Buoyancy Issues

[billt4sf]

The more weight you carry, the harder it is.

If you sink fast when you deflate your BC at the surface, you are probably overweighted. Ideally, you should sink slowly at first, with no air in the BC, no kicking when you exhale. You might want to try inhaling (to rise up just a tad in the water column) before you exhale and deflate. NO KICKING.

It takes time. Good for you for trying at the pool! You might want to work with an instructor, if you can find a good one.

- Bill

 

[stuartv]

Could be my weighting

...

I wear a 7 mil wet suit, 5 mil gloves (which I hate and have little to no dexterity in but that is another thread), Deep 6 fins, weigh 189 lbs and currently have 26 pounds of weight. 18 lbs in my BCD integrated weight pockets with 4 pounds each in my trim pockets.

Yes, you could be overweighted and that would make controlling your buoyancy harder. You didn't say, but I am assuming your above description was based on using an AL80 for your tank. 26 # sounds on the high side, to me, for only being 189 pounds - unless you are in "shape", where "round" is a shape. If it is with a steel tank, then it is even more likely that you are overweighted (in my opinion).

Regardless, the first step is to make sure you are not overweighted. The most sure way to do that is if you can get hold of a tank that is almost empty and use that to experiment in the pool. Some people will say that you only need to be able to get neutral at your safety stop, with an empty BCD and an almost empty tank. If you do that in a 7mm, then at the surface your suit will have uncompressed some and you'll be a little positive, even with an empty BCD and near-empty tank. Personally, I like to be able to descend without struggling, even when my tank is near empty. So, I aim to have an extra 1 or maybe 2 pounds or so, so that I can descend from the surface with an empty BCD and near-empty tank just by exhaling all the way. Either way, the difference in weight is small, so it's really up to your preference at that point.

Make sure your weighting is right before you worry about anything else.

Oh, and when you go to check your weighting, I would suggest to get in the pool in just your wetsuit first, get under the water, orient yourself head up/feet down, and pull the neck of your suit open at the front and back to let water in and make sure all the air inside the suit is pushed out. It can make quite a difference in your buoyancy just from the air trapped in your suit when you first put it on and get in the water. My first dive after finishing OW was in Mexico. I was having trouble getting down. The DM swam over, grabbed my suit at the back of the neck opening and pulled it out from my body for a couple of seconds. I got down just fine after that.

 

[J_Rod]

My question for the physics people, would be, Is lift relative? In other words, will an amount of gas needed to offset negative buoyancy, expand to provide the same relative amount of lift compared to a smaller amount of gas with a less negative mass? That is to ask, If I am VERY negative, and fill my BCD to be neutral, is that gas going to expand and create the same lift as compared to being slightly negative needing less gas in my BCD, or will more gas expand and provide more lift, thus causing buoyancy to be affected more over a smaller ascent (say, 5 feet, which is common in people having buoyancy issues). Is this simply a Boyle's Law problem? If so, make sure you are as minimally negative (remembering the tank will be more positive as it empties) which will require a minimal amount of air in your BCD. Then there is lung volume....I know this causes me to have issues. Breathing is the key for me.

 

[billt4sf]

will more gas expand and provide more lift, thus causing buoyancy to be affected more over a smaller ascent

Yes. That's why you want the smallest amount of lead you need to get you down. Then, when you're down, the bubble in your BC will be smaller and thus easier to manage.

- Bill

 

[stuartv]

Add: I said you could be overweighted. But, you could also be fine on weight. It's just something to check.

Once you get your weight sorted, what I would do is get in the pool with a full tank and lay out flat on the bottom, with an empty BCD. Just try to lay there and relax, in good diving position (head up, knees bent so the feet are up and fins are parallel to your torso and thighs). Once you feel like you're totally relaxed and your breathing is under control, then start to add little squirts of air from your BCD. One squirt at a time and then a full inhale and exhale before the next one. Find the point where you just start to rise up when you inhale all the way. Pause to relax again. Don't rush it! Then add one more little squirt and inhale to start yourself rising up off the bottom. Stay relaxed. No hand or feet movement. Just let your inhaled breath do the work of lifting you up. Once you get off the bottom, use your breathing to control it. The key there is to start where you've very slowly worked yourself up to the point of being just positive enough to ascend without doing anything but inhaling all the way - and staying relaxed and breathing slowly and easily the whole time.

