots of great suggestions here that I will work on putting into practice this weekend. I am thinking of doing a buoyancy check on dive one and then do a post dive check with my near empty AL80 to adjust weight as needed for dives two and three.

As far as breathing is concerned, I am a practicing Buddhist and a meditation instructor on top of doing Yoga. I thought I would have this breathing thing down pat. But I realized that when I meditate I breathe in through my nose and exhale out my mouth which doesn't work for scuba. So back to the drawing board with that one.

 

[Streydog]

I often read on SB about those dropping all kinds of weight when becoming more experienced. Over the 10 year period of my first used wetsuit I did drop about 6 pounds. But had to put it back on with the "new" used suit 2 years ago. So, I guess in 12 years I really dropped no weight. I did a weight check early on and basically my amount of weight didn't change unless for the obvious such as Steel vs. AL tanks I owned--and as mentioned, the old wetsuit's loss of integrity. Does that mean I was either great with my diving to begin with or that whether I was great or sucked back then and sucked more because I was unable to drop any weight with more experience? I always figured a weight check is a weight check, whether you have 1 or 1,000 dives. Trim and good buoyancy is another thing of course. Some instructors at the shop have agreed with me. Am I wrong?

Your are right, a weight check is a weight check. Looking back I just don't think I ever did a weight check properly. I always relied too much on my BCD throughout the dive and would fin, didn't seem like much but probably was, during my safety stop.

 

[george_austin]

Just a ton of diving and working on your breathing will get you where you want to be. Where is that? Eventually you'll be able to accurately tell yourself, or anyone else, how much air is in your tank by the buoyancy swing - that's when you're in the zone and you're ready to do any dive with no BC - assuming you're diving wet with a steel tank. ( Aluminum is for resort diving and such ) You can still do the same exercise with AL tanks, I suppose but I only use those when traveling on dive trips. Great thread

 

[Dizzi Lizzi]

Lots of great suggestions here that I will work on putting into practice this weekend. I am thinking of doing a buoyancy check on dive one and then do a post dive check with my near empty AL80 to adjust weight as needed for dives two and three.

As far as breathing is concerned, I am a practicing Buddhist and a meditation instructor on top of doing Yoga. I thought I would have this breathing thing down pat. But I realized that when I meditate I breathe in through my nose and exhale out my mouth which doesn't work for scuba. So back to the drawing board with that one.

LOL!!!

 

[rongoodman]

That means that if you rise a couple of feet in the water column at that depth, you will find yourself on the way to the surface. To overcome this, you will need to do something to arrest that ascent, and the easiest way is USUALLY to exhale to lower lung/chest volume to compensate. This will usually work, unless you are overweighted. For every pound you are overweighted, you need to have 15 fluid ounces of volume in the BCD wing to compensate. Those 15 fluid ounces are reacting to the change in depth. If you have enough of that unnecessary volume, then your lung/chest volume cannot possibly compensate.

I would call that the second easiest way. The easiest would be with a couple of kicks. That's assuming you're flat enough in the water to start with, so you can go a little head down while doing so.