As you go through this, you'll probably actually find that when you start to ascend toward the surface, you'll start to go either head up or head down, instead of staying in good horizontal trim. That is an opportunity for you to move weight around to get your trim sorted out.

Disclaimer: I am not an instructor or any kind of dive professional. This is just my own thoughts on how I would approach getting my initial buoyancy under control. I think they keys are taking your time - time to get relaxed - and very (VERY) slowly adding air to your BCD to find the point where you can cycle around the neutral point by inhaling or exhaling.

 

[stuartv]

will more gas expand and provide more lift, thus causing buoyancy to be affected more over a smaller ascent (say, 5 feet, which is common in people having buoyancy issues). Is this simply a Boyle's Law problem? If so, make sure you are as minimally negative (remembering the tank will be more positive as it empties) which will require a minimal amount of air in your BCD. Then there is lung volume....I know this causes me to have issues. Breathing is the key for me.

Yes.

If you use an AL80 and are properly weighted (with a full tank), you will start a dive 6# negative. That is because an AL80 holds ~6# of gas, so when it's empty it will be 6# more positive than when it was full, which means you will be neutral when it's empty if you were 6# negative when it was full.

Imagine that you start the dive with 6# more lead than you need. That means you are actually 12# negative at the start (and still 6# negative at the end).

With proper weighting: At the start, you get to your target depth (say, 10m) and you have to add enough air to balance out being 6# negative. That is 2.7 liters of air. If you are at 10m, with 2.7l of air in your BCD, you will be neutral. If you inhale and start to rise, let's say you rise up by 2m. The ambient pressure has dropped from 2ata to 1.8ata. That is a 10% drop in ambient pressure which means your 2.7l of air will increase by 10%, courtesy Dr Boyle. So, instead of 6 # of lift, it is giving you 6.6#.

With 6# of weight more than you need: Everything the same except, when you get to 10m depth, you have to compensate for being 12# negative, so you have to put twice as much air in your BCD - 5.4l. Now, when you rise up 2m, the air in your BCD will still expand by 10%, so it has 10% more lift. But it's 10% of 12 pounds, instead of 6#. So, when you rise up 2m, you will now have 13.2 # of lift in your BCD.

Instead of an extra 0.6 # to compensate for, you'll be trying to compensate for an extra 1.2#.

This is just a simple example to illustrate how extra lead makes buoyancy control harder.

 

[Themerrydiver]

I have been struggling with finding neutral buoyancy. On my OW training dives I had issues with popping up like a cork and bouncing off the bottom (luckily in a sandy area.

So I went to my friend's pool over the weekend and tried to do some work on this only to have even more issues. I know that in a pool that is only 9' deep max it can be hard to stay neutral but I was either bouncing off the bottom or basically sitting at the surface with my tank almost out of the water.

I go down to depth and add a little air in my BCD. I felt neutral but as I would exhale I would hit the bottom and then upon inhaling I would pop up.

I did notice I had some air trapped in my BCD and using the manual deflate button didn't help so I had to use the shoulder dump as I angled my left shoulder down. This helped but I would still pop up.

I am at a loss as to what I am doing wrong here. Could be my weighting or could be I am just terrible at diving. Which I hope isn't the case but at this point I am seriously questioning my ability to dive and dive well. (side note: I am my biggest critic and know it is a big fault of mine as I can be very hard on myself)

I have a three tank dive trip this Sunday to the West side of Catalina and was hoping I could get some tips, pointers or suggestions from the more experienced divers and instructors out there.

I wear a 7 mil wet suit, 5 mil gloves (which I hate and have little to no dexterity in but that is another thread), Deep 6 fins, weigh 189 lbs and currently have 26 pounds of weight. 18 lbs in my BCD integrated weight pockets with 4 pounds each in my trim pockets.

If I forgot any details you may need to give me tips please let me know.

Thank you all for helping me through this journey. From prior to my OW class to know I have had some great advice and look forward to more.

I'm a novice so buoyancy has been a bit of an issue. I found that my breathing - how big of a breath and how slowly I let it out made a big difference. I was breathing too heavily and exhaling too hard. Slowing my breathing on intake and exhale seemed to really help. I got good advice my diving Honey and it worked but I'm no perfect example for sure!

 

[TMHeimer]

I'm a novice so buoyancy has been a bit of an issue. I found that my breathing - how big of a breath and how slowly I let it out made a big difference. I was breathing too heavily and exhaling too hard. Slowing my breathing on intake and exhale seemed to really help. I got good advice my diving Honey and it worked but I'm no perfect example for sure!

Yes. In other words breathe normally. Other than purposely breathing with fuller or emptier lungs to ascend or descend over something, I've never really given any thought to my breathing.

 

[J_Rod]

Yes.

If you use an AL80 and are properly weighted (with a full tank), you will start a dive 6# negative. That is because an AL80 holds ~6# of gas, so when it's empty it will be 6# more positive than when it was full, which means you will be neutral when it's empty if you were 6# negative when it was full.

Imagine that you start the dive with 6# more lead than you need. That means you are actually 12# negative at the start (and still 6# negative at the end).

With proper weighting: At the start, you get to your target depth (say, 10m) and you have to add enough air to balance out being 6# negative. That is 2.7 liters of air. If you are at 10m, with 2.7l of air in your BCD, you will be neutral. If you inhale and start to rise, let's say you rise up by 2m. The ambient pressure has dropped from 2ata to 1.8ata. That is a 10% drop in ambient pressure which means your 2.7l of air will increase by 10%, courtesy Dr Boyle. So, instead of 6 # of lift, it is giving you 6.6#.

With 6# of weight more than you need: Everything the same except, when you get to 10m depth, you have to compensate for being 12# negative, so you have to put twice as much air in your BCD - 5.4l. Now, when you rise up 2m, the air in your BCD will still expand by 10%, so it has 10% more lift. But it's 10% of 12 pounds, instead of 6#. So, when you rise up 2m, you will now have 13.2 # of lift in your BCD.

Instead of an extra 0.6 # to compensate for, you'll be trying to compensate for an extra 1.2#.

This is just a simple example to illustrate how extra lead makes buoyancy control harder.

Thank you for that! I worked simple Boyle's Law problems before I asked the question, but couldn't get into to it as deeply as you did, without your explanation of the other data. It certainly make sense. Hopefully it helps punk, too. It was his OP.

 

[Dizzi Lizzi]

Pool work really helps me. Its tougher because its so shallow but it makes me see how long it actually takes me to settle down. Much much longer that I think. But its a no stress situation as there are not pretty things to distract me and cause me to dart around.

Add: I said you could be overweighted. But, you could also be fine on weight. It's just something to check.

Once you get your weight sorted, what I would do is get in the pool with a full tank and lay out flat on the bottom, with an empty BCD. Just try to lay there and relax, in good diving position (head up, knees bent so the feet are up and fins are parallel to your torso and thighs). Once you feel like you're totally relaxed and your breathing is under control, then start to add little squirts of air from your BCD. One squirt at a time and then a full inhale and exhale before the next one. Find the point where you just start to rise up when you inhale all the way. Pause to relax again. Don't rush it! Then add one more little squirt and inhale to start yourself rising up off the bottom. Stay relaxed. No hand or feet movement. Just let your inhaled breath do the work of lifting you up. Once you get off the bottom, use your breathing to control it. The key there is to start where you've very slowly worked yourself up to the point of being just positive enough to ascend without doing anything but inhaling all the way - and staying relaxed and breathing slowly and easily the whole time.

As you go through this, you'll probably actually find that when you start to ascend from the surface, you'll start to go either head up or head down, instead of staying in good horizontal trim. That is an opportunity for you to move weight around to get your trim sorted out.

Disclaimer: I am not an instructor or any kind of dive professional. This is just my own thoughts on how I would approach getting my initial buoyancy under control. I think they keys are taking your time - time to get relaxed - and very (VERY) slowly adding air to your BCD to find the point where you can be cycle around the neutral point by inhaling or exhaling.

I would add when people say inhale all the way, they don't mean to capacity, but rather a normal inhale. Because when diving you are not taking huge in and out breaths. Good luck, you will get it. So will I, eventually